Quote:
Originally Posted by Jay S
A 455 with 75 cc heads is going to be just over 11:1 with factory type pistons.
|
Since I have done that swap before with 48 heads, (1977) I was fairly certain that the 10.3 number was low. Putting small chamber 400 heads on a 455, and trying to run it on the street with pump gas is going to be a real PITA, IMO.
After trying this combo many years ago when the feds were implementing the unleaded fuel and there was no premium fuel available, only octane booster, I proceeded to blow holes in the pistons of 1, 455, and a 428 with pop up pistons. Upon talking with Nunzi, he told me to look for a set of early 70s 400 heads which relaxed the compression ratio back to a reasonable ratio. I found a set of 96 heads which have advertised 96 CC chamber volume, and could safely run those on a 455 race engine. (69 GP dirt track car in my signature pictures).
From then on, I've tried to keep compression down to keep my 455 and 428 combos happy. The reduction in compression can be made up with port work, and careful cam selection. If you get somewhere that you can't buy good fuel, you can trash the engine quicker than you think. Build for easily available fuel, would be my suggestion. Pontiac was able to pull some pretty good numbers with round port low compression engines, namely the 455 HOs, and the 455 SD combos.
I have run 455 HO heads on the street, and the afore mentioned 96s, as well as a set of 5C heads on a 455 short block. These combos aren't octane sensitive when set up properly, will run on 93 fuel, or less. The 5c heads have a fair amount of port work done, and run quite well in a 76 T/A with 3.23 gears, T400.
Round port aluminum heads would be another choice, they flow better than most ported cast iron heads out of the box, and are more octane tolerant.
