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Old horsepower vs New horsepower rating?

12K views 9 replies 8 participants last post by  -SS454- 
#1 ·
Was watching American Muscle Car this morning and they mentioned how the 426 Cuda was rated at 425 hp while it really was more like 500 hp.

The 396 was traditional a 325/350/375 horse deal. What was there acutual horsepower?

How does this relate to the 454 crate motors now that say 425 horses or the zz4 which proclaims 355 horses?

What is the major difference in determining horsepower.
 
#2 ·
Aaron said:
The 396 was traditional a 325/350/375 horse deal. What was there acutual horsepower?

How does this relate to the 454 crate motors now that say 425 horses or the zz4 which proclaims 355 horses?

What is the major difference in determining horsepower.
Would also like to know......
 
#3 ·
My take on it the Hemi may have been rated at lower than its peak power to get a softer class in the NHRA, or to fool the insurance companies, or that 500 hp is bullstuff and it really did only make 425 hp. Most stock hemis only ran low 13s anyway.

I do understand that between 1971 and 72 they changed from "gross" to "net" horsepower. My understanding is that gross may have been with headers and no accessories (water pump, alternator, fan) and net was with all the engine driven accessories in place and stock exhaust manifolds. Bottom line that with no changes to the engine itself power ratings dropped about 80 hp. More for some engines less for others.

Not sure how the current crate engines are rated, but a fellow TCer was running bottom 12s with a stock ZZ-454 in a 67 last fall. So I'd be inclined to believe that it was making at least the advertised 440 hp. My 72 with a stock ZZ 502 ran low 12s and I believe it long overdue for a tune. So I think the 502 hp claim is at least legit.

Oh and if you look up the spec.s the same 375 hp 396 in a Chevelle was rated at 425 in a Corvette with the only difference being the exhaust manifolds. Line up a 375 hp 396 and a 350 hp 396 and I'd bet the difference at the finish line indicates more than a 25 hp difference.
 
#4 ·
There was a big thing with the insurance companies that if you made more than 1 hp per cubic inch, the costs went up. Which is why you often see power figures that are very close to the cubic inches, but not over.

Another huge difference is gross and net horsepower, net being power with accessories. I think one of the biggest factors, is its just a number rating. Numbers sell.

Despite the belief that the old engines were all these drastically underrated, super monsterous 600 hp engines, they often not nearly as powerful as people believe. Like the Hemi being 500 hp, well I seen a factory dyno sheet on the 426 Hemi, and it made 433 hp, and I think 466 ft-lbs, and I think that was with headers. ZL1 427, ppl think its 600 hp, stock it didnt even come up to 500 hp, after headers (no exhaust), and tuning and stuff, it made 523 hp. 100% bone stock when you put it in the real world, the factory ratings quite a bit off, and they dont make the power as one would expect due to the SAE net standards.
 
#5 ·
Ahh yes, another one of those urban musclecar legends that will not die - but it does sound good!

One thing that is well known is that the "Gross Horsepower" ratings of engines back then was fairly bogus. Maybe the street hemi was less bogus than some others, but word on the street was that the hemi could be beat by all manner of lesser motored musclecars. The hemi certainly had a lot of potential, but in as delivered form the actual performance did not measure up to those 500 horsepower claims.

Thomas
 
#6 ·
I just got through reading in the Auto Math book by John Lawlor the Hemi was underated but only because they didn't do the math for Horsepower above 5000 rpm when that engine clearly still made torque above that rpm. He showed that the true Hp peak is 6000 and there using Chrysler torque numbers it made 470 hp @ 6000. By the way most all the manufactures did this at one time or another, it is just that most want to believe the numbers are way higher than they really were. The Hemi with headers and a good tune probably did make the magic 500 or damn close, just like the ZL-1 and the LS-6. I mean come on does anyone really believe that the differnet 455's from all the other GM guys only made 350 to 370 hp when they made 500 to 510 lbft of torque, these engines were more likely in the 390 to 420 range.
 
G
#7 · (Edited)
I have a REALLY old mag somewhere that gathered up all this info and they came to the conclusion that a 375&425hp/396 was actually right at 410hp.

As for the bad-boy motors, it was where they ran the numbers. Like the 12.5 to 1 CR. L-88 was only 430hp vs the 11 to 1 CR. tri-power equipped, 435hp/427.

They dropped back on the rpm to pull this one off is all.

And one way under-rated motor was the Ford 428 CJ at 335hp or some such low hp number!!

I think the article said that Olds did get their "W" motors about right-on if I recall right for back then...

pdq67

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#8 ·
pdq67 said:
...As for the bad-boy motors, it was where they ran the numbers. Like the 12.5 to 1 CR. L-88 was only 430hp vs the 11 to 1 CR. trip 425hp/427.

They dropped back on the rpm to pull this one off is all...pdq67
I'd read in one of my Vette history books that the L88 was deliberately advertised at 430 to discourage street driving yokels from buying it...the pitch would go something like, "It's only 430 HP you have to use racing gas and it's only got one 4bbl carburetor. You can buy this 435 horse TRIPOWER 427 for much less, use just premium fuel and have 5 horses more for less money, and less hassle! And look how good that triangle shaped aircleaner looks. C'mon, more horses, less money you want the tripower right?" Real gearheads knew the difference but your average car nut would look at the numbers scratch their head and buy the tripower. Chevy only wanted REAL racers to buy the engine so they wouldn't have the service/warranty problems they knew a street driven L88 would give them.
 
#9 ·
I was always led to believe that the early horsepower ratings were at the crank, while '71 and later ratings were from the rear wheels. Makes sense to me when defined as "gross" and "net".
 
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