Lowering Compression on m50b25 vanos

[kyleM50 0]

Is anyone running standard bmw engine parts to lower there compression? I was looking at using the pistons from my m50b25 tu and crank and using the m20b20 rods, I have seen bits here and there but no cars running them is this something you guys run?

My other option is to run a copper spacer and athena cut ring gasket. I would rather not run a spacer but if its the best route to go other then forged internals thats what I'll do.

[polley 916]

Depends whats your budget is and what you're trying to achieve.

[euroriffic 595]

I was looking at running a cometic mls gasket that was about 3.5mm and dropped compression to about 9-9.5.

[handgrenade 189]

what is the standard compression ratio? for forced induction, you can do great things with high comp/standard comp engines. of course if you want to push large numbers, best to go forged .. gives you extra head room if your tune/fuel/something goes a little off.

[mops 4]

Depends on your goals and budget.

you can start developing on what you have and change later. If I was doing a turbo project i would do it as follows:

Phase 1: This would work to low boost 6-8 psi - hard to say exactly

-add turbo - large exhaust housing will reduce detonation therefore allow more psi but will result in slower reponse

-new exhaust manifold - fancy low restriction with individual branches will reduce detonation (i.e. more power)

-new exhaust

-intercooler

-slightly larger injectors

-RRFPR

-wideband oxygen sensor with display

-optional tune by adjusting MAF

-optional for drivability turbo chip or custom tune or piggyback of some sort

-optional meth injection (given its low cost I would always consider if for safety and additional power reasons)

-at any point i would recommend standalone EMS to get maximum drivability out of your setup

-at this point you will need a LVV cert

Phase 2: this should get you to 8-10 psi on factory internals

-larger injectors

-mandatory: tune,

-at this point stock EMS might not be sufficient therefore some form of EMS will be required - piggyback or map conversion or whatnot

-i would definitely consider standalone EMS at this point which will allow you to maximize power and drivability, anything less will result in some compromises.

-with meth injection and good tune you might get a bit more than 10 psi, given good fuel quality.

-with standalone EMS you will be able to run more boost and therefore get more power on race or AV gas or some other high octane additives (toulene )

-at this point you can try thicker headgasket, it might get you a little further.

Phase 3: this is where you need to strip the engine and replace components. specifics this will depend on the goals and budget. Phases 1&2 can be done cheaply if you know what you are doing but this will require more $$$ because machining and custom parts are expensive (think thousands of $$$)

[handgrenade 189]

Depends on your goals and budget.

you can start developing on what you have and change later. If I was doing a turbo project i would do it as follows:

Phase 1: This would work to low boost 6-8 psi - hard to say exactly

-add turbo - large exhaust housing will reduce detonation therefore allow more psi but will result in slower reponse

-new exhaust manifold - fancy low restriction with individual branches will reduce detonation (i.e. more power)

-new exhaust

-intercooler

-slightly larger injectors

-RRFPR

-wideband oxygen sensor with display

-optional tune by adjusting MAF

-optional for drivability turbo chip or custom tune or piggyback of some sort

-optional meth injection (given its low cost I would always consider if for safety and additional power reasons)

-at any point i would recommend standalone EMS to get maximum drivability out of your setup

-at this point you will need a LVV cert

Phase 2: this should get you to 8-10 psi on factory internals

-larger injectors

-mandatory: tune,

-at this point stock EMS might not be sufficient therefore some form of EMS will be required - piggyback or map conversion or whatnot

-i would definitely consider standalone EMS at this point which will allow you to maximize power and drivability, anything less will result in some compromises.

-with meth injection and good tune you might get a bit more than 10 psi, given good fuel quality.

-with standalone EMS you will be able to run more boost and therefore get more power on race or AV gas or some other high octane additives (toulene )

-at this point you can try thicker headgasket, it might get you a little further.

Phase 3: this is where you need to strip the engine and replace components. specifics this will depend on the goals and budget. Phases 1&2 can be done cheaply if you know what you are doing but this will require more $$$ because machining and custom parts are expensive (think thousands of $$$)

each to their own and it sounds like your plan may work .. but I would disagree with some of that ..

any engine, even with forged whatever won't live long with detonation and/or preignition.

one of the best things you can do (what I consider most important) is get your fueling right.

the first thing I would do is to make sure you can adjust the timing and fuel. (ECU)

then make sure your fuel system is capable to support the power youre after, and even some headroom. (Injectors, Fuel Pump)

then build all the usual turbo bits .. manifolds, intercooler, turbo etc.

Then using a wideband o2 and a dyno, get it tuned. If you're running high compression factory engine, keep the on boost mixtures on the rich side. I would also suggest dropping the rpm limit a little.

if you think of the components in your engine, high rpm = stress on your small end bearings and tension forces in your rods.

increased fuel and air on the combustion cycle = compression stresses on your rods

most rods are strong in compression (they are relatively short, and have a high i value).

bearings may let you down if your oil system is not up to it, or if you run into high temperatures.

keep the temps down, fuel/air safe and your revs sensible and a lot of n/a motors will handle a lot of power with standard internals. rb25de nissan engines seeing 300rwkw in d1nz drift machines for an entire season, sr20de engines running daily 260kw etc etc.

so once the basics are done, the progression is easy:

if you want more power, put in more fuel and air. if increasing the amount of air means driving the turbo outside its efficiency range (hot air) then it is time for a larger turbo (hotside at least). keep adding fuel and air (larger injectors, re-tune). you will reach a point where either previous/inherent weak points in the engine will break under the increased load or something like a bad batch of fuel or a hot day or a popped vac line leading to overboost or oil starvation under hard cornering etc etc etc will grenade your engine. my money is on bearing failure of some sort which will lead to that eventual death ..

anyway its all anecdotal. you could do everything right and it could go bang on your first drive. or you could hack it together and run safe for ages.

everyone on here will have a different opinion about how to do it.

[mops 4]

I would agree definitely agree that having standalone ECU would always be a great idea at any stage as soon as some modifications are introduced. There are however ways (piggyback/chip tune/mapecu/warchip/etc) that would allow low amount of boost on stock ECU (no hard rule here but lets just say 8psi).

Fundamentally as long as the engine is not detonating its not going to fail provided other maitenance is in check (eg. good, clean oil)

Normally driven street engines dont die - given good maitenance enenvtually rings and bores wear out resulting in high oil consumption and low compression whcih in turn leads to low power and blowby and poor fuel economy, etc.

HIghlt stressed competition engies die because some of the components have physically failed, ie. crack pistons/ringlands/rings/head/HG (typically detonation, but otherwise thermal overloading), rods (typically overreving or lubrication)

At low boost levels I would not worry about oiling problems unless some engines are prone to such issues (bmw m5x engies do not apply here). reving high is much more stresfull to the engine than low-moderate amounts of boost. FI engines make power by applying similar amount of pressure to the piston for longer time during the stroke, whereas NA engines make power by means of incerasing peak cylinder pressure.

Again it comes down the budget and the goals. Daily driven low-moderate boosted engine can be done with stock internals relatively cheaply. Longetivity depends on how it's driven. Surly for serious competition purposes other provisions have to be made to make it last. Did I mention budget and goals ?

[No name user 379]

my .0002 cents worth

my m50 runs 12 psi stock compression on 91 octane, see's full boost at 4k which isnt an issue i spin it to 8200

runs pretty big cams 228@.050in 238@.050ex

runs autronic ecu

breaks the 245's loose topend of 4th gear

point is no detonation no decomprssion running thick head gaskets isnt a good idea

this is on a stock bottom end the good motor has yet to be dropped in and will do so once the 6 speed and upgraded rear end goes in

as has been mentioned each to there own