TRW flat top pistons...
 

Anybody got any idea what compression TRW flat tops will make in a 306? Got a chance to get some in before a dyno run Wednesday.

guessin'
 

thinkin about 10 to 1 ish with TFS out of the box heads, 1.7 RR's and a B303. Anybody? Bueller?

Yep, they'll make it 9.02:1. By the way, I'm dead serious.

Didn't read your signature. TFS heads have a 61cc combustion chamber, that will make your CR 9.43:1.

Oh, here's why.

Stock E7TE. 64cc
TRW Flat top piston with valve relief. Valve relief = 5.5cc.
Total combustion chamber size 64+5.5 = 69.5cc

4.030"x3.00" = 306ci.

Cylinder volume = (pi)(r^2)(h)

pi = 3.14159265359
r = 4.030/2 = 2.015 x 2.54 = 5.1181cm
h = 3.00" x 2.54 = 7.62cm

(3.14159265359)(5.1181^2)(7.62) = 627.08cc

Now take cylinder volume divided by total combustion chamber size.

627.08cc / 69.5cc = 9.02. That's your CR.

If you really want to get technical, stock CR would be 8.89:1

One word...
 

Sweet...

P/N L2488F
 

I'm not sure these have the valve reliefs, trying to find a site with the info. I know I would be right on the limit with a b303 cam as far as lift/duration. But I am looking specifically for compression numbers without valve reliefs.
If that is the case, using your reported numbers and formulas which are accurate, compression would be 10.28 theoretically.
Thanks for a interesting reply.

Deck height?
 

According to Summit, a deck height of 8.2" with a TRW L2488F piston ( yes it has valve reliefs) would yield a compression ratio of 9.98 to 1 with a 61cc TFS cylinder head combustion chamber.
All of this discussion is mainly for blower application consideration and I can have 'em in before my dyno run on Wednesday.

Unit, thanks for the formula! I was wondering what compression ratio I had. This is my exact set up, except I use Windsor Junior heads (58 cc). Thanks again.

Hehe, I could have told you that you already had valve reliefs. It would be like running E7's with a B303 and 1.7's on an 86GT with stock pistons. Mmmmm, valves crunchy.

Sounds like they are a little different than stock replacements. ;)

Ponycar_302, no problem.

Apologize...
 

I apologize for not making it clear Unit about the valve reliefs. I knew there had to be some kind of relief, just not sure what cc effect it had. It is surprisingly difficult to find that kind of detailed information. It didn't even come with the pistons.
Still think my biggest problem is my TFI.
Great exchange of info, I think the cr formula is great. Should be on the tech page.

No need to apologize, just some tech advice flying back and forth across the computer. :)