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Old 04-20-2017, 05:22 PM   #1
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Vorshlag BMW E46 M3 CSL - V8 Downforce Monster Track Car ("Chainsaw Massacre")

Project Introduction - April 20th, 2017: Welcome to another of Vorshlag's detailed Build Threads, this time chronicling possibly one of the craziest cars we have ever built. Even though its is 4/20 day, this is no drug induced delusion - what started with more of a dare has grown into a wicked track car build for one of our customers. This car is called the Chainsaw Massacre - and yes, I will try to explain the name (given by the car's owner) in the paragraphs below.

This E46 chassis getting a custom roll cage in late 2016

The goals on this build are similar to the factory 2003 BMW M3 CSL, just taken to the extreme: start with a BMW, shoot for lower weight, maximum power, maximum tire, maximum downforce, maximum brakes, maximum reliability. To that we are adding full safety gear (cage, halo seats, belts, fuel cell, fire system) and using a plentiful chassis that is easily replaced if damaged in a track event. This "big tire/big engine/big aero" combination is a simple formula which we have built around before, but this time we have a customer that understands the benefits, and very few class rules or budget restraints to hold us back!

This shows where this project is in April 2017, after 5 months of work (with a few long delays waiting on parts)

Target weight is 2600 pounds soaking wet, with the ability to add ballast for series that require higher minimum weights. Target horsepower is 750 flywheel (650 whp), using a large displacement naturally aspirated aluminum LSx V8 engine. Tires chosen are "the biggest DOT Hoosiers available": 335F/345R with the ability to use a 200 treadwear tire of similar size when required. We are also using the biggest wing that AJ Hartman builds (72x14"), along with a diffuser (for when the wing isn't allowed) and a mega sized front splitter, canards, and hood venting up front. There are a few minor "street car" concessions like roll up windows, working wipers and lights, to meet the bare minimum "street car" racing series rules. There are virtually no racing class power-to-weight rules that apply to this build, but we're shooting for around a 3.5:1 to 4:1 pounds per horsepower - which is closer to a FAST sport bike than any production sports car. This E46 is built to run with McLarens on track.

Is this just empty smack talk? Before the 'Debbie Doubters' chime in, yes, these are all attainable goals using proven components and build practices we have used in the past. Our caged, metal bodied BMW E36 coupe with an LS1/T56 drivetrain and big CCW Classics shown above (the "E36 LS1 Alpha") was 2508 pounds soaking wet.

The power numbers used are from a proven 7.7L LS engine combination from HorsePower Research (HPR), an engine shop that I am a part of. We already have the 468" aluminum LS shortblock built, just waiting on the heads. No, we won't be using some "destroked" high revving nonsense, but a big bored, big stroke, standard deck block with sleeves. #MURCA We have proven the effectiveness of this tire package, the aero tricks, and more on our red Mustang as well as other track cars. This BMW will be one BRUTALLY fast car that should go, stop and turn like very few other unibody street legal cars.

We always take pictures to update our customers during their builds anyway, so why not chronicle the builds in detail for the public? Spread the insanity far enough and we hopefully find more like-minded customers. As with most of our build threads from the past 15 years, this one will be cross-posted to a number of forums (which we either sponsor or they like us enough to let us post there), including:
All of the pictures can be clicked for higher rez versions (#watermarked #triggered), so you can see the details. These build threads take a lot of time to put together but people seem to enjoy them, so I'm going to keep writing them up like this. If you don't like the way this is written, I'm not putting a gun to your head and making you read it.


The path to this balls-out E46 V8 build wasn't a straight line - it took 2 previous cars and several years of work with this customer to get him to trust us enough to build something this crazy for him. Things like the 18x13" front wheels are borderline absurd. And while some of the pictures shown are just shown to make fun of silly fads, like #DollarBillzonDemLips, this is a serious build that will be a bit insane to drive.

Not everyone would want a car like this, or could even drive a car this light and powerful without a bunch of electronic nannies. This idea started after Mr. Chainsaw was frustrated with his supercharged track Mustang, which had heat issues on track - just as ALL boosted track cars seem to have. Overheating, heat soaking, unusable power delivery, high weight, low reliability, and high consumable costs.

After two years of improvements to the cooling system, packaging things to better vent the hood, and adding ever larger heat exchangers the Mustang was getting a lot better, but the weight was still fairly high and it was making for a frustrating experience on track for the owner. Just like we told him from the beginning, and what we tell everyone who wants to use a blower/turbo on track: power adders are great for making lots of horsepower for very short amounts of time, but they typically make compromised track cars. A power adder also doesn't make an engine MORE reliable... it does the opposite.

This highly modified Mustang (which he called the Chainsaw) was run at many HPDE events as well as Optima Ultimate Street Car qualifier, where it was damned fast. The owner enjoyed the variety of contests they do during Optima events - speed stop, autocross, and time trial. So that series became a focus for a "dedicated race car" to be built in the future. Which is now.

Mr Chainsaw thought about a McLaren, but wanted something that could be built faster for less, and more unique. Once we had a detailed build plan and estimate for this V8 M3, we then cautioned him that driving this car would be fairly difficult. Jason convinced him to let us build him a "trainer car" to help sharpen his skills on track. The supercharged Mustang making 640 whp and was a just a damn missile on track, using the power to pass anything on the straights.

A stock powered 1.8L NB Miata would teach him how to maximize corner speeds, braking, and patience! He set his ego aside and gave us the go in the Summer of 2015. Jason and I found this 2003 Miata and our team turned it into a trainer with full safety (cage, seat, harnesses, fire, remote kill switches), excellent suspension (MCS, Hyperco, Vorshlag + bushings, bars), upgraded brakes (NB Sport brakes, Vorshlag lines, custom cooling, G-LOC pads, Motul fluid) and track worthy wheels/tires (17x8" Enkei & 225mm Rival-S), and lots of cooling (Mishimoto rad, custom oil cooler, new water pump & hoses, etc).

The goal of the track trainer was a super reliable car that he (and others in his family) could use to "beat on like a rented mule" at track events, to improve and refine driving skills. He hired a driving coach/data analyst as well. We built this car in 17 days and it was actually quite a fun little project to be able to do a Miata "right".

Jon here at Vorshlag did the graphics (stripes, number boards, etc) on the Miata. Notice the chainsaw wielding mouse wearing a "Texas Chainsaw Massacre" movie-style hockey mask? You guessed it - this car is called Chainsaw Mouse, and the "Texas Chainsaw Massacre" theme carried over into the V8 M3 CSL we are now building. The owner has been running this Miata for two seasons while the build plan for the E46 solidified, we found a good chassis, and carved out time in our shop schedule to dedicate to the build. Our head fabricator Ryan is doing 95% of the work on this project while also juggling the the '69 Camaro track car build, plus does all of our cage fab work.


Some might not agree with using an E46 M3 Coupe chassis for a wild track build, but let me explain. While we could have started with a C5/C6/C7 Corvette chassis and made something equally as fast, and it might have even been "easier", that wasn't the right car to start with on this project. Why? The customer's wife already had a supercharged C7 Z06, and while its fun and fast, the "Corvette solution" isn't everyone's solution.

While modern Corvettes have plenty of benefits, the also come with a few downsides: a SMALL cockpit, very low seating position, somewhat poor visibility, and extreme difficulties in adding a proper roll cage to the chassis (they don't even have a real floor). We can also make a steel unibody BMW lighter than a full frame/composite bodied C4-C7 Corvette for the same amount of weight removal work ("body on frame" technology is one of the least efficient ways to build a light/rigid chassis). Besides, you can't swing a dead cat at a track event and not hit 30 Corvettes. The roll cage issues are real. Corvettes are easily the most difficult car we build cages for due to the cockpit and greenhouse shape and difficult to access mounting points.

To build a safe roll cage away from the driver on a C4/5/6/7 Corvette you often have to move bars OUTSIDE of the body

After several discussions we narrowed in on a BMW E46 Coupe to start with, for a number of reasons. We think the modern BMW 1 and 3 series chassis are unique in their ability to become excellent track cars with V8 swaps, and they can take a LOT of power. We've proven that with the E36, E46 and E90 chassis many times.

Left: The BMW E90 swallows a Coyote 5.0L V8. Right: BMW E36/7 Z3 with LS1. Both built or heavily reworked at Vorshlag

Here's the list of positives with the E46 chassis.

1. Strong, lightweight unibody chassis with "good bones" to build upon. The roof panel is easily replaced with carbon (and the CSL came with carbon from the factory), as are almost all other body panels - and there are good options from the aftermarket. BMW made 4 million E46 chassis globally, which makes them both abundant and cheap.

2. The interior room, ergonomics, seating position and visibility are superior to most low slung "sports cars". These give you an upright seating position that is favored by many drivers. You don't "lay down in a coffin" like in a Corvette since the BMW passenger compartment is fairly large and spacious. This lets us build a roll cage much further away from the driver, which increases safety and comfort and gives us better entrance/egress.

3. These cars have a fairly efficient aerodynamic shape for such an upright greenhouse. It has a sleek coupé styled body with a short trunk, long hood, and generous cabin. The look of the E46 coupe is more modern and timeless than the E36 which is more angular and becoming a bit dated.

4. The E46 engine bay is 2" wider than the E36 and easily swallows an LS V8, and the stock transmission tunnel accommodates a large T56 transmission.

5. The suspension is pretty good (McStrut front, independent rear suspension), it has decent wheel/tire room (especially the M3), and the brakes are not half bad (with excellent upgrade options). Of course we won't leave any of these items stock.

We started hunting for a 2003 BMW E46 M3 coupe chassis (the same year they made the M3 CSL) and found this one locally for a good price in late 2015. Once the project got underway (Winter 2016) we began by cleaning it up and getting the frame checked before real work began. The early build details follow below.


This chassis was already partially stripped and had "seem some fun" in it's past, so it needed a good inspection, some squaring up, then a few preventative reinforcement fabrication tasks before major upgrades got underway. First we took the M3 to our friend's bodyshop to put on his chassis table, check the diagonals, and square it up before we began the roll cage installation. Then we reinforced a number of common weak sports on the unibody. After that we began to strip the interior in preparation for the roll cage, even removed the roof to replace it with a replica CSL carbon version.

continued below

Last edited by Fair; 04-21-2017 at 09:05 AM.
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Old 04-20-2017, 05:29 PM   #2
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continued from above


The two main series that this car will be competing in don't require a roll cage, but its a damned good idea when you are planning something this fast. Before you want to ever put an elaborate, welded roll cage structure into any car you want to make sure the chassis is square and true. Nothing worse than caging a bent chassis - you just wasted a lot of time and ruined the tub.

We knew this car had a light front hit at some point, as it was missing most of the front sheet metal that bolted on: bumper, bumper cover, lights, radiator support, plus and the hood & front fenders were a bit munched. Otherwise it looked like a solid, rust free M3 chassis with the M3 specific front spindles, rear subframe and rear fenders.

In late summer 2016 I delivered this Coupe chassis to our friends at Heritage Collision Center in Sherman, Texas for an inspection and squaring up. I also brought them a new factory front radiator support to install and align into the "front doghouse" of this car.

They put it on their frame table and measured diagonals on known chassis points against BMW factory data. After a few tugs it was square and ready for the front radiator support, which they installed and trued up as well. I picked it up and brought it back to Vorshlag so we could begin.


Once the chassis was trued up we had a bit of a wait while the schedule cleared up and the owner was ready to really begin this project. We did sneak in the rear subframe reinforcement work early on before we "officially" began. This is where we beef up the rear subframe mounts at the chassis, which is a factory approved fix for an issue they acknowledged on the E46 chassis. We did this work when we had a tech "under tasked" for a couple of days, back in the Summer of 2016.

The BMW E46 chassis' primary weakness is in the trunk floor right where the rear subframe mounts. There is a lot of flex in the rubber subframe bushings which allows for constant movement. Over time this slide-hammer like movement can cause fatigue cracks in the sheet metal mounts. If the cracks are ignored long enough it can cause failure of the mounting areas.

Donnie put the M3 on a 2-post lift and removed the rear subframe assembly, which holds the differential housing and the rear suspension. Normally when doing this E46 reinforcement job we would remove the sloppy rubber factory mounting bushings for the subframe and diff and replace them with aluminum or polyurethane. We actually procured a second complete E46 M3 subframe for this car, since we had major modifications in mind for those bits. So the stock rubber bushings were untouched at this point.

With the subframe assembly removed we can finally inspect the trunk floor mounting points. Then the paint, seam sealer, and undercoating materials are removed from these areas where the plates will be welded - our air powered OBX "Crud Buster" tool makes quick work of these coatings. The reinforcement plates are CNC laser cut and bent pieces we source from CSM. These have a much larger footprint than some other reinforcement plates we have used. The CSM plates cover more area, which better covers some of the larger cracks we have seen in these cars.

This time the cracks were visible before removing the paint - they had propagated a good ways. Luckily we only found cracks in one of the four mounting positions, which is pretty good for an E46 of this age. Often we see cracks are all 4 points of contact. In the dozens of E46 cars we have done this work to only once did we find a car without any cracking. Like I said, its the primary weakness of this car, but easily fixed and reinforced.

Before the reinforcement plates are welded on we have to "drill stop" the cracks and TIG weld them for a proper repair. The small drilled holes at the end of the cracks removes stress from the sheet metal and keeps the cracks from propagating while they are being welded up.

Once all of the cracks were repaired, then all four plates were TIG welded to the chassis, it was time for seam sealer, primer and some paint. Once the paint dried the stock rear subframe assembly was bolted back in place, to allow the car to roll around. In the end it took about 11 hours + $250 in materials to get these areas properly repair and reinforced, but they should be good for life now. We had big upgrade plans for the second M3 subframe we purchased for this car, which I will show in a later post.


The second common weak point on the E46 chassis, as with many McPherson strut cars, is in the actual strut towers. The sheet metal is a bit on the thin side and virtually all of the vertical suspension loads pass through the strut and into the chassis via these two towers. With a big enough impact you can deform or crack the sheet metal here. It's even worse with sticky race tire loads. Sometimes the towers develop cracks simply from fatigue - again, soft bushings allow for a lot of extra squishy movement, which flexes the metal over time.

Below is a common upgrade we do on many BMW chassis, where we reinforce the tops of the strut towers. The damage shown on the silver E46 M3 track car below is a perfect example of why this work is needed.

This customer saw the tower reinforcements done on the Chainsaw Massacre E46 M3 CSL-clone and wanted the same thing done to his dedicated M3 track car. Good thing, too - when we pulled the strut tower brace off we found a series of massive cracks hidden from view, which you can see above.

The cracks were each "drill-stopped", TIG welded, sanded smooth, then a pair of the BMW E46 reinforcement plates were welded into the towers from underneath - effectively doubling the thickness here. The areas were primed and the car went back on track.

Before the color matched paint arrived to re-shoot the tops of the towers this car was in a track incident. This snapped the right front Bilstein Club Sport inverted strut like a twig, ripped the tie rod out, and broke the control arm and wheel - but the strut tower was fine. I can say with confidence that this reinforcement work saved this strut tower from total annihilation. Doubling the thickness of metal here is key.

Back to the E46 M3 CSL build - Ryan started by pulling the stock front suspension off and out of the way. Then we ordered these stamped steel E46 strut tower reinforcement plates from BMW (Part # 51717036781 ), which are rounded and match the shape of the E46 strut tower from underneath. These are often just slipped in and bolted between the strut tower and the top mount, but we would weld them on for more strength and longevity.

The paint was stripped off the top of the strut towers with our OBX stripper tool. Then the reinforcement plate was bolted in using a fixture and TIG welded around the round opening at the top and along the slotted strut tower holes. There was some prior damage to the lip of the strut tower opening that we repaired and now looks new.

The paint was also stripped from the underside of the tower and from the reinforcement plate. Ryan MIG welded the plate to the tower from underneath with 6 stitch welds as shown. These areas were then covered with seam sealer and primer paint.


In preparation for the roll cage and seat mounting we needed to get the chassis completely stripped and ready for welding. Since this was a "complete build" we tackled the additional work of removing all of the body wiring, tar insulation, and even some unnecessary unibody structure. When you are looking for hundreds of pounds of weight loss you have to chase every pound!

We had Mr Chainsaw test sit various racing seats in our lobby. He liked the Sparco Circuit II seat, which have an integral halo section to prevent side impact neck injuries and high leg bolstering. I also like this seat and have it in one of our shop cars. After we test fit one in this car, I ordered two new seats from Sparco for this build.

The work of removing the dash, wiring, and plumbing from the car to get it down to a bare rolling chassis takes time. It isn't super exciting work but it is all necessary when you are looking to minimize weight as much as we are here. "Just leave the stock wiring harness" might be appropriate for some builds, but not one this extreme.

continued below
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Old 04-20-2017, 05:34 PM   #3
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continued from above

Between the engine goals and potential cornering loads (Hoosiers + full aero), a dry sump oiling system was decided early on.

Ryan test fit an oil settling tank we had from another project under the M3's dash, but it just wasn't the right place for this chassis (it will go in the back seat area instead). Then the tedious job of removing the steering column, HVAC box, and dash assembly was tackled. Its all gotta come out for cage work...

This outer dash skin came out cleanly and will be reinstalled after the cage is built. The steel OEM dash bar structure was removed and will be replaced with a horizontal tube, connected under the "skin" of the dash, to joint the front of the roll cage. We will have to replicate a lot of these little hidden brackets to hold the top skin of the dash in place afterwards, but that's how you save more pounds - little bits at a time.

The front windshield and back glass came out next. Since we planned to re-use the front windshield (it was un-pitted and perfect) we hired a professional windshield installer to remove these two pieces of glass. This allows more access to build the roll cage as well as roof panel removal (more on that below).

After the dash structure and skin came out, this giant rats nest of wires (above left) was left behind. Yes the main body wiring harness was completely removed. We would have to pare this down so far that it makes more sense to replace it with a more streamlined, custom built chassis wiring harness. This harnesses was later weighed and it came to 49.4 pounds of wire, just from behind the firewall. This includes the giant cluster of wires under the dash, under the carpet, and in the trunk area.

The engine bay was already partially stripped, as this car had no drivetrain or engine wiring harness when we bought it. But the rest of the underhood clutter had to come out, as nothing OEM was being re-used up there.

The brake and clutch master cylinders, brake booster, ABS module, brake hard lines, and all sorts of plastic panels were removed and scrapped. At this point the engine bay was mostly stripped but even more brackets and panels would be removed later.

Many of the old parts were stored on a wire shelving unit. This way anything we need to re-use is kept together with the rest of the customer's parts. These can be rolled away and stored when not needed.

At this point the interior looks pretty barren. But we're not stopping here. No, NO! WE NEED MOAR!!!


We were looking for every pound, remember? Next up was the heavy asphalt/tar sound insulation panels stuck all over the interior and trunk areas. These materials are a chore to remove, but it adds up.

A heat gun + a variety of scrapers + lots of elbow grease are the best way to remove this stuff from a BMW. Trust me, we've tried all of the methods - freezing with dry ice, power tools with wire wheels, and sandblasting - and the heat gun is the cleanest, fastest way for the BMW insulation.

17.7 pounds of tar paper came out of the interior and trunk. But it left behind this tacky adhesive goo....

The car still rolls at this point so it was shoved outside and the electric pressure washer was used to blast every surface of the chassis, inside and out. 2500 psi gets all the dirt and grease off the chassis, but it won't make a dent in the adhesive residue.

Over the years we have tried numerous degreasers and petroleum products and found that soaking the adhesive with mineral spirits works like a charm. It softens the adhesive enough to wipe it away, but doesn't damage the paint. Of course we're going to paint this entire chassis inside and out later, but having bare metal during the build process might allow it to flash rust. So .... heat gun + mineral spirits works best on this stuff.

continued below
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Old 04-20-2017, 05:34 PM   #4
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continued from above


We still weren't ready to start the roll cage, and needed to do something about the power moon roof that was in the way.

Left: 72.0 pound factory sunroof cassette. Right: AJ Hartman carbon sunroof delete panel at 1.4 pounds

Like most E46 BMWs, this one had a factory retractable sunroof option. The non-M E46 almost always has a sunroof, but a few E46 M3s came without a sunroof - including the CSL.

The 72 pound power sunroof assembly (they call it a cassette) is not only a heavy thing but it gobbles up head room in these cars. We had talked early on about a carbon fiber sunroof delete panel, which we have done on a number of E46 chassis to knock weight out of the roof while gaining 2.5+ inches of headroom (like my E46 330Ci above). Another AJ Hartman pieces that is an easy "bolt-in" replacement you can swap in over a couple of hours.

Since this is a 2003 BMW M3 CSL clone of course we have to use the CSL's full carbon fiber roof panel, duh! We had AJ Hartman make an exact replica of this CSL roof panel, which Mr Chainsaw agreed was more appropriate for this build. Ryan started the roof swap by removing the two roof seam covers, then drilled out spot welds with a small spot weld cutter.

Ryan received some help from our CNC operator, also named Ryan aka: "R3". The two Ryans then finished removing the 100+ spot welds around the perimeter of the factory steel roof panel, prying the glue loose after these spots were carefully cut through. The front and rear glass removal was crucial in this step; the roof came off in a little under 6.5 hours.

The OEM roof weighed 96.1 pounds (24.1 for panel + 72.0 for sunroof cassette). The new AJ Hartman carbon fiber roof came in at 6.9 pounds, for a total savings of 89.2 pounds - way up high in the roof! Not only did we lose the equivalent mass of a "young adult" the interior gained about 2.5" of headroom. We also had ample access for building the roll cage.

The CSL carbon roof panel went on easily and bolts in place using 4 factory threaded bolt holes, which fit the roof section perfectly. Ryan had to do zero adjustment, custom fitting, or hole enlargement - it just fit.

Once the cage work is finalized and before paint this will be bonded to the body structure just like the factory E46 M3 CSL roof is, plus there are the four back-up bolts as well.


The back seat was never going to be used in this build, so to lose some additional weight we looked at the rear seat bulkhead structure and decided to remove it before the cage began. There is a lot of easy weight that can be removed from the back seat, and in our 2001 BMW E46 330Ci we found 63.8 pounds in the back seats + headliner and another 10.4 pounds in rear speakers and a few trunk brackets.

Compared to my 330, this M3 needed an even sharper scalpel this time. We weren't looking to "skin" this car and put it down over a tube chassis or anything, but redundant structures that could be removed would be. There was some easy weight loss in the rear seat bulkhead perimeter structure and rear window "speaker deck" panel - which would have their chassis stiffness more than replaced with roll cage structure. We will make lightweight interior panels to separate the trunk from the passenger cabin.

There were probably another hundred spot welds that were cut for all of these brackets, panels and sheet metal structures in the back seat area. These were cut into small pieces with a reciprocating saw and pried loose without warping or damaging the surrounding structures.

Of course I forgot to weigh all of this before the scrap metal guys came and picked it all up, but it was around 15-20+ pounds of sheet metal in addition to the back seats, interior panels, and trunk brackets that were also removed (with weights noted on our red 330). Now the car was ready for a roll cage!


The intro post in this build thread has already run long, so we better cut it short. Nothing really earth shattering done in this first series of posts, just showing the steps needed to remove weight and add longevity to this E46 chassis. Again, my goal weight guesstimate is 2600 pounds soaking wet with a dry-sumped LS stroker, T56 Magnum, giant wheels and tires, wide body work, full aero, and the required door glass + heater + wipers required for street use.

In my next installment in this build thread I will show the roll cage fabrication work. I will also cover seat installation, custom "low profile" door panel construction, subframe reinforcement, the 8.8" Ford IRS diff swap, and more. We will discuss the classes we are building toward in NASA and Optima, and the rules/performance differences between them.

I tend to show details and pictures of this build and more "in real time" on our Facebook page and in our irregular "this week at Vorshlag" videos on our Youtube channel. Look for those and like/subscribe/whatever it is you are supposed to do there if you want to see the progress on this build sooner.

Until next time,
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Old 04-21-2017, 07:42 PM   #5
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Old 04-25-2017, 10:03 AM   #6
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Old 05-19-2017, 08:26 AM   #7
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Project Update - May 18th, 2017: This round we will cover a number of fabrication tasks, including the roll cage and seat mounting. We also did a good bit of work to both the front and rear BMW M3 subframes, modifying and reinforcing them. The rear subframe was also modified to accept a different differential housing (for 8.8" IRS) and the reasons for doing that are explained in detail.

A pair of custom "low profile" inner door panels were built to allow for operational door window glass, which is one of the stock features retained to compete with this car in the Optima Ultimate Street Car series. We talk about concessions needed for Optima as well as the NASA class we are building for at the end. Let's get started.


Before we started building the roll cage we needed to pick the seat(s) for this car. This is a critical decision in any race car build, as it needs to fit the driver(s), be comfortable and supportive, and provide the proper level of safety for the class/power/driver. Then it needs to be mounted correctly, safely, and with the right tilt/height/fore-aft placement.

Like with all seat installs we do, we started in our lobby with the customer - test sitting in about a dozen different seat models. We had a number of race cars in the shop with most of these seats also, so he got to sit in them on stands and in cars. We're looking for head placement relative to the halo, shoulder height relative to the harness slots, and width sizing in the shoulder and hips. In the end the car's owner and I both fit the best in the Sparco Circuit II seat (above right). Wait... why does it matter if I fit? Well, I might drive this CSL clone in a few events at his behest. The sacrifices I have to make... :p

Some marketing speak from Sparco: The Circuit LF is an lightweight competition seat specifically designed for road course (ie: circuit) use. Made from aramadic fiber-reinforced fiberglass, the Circuit has an ultra-light shell (LF is for lightweight fiberglass). The integrated head bolsters offer added neck protection and the driver’s legs are also supported well with high side bolsters. The shell is wrapped in an impact-absorbing and fire retardant fabric that helps hold the body in place, with everything meeting FIA approval.

The Circuit "II" version is a more appropriate width for "adult humans" - almost nobody over 100 pounds can fit in the "regular" sized Sparco or Cobra seats (which is why we rarely have them in stock). And the weights published for all seats are always low - I don't think they include the weight of fabric and cushions. Of course we weigh everything, and this halo style racing seat is 24.10 pounds.

Initially we had hoped to use an E46 seat bracket design that was identical to one we fabricated for another E46 race car we are building, shown above right. This beefy bracket is made from tubular and angled steel, is very rigid, and has integral anti-sub-mounts. This "chassis bracket" is made for use with a slider on the driver's side, and is more substantial than the seat brackets used in my TTD classed E46 330, but sit a hair higher. I like this design and might go back and have the 330 brackets replaced with some like this.

At this point the factory lateral seat braces were still tack welded in the floor, and the driver's Sparco racing seat was mounted. We grabbed a similarly sized passenger seat (MOMO) and fixed bracket from another E46 race car and began the roll cage construction around them. The car owner came by for a test fitting, and it was apparent that the seats were going to be too high relative to the roll cage for safe use without a helmet (ie: for the Optima "road rally" event), so we had to go back and re-examine the seat mounting.

We had little choice but to cut out these factory floor seat risers. This was a tedious task - cutting dozens of spot welds - but it gained the room we needed to make a cage that was safe enough for limited street use without a helmet. Lowering the seat like this normally isn't needed for racing use on an E46, but was deemed necessary for the HUGE compromise of running with "a cage on the street" - which is never an ideal situation.

Once those risers were removed there was even room gained by removing one layer of sheet metal from the transmission tunnel - which had two layers with an air gap between then. This extra layer was angled and took up 2" inboard. Removing it centered the seat to the steering column better at the new lower height.

Ryan built a new driver's side bracket that fit the new contours of the remaining E46 floor pan, which were still anything but flat. The two sizes of tubing used were to make the inboard side fit better next to the tunnel.

The "feet" are flat steel and there are uprights that are used to clear a big hump in the floor, but the overall structure is still more than 2" lower than before. There will be additional structure added under the car to reinforce the seat mounting points, which will tie into the cage.

Now that picture above shows Ryan in the driver's seat and he's around 6'4" tall - yet his head has massive clearance to the roof and upper cage bars. We kind of went to extreme lengths on this install to gain a massive amount of headroom, and shorter driver's might get a thicker seat pad, but for street use without a helmet its finally deemed safe. Of course we will add SFI padding to all bars around both occupants.

This is the final seat mounting with both Circuit II seats. The driver's side is on a slider but the passenger side is fixed. Both seats are 2+ inches lower than the initial fitment - you can scroll up and see the first mounts that kept the 3" tall seat braces and see how much higher the seats are relative to the roof and upper cage bars.


We talked at length about cages vs roll bars in our last update to our "daily driven track car" project build thread, which is the E46 330 we built and I race in NASA TTD Time Trial class. That car's purpose was to show how far we could go on track in a "street car", and for that build a roll cage wasn't appropriate. It has 245mm Hoosiers and less than 220 whp.

The Optima series does you no favors when it comes to safety allowances, but this V8 powered M3 will have more than TRIPLE the horsepower of our TTD classed 330. It also has giant 345mm Hoosiers for NASA use, big downforce, and a lot more potential for speed and carnage. So on this M3 a cage is not only a good idea, we consider it a requirement.

Obviously some of the cage progress was shown in the seat mounting section above, but that's because the cage and seat mounting go hand-in-hand - another "concurrent" set of tasks that I am splitting apart for clarity. We also showed "considerable interior structure removal" from the back seat bulkhead in the very first project thread update.

Jon, Jason and I all had input with Ryan so that we were all on the same page with respect to class rules and series requirements for the cage material and layout. We chose 1.75" dia x .095" DOM 1018 seamless steel tubing for this cage. The design emphasis was on getting the tubes as far away from the driver as possible - while still keeping roll up door windows for Optima. This would not be a "wheel to wheel" cage (which has more robust door bars and sometimes additional tubes) but a Time Trial car with very limited street use - I go more into the series and classes this car will run at the bottom of this post. We built the cage with those aspects in mind.

After the main hoop was bent up and set in the car the rear downbars were landed in virtually the same spots as the 4-point welded roll bar we added to our shop 330 last month. This M3 cage happened first and I liked the layout so much I asked Ryan to duplicate the back half for my 330 (minus one of the diagonals in the main hoop; the M3 got two).

Many BMW roll cages you see on the interwebs have these rear down bars landing on the shock towers (not doing coilover rear springs, so that's not useful to us here), or into some elaborate jungle gym of triple-triangulated tubes tying into rear subframe mounts (we've already beefed up the subframe mounts) and everything else. With respect to those cage builders, we just don't feel that any of that is necessary on a time trial car. It's just throwing steel at a perceived problem with minimal return. This is a phenomenon we call: Steelitus.

I already know how these "roll cage design" discussions go, and I'm not here to argue with the internet cage experts. I just know what works well for what we have built in various cars and different racing classes. No, we don't have a chassis jig to measure torsional stiffness / frequency (almost nobody on the planet has these types of tools), and we didn't do FEA on the structure, but this cage will be appropriate for the final weight (2600) and type of racing (Time Trial) this car will do.

The main hoop was placed behind the driver and aligned closely to the factory B-pillar, placing the tubes just ahead of the back seat floorpan kick-up for the fuel tank. The lower landing points were reinforced with steel plate as well as sitting on top of plinth blocks, to raise the cage up off the floor. In the pictures below you can see the plinth structures (below left) and how the cage was dropped at the front to weld the top joints (below right). Dropping the cage off the plinths allows the cage to be lowered by that distance, to get full 360° welds around each tube. This seems common place, but I cannot count how many cages we've seen done without full welds around all tubes. This is one of those "cost saving" features that often happens on lower cost roll cages. I talk more in depth about "why roll cages cost money" in this forum post.

continued below
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Old 05-19-2017, 08:30 AM   #8
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continued from above

Removing the roof panel made the main hoop upper joints a little easier to weld, and we could have done this cage build with the roof installed. Since it was getting a carbon roof to emulate the CSL model and reduce weight, it made it that much easier.

The image below left shows the main hoop being welded to the upper cage bars. Even with the factory roof removed we still needed the plinth blocks on the main hoop landing points to gain enough access for final welding on the top of the cage. The upper door / roof structure panels were still in the way. You can see on the below right picture (with the cage raised up on the plinth blocks in place) the curvature of the upper cage sections and how far up into the roof area they go. More head room, better forward visibility, tighter fitting to the outer panels.

Once the main cage structure was fully welded together the front was raised up on the plinth blocks and they were welded into the chassis (below left). The main hoop was welded to the load spreading plates, which themselves had been welded to the floorpan (below right)

The door bars were a simple "X" style design due to the need for functional door windows. Not ideal, but one of the compromises we had to make for Optima series. We also added a "FIA compliance" bar at the front of the door opening to give more column strength to the side of the cage in the event of a rollover. This is commonly done on road racing cars with high rake windshields and in rally cars. The image below left has the plinth blocks removed, below right has them in place and welded.

With the main sections welded together and to the chassis we looked at additional points to tie the cage into the unibody. The low mounted horizontal bar between the main hoop's lower bars rests right against the rear seat vertical floor section, which was joined to the tub with several stitch welds along this tube. The A-pillar cage bars were also tied to the chassis with some load plates that featured dimple die formed stiffening holes. We may do the same thing at the B-pillars later in the build.

Last but not least, the horizontal harness bar was added after the seat placement was finalized. Ryan added a "taco plate" reinforcement to the X bar joint inside the main hoop.

There's still a few gussets and bits we might add, and some short sections of tube to tie the harness bar into the main "X", but the main part the roll cage is complete. Remember: this isn't the only way to make a roll cage for an E46. This is built as a Time Trial / Optima Street Car competitor, so there are multiple compromises made to meet some conflicting needs.


To race in Optima series you can't do door bars like this and keep all the points. Compromises for rules are all part of the game.

After we realized we needed to keep the door glass, we knew that we would have to rework the factory door panels - which were just too thick to allow adequate room to the driver's elbow with door bars. We prefer for a race car to have fixed Lexan or no door windows at all, then we can gut the structure inside the doors and push the cage door bars out to the outer skin. This always gives more room to the driver - which is helpful to absorb energy in a side impact (more common in wheel to wheel racing). Optima dings you heavily for not having working door glass, so the X-bar layout on the doors was a concession to that series.

We discussed options with the owner and the marked up image (above right) of modified OEM door panels was deemed the right way to go. This allowed us to keep the upper curved plastic section of the factory door panel, which has the inside door handle, a speaker hole, and the upper wiper seals and felts for the door glass. Ryan carefully removed the lower section of the panel, which was plastic riveted to the upper section.

In the images above you can see the detail on the plastic rivets which fastened the two plastic panels together. Once those were cut out he made a cardboard template for the lower section, test fit that to the cage, then transferred the templates to aluminum sheet. These will make for "almost flat" panels, which will gain several inches of width for the cage door bars (removing the "pull" handle and outer arm rest).

With the two aluminum panels cut they were then split along a curved front edge, which would need to be fitted to a curved section of the upper plastic section of the OEM door panel. This gap was filled with more aluminum sheet, then he secured it to the door panel with Clecos and tack welded the pieces together (see below left).

The split sections were fully TIG welded off the car, then the seams were sanded, filled with metal as needed, and shaped for a nice appearance (see above right). The Optima series has car show portions that we cannot ignore, so this work was for those all important "Design & Engineering Points".

The end result adds some necessary protection between the driver's arm and the sharp inner workings of the window glass. It looks good so it should help in the Optima D&E judging, too. We might go back and upholster these aluminum panels, or coat/anodize them in some way. For now we had the clearance needed to get the door bars as far away from the driver's arm while keeping the door windows operational.


Due to the high torque loads from the 7.7L engine we are building for this car we decided it was worthwhile to reinforce the front subframe while the car was being built. When we are building a car to this level there are very few areas that are "just left stock". The factory front subframe was dropped out of the car and bead blasted down to bare steel.

Once we received the subframe back we inspected it closely for cracks, bent flanges, and any other potential damage. This came out of a Texas car so there were no traces of rust or corrosion, and luckily the motor mount sections weren't cracked. This meant we had a good core to start with.

The factory M3 subframe is a welded steel assembly from a number of stampings, but the factory misses a few spots when they put them together, so those were fully welded by our crew.

They also TIG welded in some reinforcement plates to the underside of the motor mount plate, then a second plate was welded in from underneath to "box" in the bottom of this section. We use one of these mounting holes for our LS swap mounts, so we wanted that as strong as possible. Even the subframe mounting holes were seam welded at both ends, to fill in "skipped" sections from the factory.

We were re-using an OEM power steering rack, converted to manual (electric assist) steering, so we also added some tack welds to the back of the steering rack mounts. Once the welding was completed on this and the rear subframe (read more below) it was sent out for powder coating.

There a gloss black powder coating was applied to give this raw steel some corrosion protection. Its a bit flashier than the factory coating, but when you have it down to the raw steel like this, powder coating is the way to go.

The front M3 spindles were also dismantled, glass bead blasted, then "double nickel plated" (a process we tried on a few suspension parts in the past, and it looks great and lasts). The spindles were treated to brand new front hubs, then some of our 90mm wheel studs. We sent the OEM front lower control arms to our friends at SPL Parts for them to model for a billet adjustable lower control arm set with spherical bearings. We should see those soon, but for now the car has the old arms back on to be able to roll around the shop.


Left: Our E36 LS1 swap "Alpha" build saw tons of abuse on the 188mm BMW diff. Right: Our Beta customer broke the medium case

The argument for using a BMW diff in our swaps goes back to 2002 when we first starting our E36 LS1 "Alpha" project. And in 2011 when we kicked off the E46 LS1 development we had the discussion again, but this time with many years of first hand experience with a "medium case" E36 M3 limited slip behind a 500 whp engine and 315mm Hoosiers. We couldn't manage to break the 188mm Medium case but we did have one customer (540 whp) that did - but in his own words, he breaks everything.

This LS powered Miata used an aluminum Ford 8.8" IRS differential mounted in a custom rear subframe

In various V8 builds since then we've used a variety of solutions: the Medium case BMW diff, a Ford 8.8" diff (Miata V8, Beta E36 LS1), and even the 210mm "large case" BMW E46 M3 differential in customer E46 M3 LS swaps. This "large case" BMW unit is also used in heavier cars like the M5, 7 series, and more, and in the E46 M3 it always came with a limited slip differential.

The non-M E46 chassis got the medium case unit, and 100% of those were OPEN differentials, which while still fairly strong are not ideal for putting down power (I fight with the open diff with only 220 hp in my TTD 330). For this project the "easy button" solution would be to leave the E46 M3's larger 210mm ring gear unit in place and just upgrade the axles. And we proposed that to the owner of this car early on - but cautioned that the torque that this somewhat larger stroker LS motor can put out (700 ft-lbs) might be past the limit for this car. There are lots of BMWs running around making "dyno numbers" higher than we're shooting for on the 210mm housing, but I suspect many if not most are not making the torque we will. This will be a brutal track car that will even see some standing start launches (Optima Speed Stop events) on rather wide tires. "Over building" the diff was the smart choice...

continued below

Last edited by Fair; 05-19-2017 at 08:43 AM.
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Old 05-19-2017, 08:37 AM   #9
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continued from above

Here are more weights from the the 1999-03 Mustang Cobra 8.8" aluminum rear housing (62.9 lbs, at left) and the "medium case" BMW E36 housing (76.9 lbs, at right). The weight for the "large case" E46 M3 unit is above, at 100.4 pounds. All of these weights are complete housings with the factory rear covers, factory gears, and factory differential units. The BMW housings are heavier because they are cast steel - which is stronger than aluminum - but what usually breaks is the actual ring gear.

And while the external dimensions on the medium case BMW unit and the Ford 8.8" unit look similar, the 8.8" ring gear translates to 223.5mm. And this is one of those cases where "bigger is better". Not to mention there are countless ring and pinion gear sets available at a fraction of the cost of the limited number of BMW gear ratio options for either the 188mm or 210mm housings. And limited slip units are more abundant (and less costly) for the 8.8" vs the BMW units.

So like the engine and drivetrain in this build, we're looking at a domestic part for a lower cost and stronger differential, with more plentiful gear/diff options and a lighter weight by nearly 37 pounds.

We happened to have an 8.8" aluminum diff housing from a 2015-up Mustang S550 chassis, and its a thing of beauty. We mocked it up next to the 210mm M3 diff (above left) and it looked like it might work. Then we pulled the subframe out of the car, pulled it apart, and bead blasted it to raw steel. That's when we noticed - this S550 housing isn't going to ever fit. The front mounting "feet" on the S550 housing are inside the pick-up points of the rear suspension and the middle of the case hits at the back. This would require a completely scratch built subframe and new control arm lengths - and we don't need those kinds of hassles.

Enter the 1999-04 Ford Mustang Cobra aluminum 8.8" housing. I picked one up used because we couldn't find new stock of the OEM housing or even the old Ford Racing part number kit - popular with Cobra kit car builds for years. The M3 rear subframe was clamped to the fab table and Ryan started cutting...

The front of the 99-03 Cobra 8.8" housing is much narrower than the 2015-up S550 housing, so after some minor clearancing and reinforcement, the front was able to slide between the suspension pick-up points. The front sections needed a good bit of fabrication and even custom machined front mounting bushings, but it all went together smoothly. The centerline of the drive flanges was matched to that of the BMW unit and it was squared up before any of the mounts were designed.

The rear mounting was a bit trickeir. The 99-04 Cobra "clamp" mount was similar to the E46 non-M rear cover, but was never a popular choice and this cover/mount had failures in the Cobra Mustangs (below left). The later Explorer 8.8" rear cover (below right) mimicked the E46 M3 "ears" but they were in the wrong plane fore-aft and the wrong width. It was going to take massive modifications to make that work, so we punted on these.

Instead Jason recommended an aftermarket steel Ford 8.8" solid rear axle cover that has the same bolt pattern and shape as the 99-04 8.8" IRS housing. This was a fabricated unit for off road use, so it was beefier than the thin stamped steel OEM covers used on solid axle 8.8s.

It started out about 7 pounds heavier than the cast aluminum Cobra diff cover, which you can see above. But we needed thicker material to resist the torque of this LS motor, so the 1/4" thick steel unit was the right way to go. Buying a pre-made CNC laser cut and welded cover saved us a dozen hours of hand making this piece.

This bare steel cover was easy to modify to have "ears" attached that bolted to the E46 M3 rear subframe. Unlike the front, the rear mounting modifications were all done to the cover - nothing on the back of subframe was modified. Care was taken to maintain access for the rear cover mounting bolts as well as the existing fill plug.

The structure was set and plated, tack welded, then fully TIG welded to make a strong set of mounting ears on this 1/4" thick plate steel rear cover. Strong as an ox, yet compact. This cover came with a fill plug (threaded bung welded in, with a screw in plug) and we later added a drain plug as well.

The modified M3 rear subframe was also stitch welded to cover any gaps in the factory welds, just like the front. Then the rear subframe, the lower front mounting cross bar, and the reinforced front subframe were all powder coated gloss black.

So while the 210mm M3 diff housing might have worked, it was always going to be heavier, weaker, and have fewer & costlier options for gearing and LSDs. We would be having custom halfshafts built for either the 210mm BMW unit or the Ford 8.8", so that's a wash.

Aluminum subframe mounting bushings were installed into the shiny black M3 rear subframe. Instead of taking our chances with polyurethane or even Delrin, we're going "full stuff" on the rear diff and subframe mounts on this car.

We added a second threaded bung and plug to the diff cover before it was powder coated gloss black. This will allow us to run a dedicated diff fluid cooler, which will help keep the 8.8" unit happy under high torque abuse. The completed rear subframe - minus the diff housing - was installed in the car at this point to allow the rear suspension parts to be added.


The customer who owns this build is an avid HPDE driver who is used to high powered RWD cars, and now has the Miata track trainer that we built to hone his skills before he jumps into this V8 M3. Before the build began we asked him, like we ask all customers, "What class do you want to build for". This is crucial, as even simple parts choices made early on can limit where you can run any car. We don't ever want to build a car "just for track use" and always encourage folks to at least have some class in mind for "down the road". It tends to make any race car more valuable if it is legal for some class or series.

Wheel to wheel racing was never in the cards for this car, so we looked at places where it can compete in Time Trial - which still has a competitive thrill, similar contingencies, but only a fraction of the crash danger of W2W racing. For a car approaching 4 pounds per hp, there is one class you build for in NASA Time Trial: TTU (aka: Unlimited class).

I'm not going to delve into the intricacies of NASA classing rules for TT, but there are basically a number of classes based strictly on power to weight ratio (TT1/2/3/4), then a few remaining TT Letter classes that are both points based and p-to-w limited (TTC/D/E/F). Basically TTU is fastest, followed by TT1 to TT4, then TTC to TTF are further down the line. TTU will be a tough class to compete in because things like ALMS prototypes and open wheeled race cars are allowed there... but typically TTU acts as a catch-all class for cars that exceed the limits of TT1 or don't have their classing sheets or dyno sheets in order. It is still a rather large class in Texas, most of the time won by Paul Costas' GT1 tube-framed Camaro.

Left: I'm using the #JankyStick to point out duct tape. Right: Costas setting the weekend's fastest lap at TWS

With numbers around 2700 pounds with driver, "over 500 hp", giant 14" wide slicks with functional aero its going to be pretty hard to beat this car with a unibody BMW coupe chassis with roll up windows, but TTU is just where this car fits. See, I've already got the excuses ready if we lose! Paul is a good friend of mine and I'm sure he won't mind the "class filler" we will be for him. With 5 in class, a win in TTU pays 2 tires per day if you are running Hoosiers, and with 7 in class pays 1 for 2nd - so even a runner up finish might take home some tires.

For NASA TTU (and HPDE) the car will be run on 335/30/18 front and 345/35/18 rear Hoosier A7 tires, which we had exceptionally good results with in our TT3 car - this car was never beaten in class on these tires, and was easier to drive on than anything else we ever tested. These 345's are the widest DOT tires Hoosier makes, and should work well for this high powered car on the rear. We could possibly use a wider Hoosier 355mm racing slick, but I've found the DOT "A" Hoosier to be a bit friendlier, warm up quicker, and fall off later (more heat cycles) than dedicated racing slicks. I'd wager a very small amount of money that in the right conditions they are faster than similarly sized slicks. I might lose that bet, but in the first 1-2 laps of a TT session (the only traffic free opportunities) I've rarely seen any tire faster than A7s.

The more serious classing objective for this E46 CSL M3 is Optima's Search For the Ultimate Street Car series, run by the USCA organization. This is currently the biggest arena to showcase fast cars that have some smidgen of street car capabilities, with a massive variety of cars and a LOT of talented drivers and car builders. I have a lot of friends who compete in this series and missing the last 2 years of events is KILLING me.

We've had a modest amount of success in that series, where Amy and I have entered in Mustangs and Corvettes, and this BMW's owner ran a car at one event also - and enjoyed it a lot. I've always felt like they needed more BMW entrants in Optima, and I have been in contact with the series director to share our plans. Hopefully this hybrid BMW fits within their series parameters and gets as much TV time as our big heavy Mustang did.

Discussing the Optima series rules would take hours, but the basics are this: The USCA runs 8-10 qualifier events each year. There are 4 or 5 classes at these events, and the class winners from each qualifier get invited to Vegas for the "finale event" after SEMA, the Invitational. Here all of the classes get merged into one big shootout with 75-100 cars. Each qualifier and the Invitational are based on 5 competitions: autocross, speed stop, time trial, a road rally to test the streetability of all cars, and a judged car show section called "Design and Engineering". Winning a class at a qualifier is a big deal, as all of these events are televised. Winning the overall at the Invitational is a HUGE deal.

For this series the car has to run a 200 or higher treadwear tire, so we'll build around a 335mm front and 355mm rear street tire - which are the widest available/competitive tires. They won't be as sticky as the Hoosiers but we have some ideas to help manage that. We are building for the GTL class, but that's all I have to share about Optima classing with regards to this E46 M3 CSL clone at the moment. More soon!


In the next installment to this build thread we will show the electric assist steering we added along with the brake upgrades and suspension we have installed. Its all serious stuff that I am pretty happy with.

The max width tire and wheel testing will also be shown, which we used to order the first set of wheels. Then we will cover the unique rear seat mounted fuel cell and dry sump oil tank mounting we tackled for this build.

Thanks for reading,
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