914-4 2.0L approx. 10.5:1, JE forged 2618 Aluminum pistons, Web 163/86b cam

JE clearance guidlines say to set clearance to .0035" along with a note "some applications may require more clearance".


I had cyclinders bored 0.75 mm oversize with piston clearance of 0.0035", but am having second thoughts; maybe should of increased clearance to .0045.


Engine will see road racing conditions, so will get run hard for 20-30 minutes or more during each race. Should I increase the piston clearance? I'm assembling the engine now so it's not too late to address.

Thanks,
Jim

Any thoughts before I assemble this engine? I checked the clearance of each piston/bore, and am going to put largest of .0038” in # 3 position.

Thanks again,

Probably not too many engine builders looking in this forum on a regular basis, Jim.
I bet you would get some opinions if you posted the same topic in the Garage.

Len Hoffman...(HAM inc.)...advised me when I put JE's in my 2316....I advise you to PM him before you increase that clearance.....as I recall he said not to exceed .0025", so you're maybe past that already....

FWIW, I just finished building a 911 six. I used Wayne Dempsey's engine build book a he recommends 1.5mm clearance for intake and 2.0mm for exhaust.