Tech Check - Piston Deal Compatibility

r3dn3ck · Feb 11, 2024

SRP 271106 They're flat top 3.572" (+.020) with 2v fly cuts. 4032 alloy like I wanted. The set of 8 is 450 bucks previously owned but still brand new/unused/in-box. I would super dig saving 500 bucks on pistons. Thoughts from the hive mind?

The fly cuts amount to -3cc so I think it might punch the CR down below 11:1, around 10.5:1 which isn't ideal but I can live with it. I like the 1.2/1.5/3.0 ring package better than 1.0/1.0/3.0. It's the right alloy, the right bore size, they're pretty light. The 2v fly cuts should matter not one bit as far as I recall other than dropping the CR a tit.

If I'm being stupid and cheap, say so.

lwarrior1016 · Feb 11, 2024

I guess that would come down to piston to valve clearance, and depend on what cams you were going to be running. If you’re running big lift or being aggressive when you degree them, you may need valve reliefs. If not, I’d run them.

r3dn3ck · Feb 11, 2024

For cams I won't be going nutty there, just enough to allow shifting at 8k rpm but peak should be around 7k. So probably not needing much more lift but definitely a spring upgrade and lightened locks and keepers. Duration will go up and LSA will probably decrease marginally if I remember my cam spec fundamentals properly but it won't be radical on the cams at all. The one thing I miss about using Windows is I had a copy of Desktop Dyno that was pretty helpful in figuring out these kinds of things. But... looks like it's not a terrible idea. Can anyone confirm my napkin math on the CR?

96blak54 · Feb 16, 2024

The valve reliefs are a bonus. Any off the shelf cam for a pi head will be fine with a .070" deep valve relief on the intake side when using stock valves. The stock intake valve has a super thick margine overhang. If you can and the budget allows for it, install bigger aftermarket intake valves. Doing this really wakes up the pi head. There is plenty of seat material for a 1.840" intake valve. Cutting a new 3angle seat for the new valves opens the I.D up considerably. IIRC its in the area of .150". Plus the new valves dont have the over hang margine interfering with piston contact and they are much lighter, not needing a heavier aftermarket valve spring. All that said, a bigger valve is a good move if you are maximizing potential.

With 1 valve relief, .045" felpro crushed head gasket with a bore diameter of 3.600", 3.572" piston, pi head 42cc, you are right under 12.1 static compression. This is all assuming the piston is zero deck and no block decking machine work or no head decking machine work.

Swapping to an aftermarket intake valve will increase chamber cc's as well.

96blak54 · Feb 16, 2024

lwarrior1016 · Feb 16, 2024

96blak54 said:
The valve reliefs are a bonus. Any off the shelf cam for a pi head will be fine with a .070" deep valve relief on the intake side when using stock valves. The stock intake valve has a super thick margine overhang. If you can and the budget allows for it, install bigger aftermarket intake valves. Doing this really wakes up the pi head. There is plenty of seat material for a 1.840" intake valve. Cutting a new 3angle seat for the new valves opens the I.D up considerably. IIRC its in the area of .150". Plus the new valves dont have the over hang margine interfering with piston contact and they are much lighter, not needing a heavier aftermarket valve spring. All that said, a bigger valve is a good move if you are maximizing potential.

With 1 valve relief, .045" felpro crushed head gasket with a bore diameter of 3.600", 3.572" piston, pi head 42cc, you are right under 12.1 static compression. This is all assuming the piston is zero deck and no block decking machine work or no head decking machine work.

Swapping to an aftermarket intake valve will increase chamber cc's as well.

He’s going with 4v heads though.

96blak54 · Feb 16, 2024

And that would make things different!

I assumed it was 2v heads because he stated 2v "fly cuts. I must have missed where he was building with 4v heads. Ive been out of the loop with travel and schooling.