Closed chamber heads on a zero decked block

[Omie01]

I had my block zero decked for use with my 76cc chambers. I bought KB flat top pistons w/ single valve relief. How high would the compression be if I installed a set of stock CC heads? Would compression be too high? I do have a bigger cam that I can use, but I'm worried about compression.

 

[MotoArts]

High enough, or borderline, to not be pump gas friendly. Factory guesstimates were 10.7:1 for that combo.

You may be able to modify the ratio slightly with head gasket thickness.

There are online calculators that will let you figure static compression. Google "compression ratio calculator" and experiment with your numbers... http://www.csgnetwork.com/compcalc.html

Cam choice is another can-o-worms that applies to the CR, or vice versa... Do lots of reading, but keep in mind that "the" ultimate cam choice does not exist. (You can drive yourself mental with this subject, so be mindful of your sanity, LOL!)

It all works as a big picture, so to speak.

 

[Don C]

You can calculate the static and dynamic compression ratios with the spreadsheet in this link:

http://www.7173mustangs.com/thread-engine-and-compression-calculations

 

[c9zx]

Assuming 4.030 bore, stock stroke, 5.780 rod, a 4.100 bore gasket that is .041 compressed, true .000 deck, 2cc valve relief, top ring at .275, and a 67cc chamber I get 10.27:1 SCR. With the 76cc chamber I get 9.32:1 SCR.

The dynamic compression ratio depends on when the intake valve closes. Here is some data.

IVC @ 64 degrees ABDC = 8.16 DCR

66 = 8.02

68 = 7.89

70 = 7.76

DCR is not the end all determiner of detonation tolerance but, it is an indicator that is useful. Assuming 91 octane (R+M/2 method), I look for a DCR of 7.8 to 8.0. I am admittedly conservative.

Here is a link to a DCR calculator. http://www.wallaceracing.com/dynamic-cr.php

Other variables such as chamber design, total advance, advance rate, engine temp, and engine load are all players in the detonation game.

Chuck