I'm rebuilding my TPI 350 and removing my supercharger so I'm looking for some new pistons. The engine is pretty built up - Accel intake/runners/tb, headers, AFR 195 75cc heads, roller cam (not sure on specs)

Using summit's compression calculator I'm coming up with 8.76:1 static compression with +5cc pistons (link below) and .040 head gasket

http://www.summitracing.com/parts/sl...cp30/overview/

Do you think 8.75:1 is too low for daily driver use? I have the 75cc heads because I was running 8.5:1 with the supercharger. If I went with some 0cc pistons I could get the CR up to 9.2:1, but the 5cc pistons are alot less expensive.

 

Check the calculator. Some use a positive value for valve reliefs some use negative. Big difference. Most flat tops with 2 valve reliefs will be 4-7 cc and that would give 10-10.3 to 1 on a 64cc head. Probably a point less on 75cc. For aluminum heads like afr's run as much compression as you can with a matching cam to get the most power. If not after huge power, 9 to 1 is ok with milder cams. Generally 9.5-10.0 is safe on pump gas with most cams, stock to 224 degs duration. Bigger can take more comp

 

Here are the cam specs:

 

.

 

Nice cam for a street 350. Id go 9.5-10.0 comp and it will run hard. Afr 8017 or 8019 springs.

75cc will make it hard to get compression. Likely stick to a flat top and 5cc reliefs and live with it. Not sure id run a dome. Can you shave heads down to 68-70 cc to help?

 

I'm going to be taking the heads in for a valve job. How much do you think I can mill them without having to mill the intake?

 

Probably no more than .030". Thats about 5cc

 

Dave:

What you need is this set of pistons
http://www.summitracing.com/parts/sl...yf30/overview/
They have a dome so you don't need to mill your heads.

They will give you about 10.66 compression, which is just right for a street engine with aluminum heads. (75cc)

I wouldn't mill the heads unless you have to.

We all run 10.4 - 10.8 on our cars.

 

How much HP do you think I'd give up using the 9:1 compression pistons? I'm just a little gun shy after blowing out my rings!

Also, what ring kit goes with those, I think your link was for pistons only.

They also have this hyper piston (a bit cheaper), which would give me 9.9:1, assuming .025 deck, .028 Victor head gasket, 74cc head

http://www.summitracing.com/parts/sl...cp30/overview/

 

I have had problems with hyper pistons so I don't recommend them.
Those have 5/64th rings.
You would give up a lot with only 9.2 and that cam, that is what I calculate.

Forged are sold each.

 

What thickness gasket would you use with that piston (-11cc)? I'm seeing 10.41:1 with a 0.043" and 10.81:1 with a 0.028" gasket.

The other dome piston they have is -2.4cc, which would give me 9.8:1 with a .028" gasket, but it has 5/64" rings.
http://www.summitracing.com/parts/sl...4f30/overview/

Does the ring size make a difference in your opinion?

 

More friction, not desirable for Hi Per

 

Alright Don, one more attempt to stump you:

With the -11cc pistons I'd need to run a thicker gasket (.043) to keep the compression at 10.41, but this would put my quench height at .068".

If I used thinner gaskets (.028) to keep my quench height at .053", my compression gets bumped up to 10.81.

What is the proper way to balance this out? Should I get a piston with a little less dome so I can get closer to .050" quench and maintain 10.5:1 compression?

 

Go with the .028 you won't regret it.
Like I said, we all run 10.5 + and Allen has around 11.0 as do the late model cars being produced today.

 

Go for the quench and don't look back. If you can (feasibly), get a thinner head gasket that puts you closer to .040 quench. I'm running about 11:1 with Dart Iron Eagles, and I took quench over the lower compression from a thicker head gasket. The tighter quench cures detonation better than lowering the compression of just the head gasket thickness.