So I am mocking up my high compression 306 build and decided to check piston to cylinder head clearance now that the pistons are sitting out of the bores a smidge. Head gaskets in place, heads torqued to 60 ft lbs I am seeing .033 read by measuring a cross section of smooshed clay. I have read that .040 is ok with steel rods, have also seen that .050 is the min. but that it really depends on piston side clearence and the bore size in reference in the pistons ability to rock in the cylinder at TDC. Thought about milling the pistons a bit in a friends mill but realistically head gaskets of about a .060 thickness vs the .039 I currently have would probably be better?

Thoughts?

 

i was tought that on the street you should have at least .100 clearence. but that was also on a big block

 

Read the the minmum for steel rods is .040 and aluminum rods is .060 for piston to head cleareance. That was from a dealer that sells Mahle pistons. Ptv clearance is nother issue that depends on the engine builder.

 

Sounds like what most quote for piston to valve, I havend checked that yet but I have a fly cutting tool and am using stock valves so it might not be a problem.

 

.033 is a little tight. You can do the math for it too.
Measure at the piston pin to the deck (or out of deck) and add the compressed basket thinkness = piston to head.
Thicker gaskets would be fine. Shoot for 0.040"+