Compression Ratio for 292


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By idaho211 - 15 Years Ago
I am going to rebuild my 292 in a month and I was wondering what approximate ratio I would be running if:

292 bored .040 over

forged flat top pistons with stock height

G heads ported and polished with high ratio rockers

ford cast 4 barrel intake with mild 4 barrel carburetor

block decked to piston flush

composite gasket possibly fel pro or best gasket

Would I have approximately 9.0:1 ratio?  I have heard not to go over 9.0 :1  if forced to run lower octane fuel. 

Thanks

By 62galxe - 15 Years Ago
should be close. You will need to know the CC of the combustion chambers to calculate the compression ratio accurately.
By mctim64 - 15 Years Ago
Here's two links that might help a little.  Comp. ratios are approx. and depend on what bore and stroke you have but it will give you an idea and let you know what cc the heads are.

http://www.ford-y-block.com/cylinderheadchart.htm   Mummerts site

http://yblockguy.com/yblock_004.htm   My site, I'll admit that John has more complete info than I do. Smile

By idaho211 - 15 Years Ago
Thanks for the information.  Are there some specs to tell if the heads have been shaved which could lower the 69 cc of my G heads?  Thanks again.
By aussiebill - 15 Years Ago
idaho211 (6/7/2010)
Thanks for the information.  Are there some specs to tell if the heads have been shaved which could lower the 69 cc of my G heads?  Thanks again.

A general guide to material removed from head is to measure the square pad thickness on outside edge of the head, it was supposed to be 1.000".

By idaho211 - 15 Years Ago
I measured and they are 15/16 consistently (the height of the square pads on the outside of the head).  Could this be right?  This is .0625 less.  It is an unposted G head.  Is this a workable head?
By Ted - 15 Years Ago
Those measuring pads do need to be measured with a micrometer or at the very least, a dial caliper.  But if your measurement is accurate, then those heads have been milled on the extreme side for what's acceptable for ‘unposted’ heads.  Posted heads can typically take that amount of mill without much issue but unposted heads can have head gasket sealing issues when milled that far and depending upon the final compression ratio.
By idaho211 - 15 Years Ago
I will re-measure but I think they are a done deal.  Well they will make great door stops.