Hey there guys, been around on the forums for a longg time now and im working on another 305 motor for my new 86 z28 that I have. Ive got a few questions about which headgasket to use on my 305 build that im doing. Looking for some technical data, as most of the 305 gaskets ive found dont list a bore diameter or compressed thickness in their descriptions?

The only 305 application headgasket ive found with the data I need is the mr.gasket one #5780G which is a .028 compressed thickness with a 3.87 bore diameter. My problem is most of the performance (thin) headgaskets ive found are all a 4.1xx bore which I know is too big. I have the block decked so the piston is .012 in the hole and the heads are milled to a 52cc. Im trying to keep quench tight on the motor, thats why im concerned on the gaskets. Has anyone used the felpro #8510PT? What is the diameter and thickness of that gasket? What do you recomend?

 

If the pistons are .012" down in the hole, the .028" compressed gasket would be perfect.

 

Im sorry I actually just re-read what I wrote and realized I mis-typed it. I was at work and in a hurry when I wrote this up. My piston is .010 in the hole. And I also did a little more reading on the #8510PT felpro gasket, its looking like those are .039 compressed thickness. They are aso more readily available. Which should I go with? Was hoping some of the old 305 guru's (mw66nova, FAST355) would chime in....

 

the last gaskets i used before going lsx was a steel shim head gasket. had a 4.1" bore if i remember correctly. it was like .016" maybe. if you can find a .028" gasket i'd imagine you'd be OK even if the bore is a little big. the motor is actually still together with no signs of detonation, even at 10.5:1 with iron heads and 40* locked out timing. run 93 octane and it should be a-ok