Firebird Transam 455 SD

[cooltc2004]

What exactly is the horsepower to this car? Pontiac never really advertised it. I do believe that it was in 1973, right?

[custom mccannix]

i believe that it was around 220-250 but not sure and if it was an a/c motor made it different. i will look up the numbers

[custom mccannix]

sorry i was wrong it is actually between 185 and 210

[cooltc2004]

If its that low, then how was it the most powerful engine of the year. With all the economy bs all engines dropped compression ratio etc etc etc, and the pontiac 455 SD became one of the fastest cars of the years to come. I cant see it being THAT low.

[volkerc]

Originally Posted by custom mccannix

sorry i was wrong it is actually between 185 and 210

Nonsense,
a 1973 SD with engine codes ZJ and XD are rated at 290 hp, one code designates the auto and the other the manual transmission.regular 455's were rated at 250 hp that year.In 1975 and 1976 the power went down to 200hp because of emissions.

Now I know they changed the way horsepower was calculated, but I'm not sure when that was, probably before 73.In 1971 the first year for the 455 in firebirds the rating was 335 hp.
Hope that helped you.

[custom mccannix]

they changed from what they call Brake Horsepower(bhp) to using a no load (hp) in the late 70's because of emissions it did not sound good when the bhp of an engine was only 90bhpwhen you could just say that it was 210hp. the difference was bhp dynos simulated all the accessories and the rest of the car. the hp dynos of today only simulate atmospheric pressure which is no load at all. i may be wrong on that particular engine but is was figuring bhp with a 3850lb car, no a/c, 185lb driver,which gave me that estimate,but that would be around 300-320hp in our dyno world today

[volkerc]

Originally Posted by custom mccannix

they changed from what they call Brake Horsepower(bhp) to using a no load (hp) in the late 70's because of emissions it did not sound good when the bhp of an engine was only 90bhpwhen you could just say that it was 210hp. the difference was bhp dynos simulated all the accessories and the rest of the car. the hp dynos of today only simulate atmospheric pressure which is no load at all. i may be wrong on that particular engine but is was figuring bhp with a 3850lb car, no a/c, 185lb driver,which gave me that estimate,but that would be around 300-320hp in our dyno world today

getting technical now. The numbers I quoted are official Pontiac numbers for those days. Now if you are saying that they changed from bhp to hp in the late 70, that would mean that the 290 hp rating for the '73 SD 455 was in bhp, than hp with no accesories would have to be even higher!! Either way, 290 horse is the correct number according to POntiac, be it bhp or hp needs to be figured out.

[custom mccannix]

that would be what i am saying and it would be great to find out if it is bhp or hp

[volkerc]

Originally Posted by custom mccannix

that would be what i am saying and it would be great to find out if it is bhp or hp

to be honest, i'm thinking it is the other way around,...

[MrPbody]

Actually, the '83 was rated at 310 Net HP and the '74 was the 290 version. According to some Pontiac afficianados, the change was due to the exhaust system not being as "free flowing" on the '74.
The rating system was changed from '70 to '71. It went from "gross brake horsepower" (at the flywheel, dyno load only) to "SAE Net horsepower" (measured at the tailshaft of the transmission with accessories installed and operating). Some '71s appear to have GBH ratings, and others have the "Net" ratings.
455SD was the most powerful engine Pontiac had built up to that time, for a street production car. Considering the low compression ratio (8:1), that's saying a lot. A piston and cam change made for "instant" 500 horsepower... (GBH)

[volkerc]

Originally Posted by MrPbody

Actually, the '83 was rated at 310 Net HP and the '74 was the 290 version. According to some Pontiac afficianados, the change was due to the exhaust system not being as "free flowing" on the '74.
The rating system was changed from '70 to '71. It went from "gross brake horsepower" (at the flywheel, dyno load only) to "SAE Net horsepower" (measured at the tailshaft of the transmission with accessories installed and operating). Some '71s appear to have GBH ratings, and others have the "Net" ratings.
455SD was the most powerful engine Pontiac had built up to that time, for a street production car. Considering the low compression ratio (8:1), that's saying a lot. A piston and cam change made for "instant" 500 horsepower... (GBH)

That's what I thought about the change in hp rating.
But when it comes to your quote about the hp versions, I stick with official books, like the red book and official Pontiac material. Where the rating for the 72 455 is 300 hp, 290 hp for the 455 SD, 290 for the 74 SD455.And I'm sure you meant '73 and not "83 in your answer...

[volkerc]

Originally Posted by MrPbody

Actually, the '83 was rated at 310 Net HP and the '74 was the 290 version. According to some Pontiac afficianados, the change was due to the exhaust system not being as "free flowing" on the '74.
The rating system was changed from '70 to '71. It went from "gross brake horsepower" (at the flywheel, dyno load only) to "SAE Net horsepower" (measured at the tailshaft of the transmission with accessories installed and operating). Some '71s appear to have GBH ratings, and others have the "Net" ratings.
455SD was the most powerful engine Pontiac had built up to that time, for a street production car. Considering the low compression ratio (8:1), that's saying a lot. A piston and cam change made for "instant" 500 horsepower... (GBH)

Have to disagree with you on :"455SD was the most powerful engine Pontiac had built up to that time, for a street production car"

The most powerful engine was the 1970 400ci 370 hp Ram Air IV found in the T/A's. The 455 was the biggest cubic inch wise, and remained in their performance cars, long after Chevy and Ford had already pulled their big engines out of their performance cars...

[hotrod_chevyz]

WTF a super duty 455 had 290hp.and pontiac made a 410hp engine so>

[hotrod_chevyz]

in 1963 they made a 421sd that made 410hp

[hotrod_chevyz]

here take a look http://www.bassettracing.cz28.com/custom3.html