1973 Pontiac Firebird Formula 455-SD

oldskool · 12-17-2021, 05:31 PM

A guy just posted this on a Pontiac forum.

"...Initially NHRA had the SD in G/SA..."

Does anybody here know if this is true ?

If it is, then the H&M T/A may have been running the SD455 engine, when it was marked G/SA.

But, John Clegg won D/S @ Indy '73, in his '73 SD455 Formy. So, if NHRA began the '73 season classing the SD455 T/A in G/SA, looks like they added hp to the SD455, in just a few months.

Can anybody here check this out, to find the exact dates in '73 when NHRA changed the hp factor on the SD455 combos ?

Could they have maybe begun the season using the factory net rating of 290hp, then increased it very early in the season ? Or ?

Would really love to know the exact timeline of all hp factor changes to the SD455 combos, during the '73 season.

I've posted that the H&M '73 T/A was running a D-port 455, when it was classed G/SA. But, it MAY have been SD455 powered, the whole time.

Anybody here know about this ?

oldskool · 12-18-2021, 12:15 AM

Just saw this.

"...In 1972 NHRA came out with a book called the Factor Finder. That book gave all the re-factored horsepowers higher than what the manufacturer listed. Quoting from the Factor Finder book....."The 'factoring' system was developed by NHRA, defining separate performance ratings for use in lieu of manufactures' advertised horsepower listings on many cars in competition". 1972 and 1973 saw the Factor Finder books printed, then followed by putting the refactored horsepower in the Classguide below each engine column. "

So, has anybody here ever seen one of the '72 or '73 "Factor Finder" publications ?

Anybody have one ?

Stan Weiss · 12-18-2021, 12:42 AM

Quote:

Originally Posted by Travis Miller

Refactoring of engine horsepower by NHRA actually started as early as the 60's but it was kept a secret for whatever reason until they published a book called the "Factor Finder" in 1972 followed by an updated version in 1973. Sometime in 1973 is also when NHRA started listing the refactored horsepowers at the bottom of the column in the classguide.

What engine combo are you trying to find out the date when it was refactored?

Stan

oldskool · 12-18-2021, 11:42 AM

There is bound to be somebody here who either has or knows someone who has a copy of one or both these "Factor Finder" publications.

Once again, do you have one or both ?

Do you know anyone who has one or both ?

Does anybody know of an online copy of either year, hopefully a pdf or some version that can be viewed and/or copied or downloaded ?

Gotta be a copy, somewhere. Somebody PLEASE help me locate these "Factor Finder" publications !

12-17-2021, 05:31 PM	#1
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: 1973 Pontiac Firebird Formula 455-SD A guy just posted this on a Pontiac forum. "...Initially NHRA had the SD in G/SA..." Does anybody here know if this is true ? If it is, then the H&M T/A may have been running the SD455 engine, when it was marked G/SA. But, John Clegg won D/S @ Indy '73, in his '73 SD455 Formy. So, if NHRA began the '73 season classing the SD455 T/A in G/SA, looks like they added hp to the SD455, in just a few months. Can anybody here check this out, to find the exact dates in '73 when NHRA changed the hp factor on the SD455 combos ? Could they have maybe begun the season using the factory net rating of 290hp, then increased it very early in the season ? Or ? Would really love to know the exact timeline of all hp factor changes to the SD455 combos, during the '73 season. I've posted that the H&M '73 T/A was running a D-port 455, when it was classed G/SA. But, it MAY have been SD455 powered, the whole time. Anybody here know about this ? Last edited by oldskool; 12-18-2021 at 12:18 AM.

12-18-2021, 12:15 AM	#2
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: 1973 Pontiac Firebird Formula 455-SD Just saw this. "...In 1972 NHRA came out with a book called the Factor Finder. That book gave all the re-factored horsepowers higher than what the manufacturer listed. Quoting from the Factor Finder book....."The 'factoring' system was developed by NHRA, defining separate performance ratings for use in lieu of manufactures' advertised horsepower listings on many cars in competition". 1972 and 1973 saw the Factor Finder books printed, then followed by putting the refactored horsepower in the Classguide below each engine column. " So, has anybody here ever seen one of the '72 or '73 "Factor Finder" publications ? Anybody have one ?

12-18-2021, 11:42 AM	#4
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: 1973 Pontiac Firebird Formula 455-SD There is bound to be somebody here who either has or knows someone who has a copy of one or both these "Factor Finder" publications. Once again, do you have one or both ? Do you know anyone who has one or both ? Does anybody know of an online copy of either year, hopefully a pdf or some version that can be viewed and/or copied or downloaded ? Gotta be a copy, somewhere. Somebody PLEASE help me locate these "Factor Finder" publications !