How are the compression ratios arrived at with these heads? On J Mummert's site, the 272 2bbl has a ratio of 8:1, the 292 4bbl has 8.4:1 and the 312 has 9:1.


South Australia

It's (theoretically) the ratio of max chamber volume to min chamber volume.
So, assuming that the max chamber volume changes by a significant percentage and min is very close to the same value, compression ratio will increase. Thus the differences.

ECZ-C's are good for turbo engines. We went 8.885 on a quartermile this summer with set of those heads. Not bad for a heads that everybody says not to use in performance engines and lot's of compression or boost .

http://www.youtube.com/watch?v=8_jATbrygbU

 Seppo from Järvenpää, Finland
www.hollowheads.net (just click the hole in the head to proceed)

Keeping it simple, compression is (Cylinder Volume + Combustion Chamber Volume) / Combustion Chamber Volume

There are different heads with different sized combustion chambers. With the same displacement, a larger chamber decreases compression. A smaller chamber increases compression. Or with the same heads, a smaller cylinder decreases compression and a larger cylinder increases compression.


Lawrenceville, GA

HUH???

charliemccraney (8/26/2013)

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Keeping it simple, compression is (Cylinder Volume + Combustion Chamber Volume) / Combustion Chamber Volume

Hence, with the larger Cylinder Volume with the larger engine with the combustion chamber staying the same size, the compression ratio increases.

"The Master Cylinder"

Enjoying life at the beach in SOCAL

If we start with



and then plug into the formula (displacement + combustion chamber volume) / combustion chamber volume = compression, we get


(272 + X) / X = 8 or a combustion chamber volume of 38.86. The 292 would be 39.46. The 312 would be 38.52.


So math says something must be different. If I didn't mess up. Or it could be that "272" etc. is not accurate enough to use in this calculation...

Jim - Erie Colorado, 1957 Country Sedan

You're getting there, You'd also need the volume of the head gasket. your result is then divided by the amount of the chamber, gasket, deck volume and whatever valve cutouts or dishes are in the piston.

In other words you divide the total amount of volume at top dead center into the total volume at bottom dead center. Clear as mud?

Frank/Rebop

Bristol, In ( by Elkhart) 

Yuummm, Ima thinkin' it's not an exact science? More like a ballpark figure??

"The Master Cylinder"

Enjoying life at the beach in SOCAL

Of course Cyl head volume is usually expressed in cc which stands for Cubic Centimeters. The engine displacement is expressed in cubic inches 1 cubic inch is 16.39 cc's. the usual volume of Y cyl heads is ~ 75 cc's which is 4.57 cubic inches. The units must be consistant for the formulas to work.

Or you could just buy my set of G heads

Doug T

The Highlands, Louisville, Ky.

Jim, I just reread your post. You have to use the displacement of one cylinder in the formula, not all eight.

And yes Doug. Good point. You have to be consistent with the units of measure.

"The Master Cylinder"

Enjoying life at the beach in SOCAL