Compression ratio?

Choosing a cam and need to know my compression ratio.

Decked 383

Decked 452 heads with bowl work

TRW L2293 pistons
(advertised 12.5-1 with closed chamber heads and 11.5-1 with open chamber heads)

Was going to run ported 516s with big valves installed, but was told that I wouldn't have enough piston-to-valve clearance with a big solid roller cam with 600+ lift, so I bought these 452's.

Mark

You’ll need some measurements for us to work with.

head ccs, or at least how much you milled them
Piston top to deck at TDC
bore
Head gasket thickness

PLay around with head gasket thicknesses. They can change the compression ratio a little.

There are several online programs that will do the math for you. You just have to know a few measurements.
http://www.csgnetwork.com/compcalc.html (for example)

Bry

There may be no difference in valve clearance between big valve heads and stock valve heads. It depends completely on the piston valve releifs. That has to be checked.
Cc the heads. It can be done easily. A syringe and a piece of plexiglass is sufficient.

Install a piston and rod and measure how far down it is from the head surface. Assuming the deck is square.
Find the piston dome cc specs...someone on the forum likely has a old book that lists cc for that piston if you don't. It isn't very easy to measure dome cc.
Summits compression calculator is a simple one to use. You can guess and plug in numbers, but the figures are only as good as the input. 452s stock 90cc. 516s maybe 85cc. .070 off is around 74cc for 452. I am not a 516 fan...452s worked over have more potential. 516s have some quench but flow less. Bigger valves is better...usually.

Curiousyellow71 said:

There may be no difference in valve clearance between big valve heads and stock valve heads. It depends completely on the piston valve releifs. That has to be checked.

Click to expand...

This.

I wonder if the recommendation for the 452 over the 516 was due to the possibility of piston to head contact, not piston to valve?

The 452s won't give you any more piston to valve clearance than the 516. And I'm pretty sure you'll have piston to valve clearance issues with any .600 lift cam if the duration is over 250 with the 2293s unless you fly-cut the pistons for deeper valve pockets.

And if we're just spit-balling, you're probably in the 11.0 to 11.5:1 CR. This would assume a clean-up cut on the block and the heads and using a 0.040 head gasket.