Pontiac firebird replacement engine?

Can a 1970 Pontiac Firebird 400 CI Pontiac engine be replaced with a 1970 544 CI Pontiac engine?

• Answer:

  Everything will mount to the 455 motor.....matter infact, if you use the 400 heads, you will gain some compression in comparison to a like 455 head (ie.. 400 vs 455 6x heads). can I have your old 400 motor? Yes everthing will fit. However, if you are going to drive it on the street you do not want higher compression, the stock compression on most 1970 Pontiac 455s is about 10.25-1 (already too high for 93 octane pump gas). Changing to a 1970 400 head (around 72cc combustion chambers) will put your compression up to about 12.5-1 and require at least 105 octane fuel. If this is for the strip only, or you have a source of affordable race gas then yes higher compression will increase horsepower and torque. On pump gas shoot for about 9.5-1 compression max with iron heads. A great head for a pump gas 455 is the 1971 400 head casting number 96 it has 2.11/1.77 valves and 96cc chambers and will make about 9.5-1 with a stock 455 short block.