Firebird Transam 455 SD

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

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

sorry i was wrong it is actually between 185 and 210

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.

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.

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

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.

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

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,...

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)

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...

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...

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

in 1963 they made a 421sd that made 410hp

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

Yes, meant '73. Sorry for the fat fingers.
The '71 and '72 HO engines were advertised at 335 horse (gross). The '73 SD was advertised at 310 (net). The '74 SD was advertised at 290 (net).
'69 and '70 Ram Air IV and '70 455 HO were rated at 370 (gross).
Regardless of factory ratings, the 455 SD was the most powerful engine made after '70 (production in ANY American car) until the late '90s. Only now, are we approaching the true power output of that engine, with all the modern technology. SD was a great project. Just wish some had found their way into GTOs and the aftermarket. What a crate motor that thing would be today! A 72 CC version of that cylinder head would sell like there's no tomorrow! The large chamber is the reason it never caught on with the racer crowds. Pontiac engines don't react as well to domed pistons as other engine families.

Yes, meant '73. Sorry for the fat fingers.
The '71 and '72 HO engines were advertised at 335 horse (gross). The '73 SD was advertised at 310 (net). The '74 SD was advertised at 290 (net).
'69 and '70 Ram Air IV and '70 455 HO were rated at 370 (gross).
Regardless of factory ratings, the 455 SD was the most powerful engine made after '70 (production in ANY American car) until the late '90s. Only now, are we approaching the true power output of that engine, with all the modern technology. SD was a great project. Just wish some had found their way into GTOs and the aftermarket. What a crate motor that thing would be today! A 72 CC version of that cylinder head would sell like there's no tomorrow! The large chamber is the reason it never caught on with the racer crowds. Pontiac engines don't react as well to domed pistons as other engine families.


red book differs on your figures, not familiar with the gto engines, and as far as engines are concerned, there is plenty of movement with more and more companies building some great engine castings, for those who have the money.... you can get brand new castings of pontiac engines with improvements over the stock blocks...

1973 S.D. 455 = 310 HP
1974 S.D. 455 = 290 HP

These are net numbers. It was one of the last production 13 second cars until the 1986-1987 Grand National

1973 S.D. 455 = 310 HP
1974 S.D. 455 = 290 HP

These are net numbers. It was one of the last production 13 second cars until the 1986-1987 Grand National


And where did you find those numbers? All my literature is telling me 290!?

And where did you find those numbers? All my literature is telling me 290!?

www.firebirdgallery.com

And

Chilton Auto Manuals

I think I had read it in a High Performance Pontiac magazine a few years back, as well.

www.firebirdgallery.com

And

Chilton Auto Manuals

I think I had read it in a High Performance Pontiac magazine a few years back, as well.


It's getting interesting here. I checked again some of my literature, one Gunnels Firebird Buyers Guide also lists 310 hp, Then "Fabulous Firebirds " also says 310 hp, so I went to the real specialty book, "Pontiac Musclecar Performance 1955-1979" by Pete McCarthy, which has the most comprehensive Engine Codes and part numbers listed, where I now quote, page 51:

"On March 15,1973, the EPA mandated a major change in Pontiacs exhaust emission system. Essentially, the changes involved removal of a solenoid in the EGR system which rendered the EGR system inoperative.as part of the agreement, all engines were recoded according to the chart below, and included all engines after Serial#532727.A casualty of these changes was the 310 HP 455 SD engine (X8,Z8). No 455SD Firebirds were released to the public prior to April, 1973."

INTERESTING isn't it? It basically means that Pontiac had the car advertised with 310 hp, but because of emissions had to cut it back to 290 HP, and therefore never released a 310 HP car to the public!

Yeah it is getting interesting cause some of pontiacs own information clashes with itself.I was just looking and in some cases they even mislabeled the spark sequence.They lied and said 18736542 instead of 18436572.Not only that but ive found head valve and cc contradictions dating so far back that perhaps even later printing modeled after these were incorrect becuse a flaw in the original data.


Also interesting,A few of the 310 hp cars did actually hit the streets because they was already pressed and in shipping and by contract pontiac had to fulfill a few written agreements.Back then high proformance cars were all just about back ordered somtimes years and ive heard a few sources claim because of that fact even more slipped through the cracks only mislabeled.