m20 stroker (using m51d25-e36 325td)

[harry02]

Thanks man , will play with those number.

[harry02]

The piston is 1.1mm below the top of the block , piston dome is 3.792cc,

@digger how much do you think i need to take for 10.8:1 compression ratio (95octane gas available other here) ?

[digger]

The piston is 1.1mm below the top of the block , piston dome is 3.792cc,

@digger how much do you think i need to take for 10.8:1 compression ratio (95 octane gas available other here) ?

Do you have 9.7:1 pistons? if you take 1.1mm off the block that gets you 10.6:1. my previous numbers were based on 9.4:1 pistons but i misread.

you might be able to take a bit more like 0.10 to 0.20 mm extra off block to give you 1.20-1.30 mm total from the block if you check piston to head squish clearance (aim for 1.00-1.10 mm) this should get you to 10.8:1. or you could take 0.20 mm from head

what is special about 10.8:1? a difference of 0.2:1 will be imperceptible for power and torque

is that 95RON? thats about 91 PON in the USA. if it is i would not try for 10.8:1 with that fuel, more risk for knock for little gain.

[harry02]

yes i have 9.7:1 piston ,yes RON 95 - MON 85–86 - AKI 90–91

10.8:1 is what i think is the maximum CR for 95 octane pump gas other here, i just try to get most hp for my build, but i take your advices and just mill it to -1.1mm .

I try to fit in a class rule where its dominated by vr6 12valves engine , (rules : 2v engines - max : 2799cc )

[digger]

if you use more camshaft duration you can run higher compression but you might want a better ECU than stock

[harry02]

i will use another camshaft after few months of the rebuild, as i plan to stay naturally aspired , maybe a WAR MAF and chips later.

[Armichy]

Sorry to hijack this thread, but i'm also planing to stroke my m20 with an m51 crank, in my case it's an m20b20.

The idea is to use as i said, the m51 crank, m52 pistons and rods,shaving the crown about 2mm and cutting valve pockets(free of charge, courtesy of my friendly machinnist at work), and unfortunately i'm stuck with the stock 200 head, currently im reading up on the whole port and polish deal, but i figured since m52 pistons are flat headed(or will be once im done) and the m20b20 are also flat, i might be ok.

Bear in mind this is a REALLY low budget build