so i am building my 383 it is almost done. i had 2 problems with diamond pistons and are very unhappy with there product. 1st diamond problem was that all the pistons weighed 18 grams from each other. 2nd problem is that on the new batch they cut the oil groove or something to far my builder said. i also noticed when i was at my machine shop that they didnt send the original pistons i ordered. i originally had -7cc pistons and now i have ones with valve reliefs. so if i have 64cc heads and -2 cc valve reliefs my compression would be around 11.4 is that safe to run on 93 octane? also my cam is a 240/256 mid 640 lift cam would this clear without flycutting?

 

11.5 and that cam is more than fine with pump gas. You should always clay every setup.

 

I would check especially if its a custom combo (i.e. not stock GM). I did not do PTV as my cam was on the smaller side and nothing short of big custom cams or a MSX, or TRex would I be checking.

Pump gas should be fine, there are other varibles but you should be mint!

 

If your combo includes the 317 heads from your signature, milled down to 64cc's, that's roughly .050" removed, which leaves .050" less PTV. I would definitely degree you cam, then measure your clearance.

 

i sold those heads. i am going to get either stock 243s or ported 243s not milled

 

what size valves are you running?

 

You should be fine with that compression on 93 i run 11.7.1 just work with the tuning, also your engine builder should be able to check valve clearance and quench, you want to have at least .100-inch on either valve.

And for absolute assurance also recommend that you check at all points for ten degrees on either side of TDC, Cause the closet proximity may occur at a point just before or after TDC, depending on the phasing of the cam in relation to the crankshaft. Good luck on the build.

 

stock ls6 valves

 

What he said!

 

well he is just building the bottom end. i am doing the cam/heads install to save some money. do you guys think there is a possibility it would fit with stock ls6 heads? also what is the best method to check for PTV clearance

 

You have a decent shot since you are running unmilled heads with stock sized valves. You can measure the drop with some checking springs, but you may be better off measuring clay thickness to determine the radial clearance at the valve reliefs in your pistons.

Anyone who tells you "it will work" doesn't care if it clears for you or not. Too many variables from engine to engine, even if they have run the same heads and cam on a 383.

 

thanks for the input! i was just getting everyones opinion but im still going to measure just to be safe. what do you think is the best way to measure and would there be a in detailed write up on this?