Quick summary

[kylebes1]

After reading through the m20 stroker threads for the last hour, and being on the clock to do it :twisted: , here is what I come up with, but I need to be sure.

I can deck a b27 block and use an "i" head. This will produce over 9:1 compression if done to the proper extent. <---- Does any one know exactly how mush to take off if I want exactly 9:1 CR?

:Edit, I am rebuilding the engine's head and bottom end, so I will have proper stroker.

[screamingbmwe30]

dont waste your time. get a 323i head and some european early eta pistons 10.?:1. high compression stroker torque monster and factory "hot" cam. just throw the 325i motronic and 17lb/hr injectors and be done

[kylebes1]

dont waste your time. get a 323i head and some european early eta pistons 10.?:1. high compression stroker torque monster and factory "hot" cam. just throw the 325i motronic and 17lb/hr injectors and be done

Thanks for the advice.

I already have the "e" bottom end and the "i" head so I would like to just use them.

[Madhatter]

More than you could do without messing up cam timing.

If you want to fix the compression ratio buy a new set of pistons.

[kylebes1]

Can I go with longer connecting rods as well? I read a lot about rod ratio, I am sure there is room for improvement, but is there space for longer rods?

[Madhatter]

i surpose you could, you would need to measure piston crown to deck clearence. But seriously, a set of rods is going to cost you more than a new set of pistons.

[SA E30]

I would really be careful with running longer rods, cause it's really easy to get the rod ratio out of whack.

Rather get some custom pistons, if u gonna wanna use custom parts to raise the CR.


BTW I run a 328i crank, on M40 318i rods, and S50B30 M3 pisons (86mm). It's a nice and tourqey motor

[kylebes1]

I would really be careful with running longer rods, cause it's really easy to get the rod ratio out of whack.

Rather get some custom pistons, if u gonna wanna use custom parts to raise the CR.


BTW I run a 328i crank, on M40 318i rods, and S50B30 M3 pisons (86mm). It's a nice and tourqey motor

What displacement does that produce? and does the engine have to be bored over?

[Madhatter]

well it is an 84mm bore factory, so what does that tell you? 8)

[kylebes1]

thanks, learned something today.

I would guess that takes you to 2.8 liters?

[Madhatter]

the first rebore pretty much does.

[Jarvis]

thanks, learned something today.

I would guess that takes you to 2.8 liters?

I think the 2.8 is 84mm x 84mm from the factory... add 2mm to the bore...

[kylebes1]

thanks, learned something today.

I would guess that takes you to 2.8 liters?

I think the 2.8 is 84mm x 84mm from the factory... add 2mm to the bore...

Yep, 84x84 makes like 2.79.

So if I go to 86mm pistons that is... 2.92.

Is 86mm as high as it can go?
86.5 bore makes 2.96 L
87 bore makes 2.99 L

If you can get 87mm pistons in there I you could have a 330is !!!

[DrMcDave]

87 is too much.

you can use a s52 crank and rods and custom pistons to create a 3.2 m20. metric mechanic has done - 1 and only one. But it can be done. the guy build it himself and messed up the piston rings but i was told to expect 240+ hp. i have a some s52 rods if you would want them for any reason let me know.

[kylebes1]

I have all teh time in the world, to do this.

so can you go with 86.5 mm bore?


Are the m52 cranks and m20 b27 cranks the same stroke? Is there advantage to teh m52 crank (if they are teh same stroke) other than being forged? I am looking to s/c it to make 300 whp, so that means about 350 crank hp. I thnk that is do able with 2.9 L and 7 or 8 psi. Would the cast crank of the m20 be strong enough?

--Setp off question, will a s/c m20 make power past 6k rpms with a mild cam as well>?