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Lower compression

6K views 34 replies 8 participants last post by  MarcusLSB 
#1 ·
Im interested in lowering the compression of my 330ci 01 but cant find a way to do it. I know if i buy a thicker head gasket it would be lower but i would like pistons. Any advice.
 
#6 ·
The popular method these days is run 10:1 in either a SC OR a TURBO application. If you are fortunate enough to have access to E85, the high compression builds shine even more.
Builders and owners alike are finding great drivability from high compression build.
This does not mean low compression builds are dead. But this whole concept give owners and builders another option.
 
#8 ·
Larry from SP has stated on several occasions that a FI build with a high compression motor (10:1) works particularly well when run on E85. I dont recall the reason why, although I am pretty sure he did explain it Perhaps if you email him (he hates PM's) he might join the thread. I have asked him to do this in the past. It might have to do something with anti knock. Not sure.

I do know that everything FI works better on E85 including spool time, lowered temps and more. E85 is extremely desirable now days to run FI in the street and track. There are generally more costs involved setting your car up to run E85, so it is a fairly large commitment. The benefits can be astounding. There are Stage 1 HPF cars with no meth injection running mild E85 tunes putting out 630rwhp ALL the time...at 3.60 per gallon. You can run a lot more boost with E85 with no fear of knock. Limits usually surround the strength of your connecting rods.

A high compression build will also work fine on pump gas too.
The concept is that you will have much better throttle response, especially on the track for HPDE. A low compression motor just will not perform as well while it it out of boost.

I am not sure if it is even a good idea to consider E85 for a 330 motor. Possibly not due to internal component weaknesses. For the M3 s54 motor, yes, absolutely.
Most SC applications are left at stock compression. Turbo builds can be run at low or high compression on pump gas, race gas or E-85. The higher the octane or anti knock properties, the more boost and power you can make. This is also dependent on the strength of your internal components.
 
#10 ·
The M54 is a great engine to FI, you just need to keep the cylinder pressure low enough and the temps low aswell.

Bdave dont know what he's talking about , 10:1 is just .5:1 lower than stock.
Internal component weakness ? Really ? S52 crank and rods that are used in 10k rpm machines are weak ?
The harmonic dampener and oilpump are it's weaknesses.(And possibly the headbolts that strip the block if you overheat it)

What i would go for are raceware headstuds or custom M12 ones , a coopering HG and 9:1 pistons with eagle H-beam rods.
That setup should handle 30psi safely, run it on E85 and advance the spark instead of raising the boost(cylinder pressure still applies)

My 8.2:1 build without turbo keeps up with a stock 330, maby my tuning is better than stock but the power loss isn't that big.

Contact wiseco and have pistons made at your own chosen compression, contact vaio(some numbers) for an oilpump and start wrenching :)
 
#12 · (Edited)
You have not been keeping up with current trends here in USA. High compression Turbo builds of 10:1 (he said he needed new pistons, so order in 10:1) are popular right now. And its not ME talking, its Chris from HPF (Orange track car high compression turbo build on C12) and Larry at Sound Performance who advocates high compression E85 turbo builds.

I do believe those guys DO know what they are talking about. I am merely passing on their information.
The whole concept is not to LOOSE any more throttle response than is necessary when the car is out of boost. The higher you can keep compression, the better the car performs out of boost.
E-85 takes care of any knock issues and helps spool the turbo faster according to Larry from Sound Performance in Chicago. E-85 has a massive cooling effect and will help very much in keeping temps down.

If you have any questions, please address them to those two individuals.

There is absolutely nothing wrong with SweTurbo's approach, but there you will gain more throttle response by doing a high comp build. The car will have much better manners in HPDE say in exiting a turn if you happen (it happens) to not be in boost. The car will just be more fun to drive as a High Comp build. The M54 motor isnt the most powerful in the world so it can definitely benefit by keeping compression relatively high.


I suggest talking directly to Larry at Sound Performance in Chicago. His email is listed in his signature. He can explain your options a lot better than I can. With the right direction you can have a very serious build that runs circles around other conventional low comp builds.
 
#14 ·
What is your power goal Edgar. That's probably the most important question to ask when determining your ideal compression ratio, close second to that being how available is premium fuel to you (be that E85, C16, 110L, etc)... if you raise the compression (or stick to your stock 10.5:1) you'll net smaller numbers on pump gas but yield a better curve on race fuels such as those mentioned above.
 
#16 ·
What do you plan on running for an ECU (have you got that far yet in planning?). If E85 is relatively available to you I personally would run the stock 10.5:1 compression ratio and tune the car to the lowest blend of ethanol you typically see in your area. Maybe thats 70%? Ethanol is a VERY capable fuel, and even on probably 40% ethanol you'd have no problem making 400-450rwhp on a turbo'd M52. You'd want to likely redo your fuel system from front to back, including uprated pumps to support the additional flow needed for E85. Some would say you're fine using existing lines and just installing an uprated pump.. which is probably true as well but that depends on your budget.
 
#23 ·
That would depend on turbo size (assuming turbo) amount of boost predicted and estimated RWHP.

I found Areomotive tech department very helpful in calculating flow of E85 needed (in pounds per hour) for builds with known turbo size, known boost and and estimated RWHP. Their calculations help determine fuel pump requirements and injector flow requirements.

A rough (as in not exact) rule of thumb is that for the same RWHP that you would get using gas or race fuel, you must enlarge everything by 33% to flow the amount of E85 needed. This has to do with BTU's and efficiency.

This would be a good time to start doing some serious RESEARCH (as in SEARCH, GOOGLE etc) on the subject of using E85 for forced induction (primarily turbo) applications.

The benefits are numerous...cooler, less soot and deposits, cheap per gallon costs, faster spool time. Race gas type power available ALL the time at pump gas prices!

E-85 does not come out drawbacks too..harder to store, water absorbing qualities, larger flow hardware needed, and so on. Time to do some heavy reading I am afraid. There is tons of information on this forum, other forums and the web.

Some guys (in Canada) like E85 so much that they will drive 12 hours in a rented truck just to purchase and transport drums (months supply) of E-85 in the closest areas of availability. Some of us (CA and FL) are lucky to have E85 readily available and close by. Good Luck.
 
#28 ·
So I'm running Bosch green top injectors 42lb i think thats 440 cc
Im thinking of going up to 600cc to make the same hp that im making now in my head it makes no sense. My goal is 420 rwhp more or less so i will be going 1000cc is this reasonable
Here you go :
http://www.gtsparkplugs.com/InjectorSizeCalc.html

E85 will give you more power so just saying that 30% plus to make the same power is incorrect :)
 
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