NHRA Horsepower Ratings for the 273

69 Cuda 440 said

Dart 4 Forte,

If you mill the cylinder heads, and a get to 57.3 CC, and the deck block is
trued, the compression ratio should be in the range of 12.0 to 1.

As for the stock 273/235 HP valve springs, they had a thicker coil than the 273/180 HP 2-barrel engine.

Click to expand...

I just sat down with the guy that builds my motors and using the actual specs of the motor stock from the factory to include the stock steel shim gasket and the domed piston you get a little over 12.2 to 1. The 2 barrel motor using the stock specs the motot CR comes in slightly over 9.2 to 1.

The actual formula can be found in the NHRA rule book.