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oldskool · 09-08-2021, 02:35 PM

"1974 455 rated at 310 hp with 102cc combustion chamber.

1975 and 1976 455 rated at 300 hp in SS with 120 cc chamber..."

My guess is that the difference in compression would be worth more than the 10hp difference NHRA allows.

Only advantage I can see to the later models is the 800 cfm Q-jet. But, since the 750 Q-jets are running low 9's & even high 8's, on 428 GT cars, I don't figure the extra 50cfm of carb will make up for the loss of power from the compression difference.

But everybody knows I'm no expert. Does anybody here have the knowledge to accurately figure the power potential difference in these 2 engines ?

I've never read of or heard of anybody running the '75-'76 455 in any Stock/SS car. I'm guessing that the huge chamber volume, together with the 310/300hp numbers, is the reason why.

With that big chamber, I'd think NHRA would have to lower the hp numbers considerably, in order to make those engines competitive.

Considering the chamber size reduction NHRA allows for many other Pontiac engines, that 121.51 number is NOT very generous. Most sources list the factory chmaber size to be only about 124cc. So, NHRA is allowing only a VERY small reduction.

IMO, NHRA should either allow smaller chambers or reduce the hp factor. Unless they do one or the other, it's not likely anybody would ever choose to run this engine in either Stock or SS. But, the chances of getting NHRA to to that are probably slim to none.

However, somebody got an aluminum round port head OK'd for use on a 428 Pontiac engine, which came only with D-port heads. So, miracles do happen.

Don't think too many people ran a 428, before that. Since then, there have been lots of GT cars run a 428, including Chevy bodied cars.

If the 87cc Edelbrock alum heads were allowed on a 455, & NHRA gave it a decent hp factor, there would probably be quite a few guys try one. Since the old iron is getting really old now, and since so many aftermarket heads are now legal for Chevy stuff, I don't see why NHRA shouldn't allow alum heads for more Pontiac engines. Hey, there has been nothing "Stock" about many Stock/SS engines, for a long time. So, what difference would it make to allow alum heads on a Pontiac engine ? If they made too much power, for the NHRA hp factor, I'm sure the Chevy guys would raise enuff cane to get NHRA to fix it.

09-08-2021, 02:35 PM	#66
oldskool VIP Member Join Date: Dec 2014 Location: The Land of Bayous, Boudin & Crawfish Posts: 1,668 Likes: 223 Liked 747 Times in 362 Posts	Re: Pontiacs "1974 455 rated at 310 hp with 102cc combustion chamber. 1975 and 1976 455 rated at 300 hp in SS with 120 cc chamber..." My guess is that the difference in compression would be worth more than the 10hp difference NHRA allows. Only advantage I can see to the later models is the 800 cfm Q-jet. But, since the 750 Q-jets are running low 9's & even high 8's, on 428 GT cars, I don't figure the extra 50cfm of carb will make up for the loss of power from the compression difference. But everybody knows I'm no expert. Does anybody here have the knowledge to accurately figure the power potential difference in these 2 engines ? I've never read of or heard of anybody running the '75-'76 455 in any Stock/SS car. I'm guessing that the huge chamber volume, together with the 310/300hp numbers, is the reason why. With that big chamber, I'd think NHRA would have to lower the hp numbers considerably, in order to make those engines competitive. Considering the chamber size reduction NHRA allows for many other Pontiac engines, that 121.51 number is NOT very generous. Most sources list the factory chmaber size to be only about 124cc. So, NHRA is allowing only a VERY small reduction. IMO, NHRA should either allow smaller chambers or reduce the hp factor. Unless they do one or the other, it's not likely anybody would ever choose to run this engine in either Stock or SS. But, the chances of getting NHRA to to that are probably slim to none. However, somebody got an aluminum round port head OK'd for use on a 428 Pontiac engine, which came only with D-port heads. So, miracles do happen. Don't think too many people ran a 428, before that. Since then, there have been lots of GT cars run a 428, including Chevy bodied cars. If the 87cc Edelbrock alum heads were allowed on a 455, & NHRA gave it a decent hp factor, there would probably be quite a few guys try one. Since the old iron is getting really old now, and since so many aftermarket heads are now legal for Chevy stuff, I don't see why NHRA shouldn't allow alum heads for more Pontiac engines. Hey, there has been nothing "Stock" about many Stock/SS engines, for a long time. So, what difference would it make to allow alum heads on a Pontiac engine ? If they made too much power, for the NHRA hp factor, I'm sure the Chevy guys would raise enuff cane to get NHRA to fix it.