Compression Ratios


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By Ted - 14 Years Ago
Paul.  Your question is a good start for a new thread.

PF Arcand (6/30/2010)
John: Possibly this has been covered before but I've not seen it. If your new heads are installed on a 292 or 312 with stock pistons (lets assume the block is not over bored more than 0.020 thousands) in a non decked block, what will the approximate compression ratios be? Thanks.

9.09:1 static compression ratio for a 292 with 0.020” overbore and pistons in the hole 0.025” with the Mummert aluminum heads (60cc).  G heads at 69cc’s on the same engine will have a cr of 8.22:1 while the 113 heads at 72cc’s will lower the cr even more to 7.97:1.

 

9.65:1 static compression ratio for a 312 with 0.020” overbore and pistons in the hole 0.025” with the Mummert aluminum heads (60cc).  G heads at 69cc’s on the same engine will have a cr of 8.72:1 while the 113 heads at 72cc’s will lower the cr even more to 8.45:1.

By aussiebill - 14 Years Ago
Ted (7/4/2010)
Paul.  Your question is a good start for a new thread.

PF Arcand (6/30/2010)
John: Possibly this has been covered before but I've not seen it. If your new heads are installed on a 292 or 312 with stock pistons (lets assume the block is not over bored more than 0.020 thousands) in a non decked block, what will the approximate compression ratios be? Thanks.

9.09:1 static compression ratio for a 292 with 0.020” overbore and pistons in the hole 0.025” with the Mummert aluminum heads (60cc).  G heads at 69cc’s on the same engine will have a cr of 8.22:1 while the 113 heads at 72cc’s will lower the cr even more to 7.97:1.

 

9.65:1 static compression ratio for a 312 with 0.020” overbore and pistons in the hole 0.025” with the Mummert aluminum heads (60cc).  G heads at 69cc’s on the same engine will have a cr of 8.72:1 while the 113 heads at 72cc’s will lower the cr even more to 8.45:1.

 

Ted or perhaps John M, i cant recall any mention on the new aluminum heads if they are posted in some way  or cast with reinforcment to prevent problems encountered with CI heads, and what torque tension would apply to these heads using ARP screw in head studs. thank you, regards bill.

By Ted - 14 Years Ago

For the first round of testing on the aluminum heads, ARP 7/16” bolts were used.  The long bolts (top row) were torqued to 75 lb/ft while the short bolts were torqued to 70 lb/ft.  Upon removing the aluminum heads from the engine after 78+ dyno pulls, the head gaskets showed zero issues.  No distress at all.

By John Mummert - 14 Years Ago
Bill. the factory heads needed a post due to extremely thin decks. Near the coolant passages they are approx .280" thick. Even over the cylinders they are very thin.

The new heads are .600"+ and since there is more material around the ports the deck surface of the head spans a shorter distance.

By aussiebill - 14 Years Ago
John Mummert (7/5/2010)
Bill. the factory heads needed a post due to extremely thin decks. Near the coolant passages they are approx .280" thick. Even over the cylinders they are very thin.

The new heads are .600"+ and since there is more material around the ports the deck surface of the head spans a shorter distance.

John, thanks for that, i thought along those lines but was curious, good job.Tongue