Lower compression

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.

Unless you have FI there is No reason to lower compression.

My car is supercharge but im thinking of changing to turbo don't know yet.

What exactly are you wanting to do with the car? Are you building a motor for drag racing ,track racing ,or for the friday night downtown drives?

Track / sunday night
Dont know it these two conflict with each other but i thinks its possible. I had a mx-5 turbo that gave me both functions. I do know no drag racing thats just stupid

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.

I do have access to e85 but could you explain I've never used this fuel. How would this help me I'm lowering the compression or how would it benefit me

Originally Posted by Edgar3498

I do have access to e85 but could you explain I've never used this fuel. How would this help me I'm lowering the compression or how would it benefit me

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.

Originally Posted by Edgar3498

I do have access to e85 but could you explain I've never used this fuel. How would this help me I'm lowering the compression or how would it benefit me

The main technical issue with FI and compression is that as you increase boost, fuel/air temperatures increases _during_ the compression stroke. If those temperatures raise too much, the fuel/air mixture will undergo combustion prematurely. Under WOT and full boost, these unwanted occurrences, called detonations, can damage an engine very seriously.

There are several ways to reduce or manage conditions that lead to detonation. Lowering compression is the more drastic of such methods. What is best for you want to do depends on what you want to do and how much money you have to reach those goals.

The most obvious solution is to use a fuel that has a higher octane rating (detonation resistance) such race fuels like 110 octane race/aviation fuels, C16 or E85. Some problems are cost and general availability of the fuel but it's probably the easiest path to running higher boost.

Water or methanol injection can help lower pre-combustion temperatures and/or raise octane levels as well but require significant design consideration of the delivery system. It's best to install these types of options with a kit because the exact application needs to be tuned. With a kit you don't need to start from scratch. I view it as a band-aid approach the problem but it's a nice next step for people who want to fiddle with those types of setups.

E85 is more convenient because it's less expensive than race fuel and more available but it requires that parts of the fuel system be upgraded, rubber components might need attention since some components made of lower quality materials will degrade and fail. E85, as a fuel, has a lower power density than gasoline; so you will need to inject more fuel to burn an equivalent amount of air.

Regardless of the exact fuel, if your motor is consuming more air, it will require more fuel, so you probably will be looking at injector and fuel pump upgrades depending on your goals and the capacities of the components your car has.

The most drastic method is obviously an engine rebuild for lower compression. That's done either by replacing the pistons with a model that has more dish, using a thicker gasket or even removing material from the head.

Overall, boost can be considered to be another form of compression. Between the boost and cylinder compression, and a few other factors relating to intake air temp etc, there exists a compression limit where temperature increases will cause fuel to burn spontaneously. That limit relates to the octane levels of the fuel you are using.

I hope that answers your question.

Why is that my engine would not cope well

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

Originally Posted by SweTurbo

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

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.

Originally Posted by Bdave

The main technical issue with FI and compression is that as you increase boost, fuel/air temperatures increases _during_ the compression stroke. If those temperatures raise too much, the fuel/air mixture will undergo combustion prematurely. Under WOT and full boost, these unwanted occurrences, called detonations, can damage an engine very seriously.

There are several ways to reduce or manage conditions that lead to detonation. Lowering compression is the more drastic of such methods. What is best for you want to do depends on what you want to do and how much money you have to reach those goals.

The most obvious solution is to use a fuel that has a higher octane rating (detonation resistance) such race fuels like 110 octane race/aviation fuels, C16 or E85. Some problems are cost and general availability of the fuel but it's probably the easiest path to running higher boost.

Water or methanol injection can help lower pre-combustion temperatures and/or raise octane levels as well but require significant design consideration of the delivery system. It's best to install these types of options with a kit because the exact application needs to be tuned. With a kit you don't need to start from scratch. I view it as a band-aid approach the problem but it's a nice next step for people who want to fiddle with those types of setups.

E85 is more convenient because it's less expensive than race fuel and more available but it requires that parts of the fuel system be upgraded, rubber components might need attention since some components made of lower quality materials will degrade and fail. E85, as a fuel, has a lower power density than gasoline; so you will need to inject more fuel to burn an equivalent amount of air.

Regardless of the exact fuel, if your motor is consuming more air, it will require more fuel, so you probably will be looking at injector and fuel pump upgrades depending on your goals and the capacities of the components your car has.

The most drastic method is obviously an engine rebuild for lower compression. That's done either by replacing the pistons with a model that has more dish, using a thicker gasket or even removing material from the head.

Overall, boost can be considered to be another form of compression. Between the boost and cylinder compression, and a few other factors relating to intake air temp etc, there exists a compression limit where temperature increases will cause fuel to burn spontaneously. That limit relates to the octane levels of the fuel you are using.

I hope that answers your question.

Did not read the rest of the thread to see but this is information worth quoting

Originally Posted by wtbass21

Did not read the rest of the thread to see but this is information worth quoting

One of my better ones, I agree. Thank you.

I just want to emphasize that the experts like Sound Performace say the best bet for FI is a high compression build run on E85. Whether or not the build needs new rods or forged pistons is up to the builder, taking into consideration max boost and HP, and generally accepted limits of the OEM components.

Ill research that but my question is can i run e86 on my car safely and what modifications would i have to do

Thanks i will

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.

Power wise i would like to hit the 400 450 somewhere over there with stock internals if possible. I will make a bulletproof bottom end but if i can achieve this with stock internals i will be happy. E86 is very accessible to me

Originally Posted by Edgar3498

Power wise i would like to hit the 400 450 somewhere over there with stock internals if possible. I will make a bulletproof bottom end but if i can achieve this with stock internals i will be happy. E86 is very accessible to me

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.

Originally Posted by MarcusLSB

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.

To OP: Exactly what Marcus says. Note the point I forgot to mention. Pump gas figures suffer a bit on a high compression build, but E85 will yield you untold bounty in so many ways.

Note also Larry from SP's post about how even stock compression on OEM BMW turbos is now 10.5.

At this point you should see some fairly compelling evidence for doing a high compression build. If you can commit to E85 in the manner that Marcus suggests (safe), you will have one of the better (best?) 330's around.

An optional but quite nice electronic item is a gauge that will simply read out your current ethanol content of what ever is in your tank. It is always good to know for sure.
http://www.gtfabrications.com/product.php?productid=850
Shop around for best pricing. An expensive, but handy option.

Also: "re do fuel system front to back" likely means needing larger injectors when switching to E-85 and FI.

You can start a "build" thread when you decide on a direction.

Good luck!