Wtb m20 b27 euro spec pistons

[ForcedFirebird]

Maybe. The valve reliefs are deeper because the pistons are higher compression, and BMW left the valve pocket depth the same (in relation to the cylinder head).

Since you shaved the block, you brought the pistons back to factory compression height, so all should be very close to factory limits. Your cam would be the deciding factor, and shaving the block backs the cam up a few degrees, so an aftermarket cam should be checked for VTP clearance. If you need more room, use an adjustable cam gear.

[Ceeker]

Thanks again for your input and time..I have a stock head with gasket going to install and check for possible binding. The 284/272 cam will be used for my set up.
I guess I'll find out.

[Ceeker]

Maybe. The valve reliefs are deeper because the pistons are higher compression, and BMW left the valve pocket depth the same (in relation to the cylinder head).

Since you shaved the block, you brought the pistons back to factory compression height, so all should be very close to factory limits. Your cam would be the deciding factor, and shaving the block backs the cam up a few degrees, so an aftermarket cam should be checked for VTP clearance. If you need more room, use an adjustable cam gear.

Sorry to sound redundant..

Valve reliefs: The exhaust side is physically larger on the new pistons but I don't see much if any with the intake side.

I just realized I have b25 9.4:1 pistons identical to the 8.8:1 NA pistons. and I decked the block 70 thou. I installed the head with a stock cam to test for interference but didn't get any with a stock new gasket.

When the head is off the the crown of the piston sits about 1mm above the block deck. I did this to increase the compression.

So to clarify: Im no math wizard by any means and all these numbers are making my head spin.

I did notice the 256 stock cam has a intake/ex lift of 10.1mm

The cam I am looking at -Schrick 284/272 has an intake lift of 11.4 and 11.0 exhaust.

Will the slight difference in this measurement be a cause for concern if I am using an adjustable Cam gear?

[ForcedFirebird]

Correct. The valve relief bottom (the "blind hole" if you will) has the same plane on both pistons. In other words, if you stick either piston in an engine, you will have the same valve to piton height. To get the added compression, BMW had the rest of the piston raised into the chamber, thereby causing the reliefs to appear "deeper" even though they have the same bottom plane in the notch.

When you say "I raised the piston 1mm", not sure what that means. But, since you have about 1mm between the piston crown and the chamber squish band, if you raise the pistons 1mm, they will surely contact the head itself at the squish band - the valves aren't even a concern at that point. The compression comes from the size of the dome, the m20 doesn't take well to just popping the piston out higher since the squish band is angular and there's not much room to play with - this is why the 885 head has a "max shave" limit, the piston contacts the head long before the valves hit the pistons.

Put the head on the block, bolt it done with old head bolts, install/time the belt and use something to pry the valve open when the piston is at TDC and you will see your PtV clearance (or use clay/solder to test). Basically you are shooting for +.040" (+1mm) clearance from the piston to the head, .080" (2mm) for exhaust valve clearance and .100" (2.5mm) on the intakes. I have a local client with about 5yr driving his 216whp m20b28, and that engine has .037" quench (piston to head), .057" exhaust and .073" intake, no issues with a 272 cam and 7200 limiter, even with the new OEM springs.

[Ceeker]

thank you for the response; I had to read this over a few times for it to sink in. I understand what you are saying now. With that said.

Chamber squish band

I suppose a stock head gasket wouldn't compensate for this deviation in space so I'd need a thicker head gasket?

PTV clearance

With the thicker head gasket; id create a bit more clearance for the valves and also having an adjustable gear would help?

I didn't start with a stock head gasket and bolts but I do have a spare new VR head gasket I can use and see what kind of result I'll get with
the solder test.

When you say bolt the head down and pry the valve open I will assume there is no cam or rocker bolted on?

Do I just take some solder wiring snip off a piece and place it on the valve reliefs before tightening the head down? then rotate the assemble
twice over. Then use callipers to check the solder thickness?

thank you.