Daniel is correct in that some 272’s did come with factory milled heads which creates some confusion in regards to combustion chamber volumes on those particular heads. One of those head casting numbers were the ECL-B heads where they were factory milled ~0.035” for use on the 1955 182HP Special 272’s versus no milling for the 1955 292 Thunderbird engines. Both engines were rated at 8.5:1 CR.

Lorena, Texas (South of Waco)

I believe some U.S. 272s came with heads that had been milled at the factory, so C/R matched the 292 (?).

6 VOLTS/POS. GRD. NW INDIANA

Simply increasing the engines cubic inch displacement will increase the compression ratio with everything else remaining equal. Something as simple as boring the engine 0.030” over and insuring the piston has the same deck height will increase the compression ratio.

Lorena, Texas (South of Waco)

Jim, The heads are all the same. Check out Mummert's site, I think he has specs for most Ford y heads.

Frank/Rebop

Bristol, In ( by Elkhart) 

Dont forget the 312 has a longer stroke than the 292-272 so you are compressing more air not only in diameter of the cylinder but the stroke also!

55 Vicky & customline

58 Rack Dump, 55 F350 yard truck, 57 F100

59 & 61 P 400's, 58 F100 custom cab, 69 F100, 79 F150, 82 F600 ramp truck, 90 mustang conv 7 up, 94 Mustang, Should I continue?

My apologies if I over-simplified it. It's that whole day-job-gets-in-the-way-of-taking-time-to-formulate-an-intelligent-answer thing.
One thing to take into account when trying to nail the ratio down, as mentioned before, is head gasket volume. Were they doing the original calculations with a specific head gasket in mind? If so, did they match head gasket opening to cylinder diameter or to a universal-fit gasket? In other words, a head gasket that just fits a 292 or 312 would cause a greater minimum chamber volume on a 272 due to its diameter being much greater than the cylinder diameter. It never fails, I need to go to my day job so I don't have time to poke some figures into a spreadsheet.

OK, I took the time to poke numbers into a spreadsheet and, using 73cc for chamber volume on the heads and a 0.04" head gasket thickness, I came up with the following (assuming head gaskets meet bore diameter, which is an unwise assumption):
272 = 7.97/1
292 = 8.44/1
312 = 8.94/1

That's close enough for government work.


BTW: another pair of unsafe assumptions were used to get those numbers. Those are a deck height of zero and a piston top volume of zero.

A side note on all these cylinder volume calculations. According to John Mummert, most of Fords advertised compression ratios on Y-Blks were optimistic by about 9 percent. As for ECZ-C heads, Mummert says the main performance limitation with them is that the lower port will not flow as good as the upper, even with a good porting job. However, they are not prone to combustion chamber failures like sometimes occurs with early "G" heads, particularly if they are milled very much.

Paul

Actually, I used the whole engine displacement. Divide by 8 for one cylinder. So for an engine displacing 272 cubic inches, whole engine combustion chamber volume (at 8.0:1 compression) works out to 38.86 cubic inches. Thats 4.86 cubic inches per cylinder. Or 79.6 cubic centimeters.

If you know the displacement (difference between total volume at BDC minus total volume at TDC), and if you know the compression ratio, then you can calculate the combustion chamber volume (aka volume at TDC). You don't know how much of that is attributable to cylinder head volume or gasket thickness or how far above or below the top of the block the piston travels.

In practice, you are calculating compression ratio and all the other bits are known or need to be determined. So this calculation may seem weird. But I think it is correct.

And the original question was - is there a difference between heads on the different engines. The calculations show different combustion chamber volumes, so it seems that yes, there was a difference. Beyond the calculations, I too am interested in if there really was a difference in heads or not. And why the numbers work out as they do.

Jim - Erie Colorado, 1957 Country Sedan

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

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.