E30 Zone

I have an m44 engine that I basically want to extract more power from, and have been looking into stroking it using the m47 crank etc.

What I am having trouble getting my head around is compression ration and piston heights etc, as I am not very sure about what is needed.

What I want to achieve is to increase the displacement of the engine, as in the long term i want to go FI with the project, and, please correct me if i'm wrong, a larger displacement should yield a better response from FI?

However I do not want to raise the compression ratio too high with this in mind, as I am planning on building the engine up with forged parts to replace the cast rubbish that lives in there atm, so dont want to have to take it apart again in a years time to lower compression.

So, say I have the m47 crank 88mm stroke and a bore of say, 86 or 87mm, can I then use something like the MM pistons to lower the compression? Will this give the desired effect or have I just got the wrong end of the stick?

Sorry for my complete lack of knowledge on this

NOTE - NO ENGINE SWAPS! I WANT A FOUR POT

Forged pistons would be the best way, although you could keep the standard pistons and decompress by using a steel head gasket, or get the stock pistons ground.

And good man for sticking with the 4 pot wrongness I might have found an M44 for peanuts that (if I get it) I plan on building a hybrid M42/M44 turbo thing.

I expecting to see a mayonaised m20 engine

Yeah sorry about that - read the title back to myself and realised that may be what alot of people were expecting!

I will be using forged pistons and rods for sure, the issue is the crank is cast on m44, wheras if I use m47 that is forged, so will be more robust. I am unsure as to whether I will have to get custom pistons/rods made up, and how much it would affect compression.

For instance, if I have 88mm stroke and 86mm bore as opposed to standard 85, I believe I read somewhere this gives 11.5:1 comp ratio (think thats written right!) Now that will be way too high for FI, even if I could get it down to stock comp (which I believe is 10.0:1)
I could at least run a low boost application, but have a solid engine.

Can this be done by getting the pistons ground? Am I along the right lines? Sorry to be such a noob on this!

Jon_Bmw wrote:I expecting to see a mayonaised m20 engine

+1

I can find a pic of one if that makes you feel better

Yes please

I expecting to see a mayonaised m20 engine

am i the only who held onto the vain hope that his actual head had exploded

sorry mate its nothing personal im just a kid at heart

No offence taken mate - although someone somewhere must know how to increase displacement and at the same time lower compression - I tell you what, I'll trade a pic of my head exploding next to a mayonaised m20 for the answer!

just me then though....

sorry i cant help you though mate