Car Corner
Muscle Car Horsepower

February 1, 2008
By Scott Lewis

I saw an episode of American Muscle Car where they put a series of engines on a dynamometer to determine the real horsepower of 5 legendary Muscle Car engines.

I am pretty sure one of the engines was smoke dope, or the dyno operator was. But we will get to that in a minute.

The premise of the show was to determine how much horsepower these engines really made. In the day the manufacturers lied a lot about horsepower. There were to main reasons to lie. 1) Insurance rated were climbing sky high and the insurance industry went by the horsepower rating to help them price out insurance. A car with 290 hp was going to be easier to insure than the same car with a 400 hp engine. 2) Racing. Cars and their engines were put into classes in racing, mostly drag racing. A car with a factory rating of 335 hp would be put into a lower class. The fact that the car really had over 400 hp helped it win racing in this lower class.

So, how much did they lie back then. Well, it is hard to say. I remember hearing that one trick for lieing was to just use the horsepower at a different RPM. Let's say you have an engine with a horsepower rating of 450 hp @ 6200 RPM. YOU take the horsepower rating at 5000 RPM, a conservative 360 hp. Genius!

AMC showed 5 engines that were rebuilt to exact factory specs. These were restoration rebuilds, where factory spec or "blueprint" parts were used. So what engines, and what were their real horsepower.

Engine Factory Rating AMC Dyno Results
Chevrolet "Fine" 409 409 hp 406 hp
Ford 427 "Hi-Riser" 425 hp 637 hp
Pontiac 421 Super Duty 405 hp 488 hp
Chrysler 426 Hemi 425 hp 820 hp
Chevrolet L88 427 425 hp 527 hp

Let's take a look at these numbers. She's So Fine, My 4-0-9. I was not too surprised that 409 came very close to it original horsepower rating. This engine came out before the insurance problems of the times and Chevrolet may or may not have been directly involved in racing at the time.

I was a little surprised about the Ford 427. I don't remember exactly what they said on the show, but they mentioned something about using a medium riser manifold because that's what they had available. I would not have guessed over 600 horsepower, but I supposed it is possible. I would have guessed 525-550.

Next up the Pontiac SD 421. For those of you that don't remember, Car and Driver did an article in 1964 comparing a Pontiac GTO to a Ferrari GTO. The problem with that article was two-fold. First, they didn't actually have a Ferrari to do the comparison. They used previous test data on the Italian Goat to compare against the American car. That wouldn't be bad enough, except the car Pontiac supplied to Car and Driver had... you guessed it... a SD 421 engine instead of the 348 engine it was supposed to have. So, the SD 421 was also underrated. This is not surprising as Pontiac ruled the drag strips with the Super Duty cars.

Let's go out of order for a moment and cover the L-88 Corvette. The L-88 is quite rare. Vettes with this engine will fetch six figures. In the day this engine was geared toward stock car drag racing. Chevrolet didn't want regular people buying it. They wanted racers buying it. So, they rated it at 425 hp. Racers knew this was bogus. At the time, they hoped to fool the regular guy that went into a dealer and checked the option box next to the highest horsepower. The highest horsepower engine was a 427 with 3 - 2 barrel carbs rated at 435 hp. Racers knew the L-88 was good for over 500 hp. And we hit that well here. This one seems right on to me.

Finally we come to the legendary Hemi. No. That was not a typo. The engine they ran generated 820 horsepower, and it did it at 6400 RPM. Now, I know a little about engines, and I can tell you for a fact... an engine is not going to make 2 hp per cubic inch at only 6400 RMPs without some kind of force induction. You need air and fuel in the combustion camber to make power. A normally aspirated engine, even at 100% volumetric efficiency is not going to make this much power unless you rev it out to something like 8000-9000 RPM.

What's worse is that why would anyone buy a 526 cubic inch crate Hemi rated... accurately... at 610 hp when if you could build a stock 426 hemi and get over 800 horsepower. Look at it this way... if the 426 Hemi really was make over 800 horsepower in the day why weren't Hemi powered cars racking up significantly faster times in road tests that 454 powered Chevelles or L-88 powered Corvettes.

Either the dyno operator or the engine were smoking dope. The 426 Hemi never made 820 horsepower is stock trim. Period!


Well, except for the bogus numbers on the 426 Hemi this was a very informative show. However, I would have liked to see a handful of other engines. Let's see, here are 5 more engines I would have liked to see put on a dyno for an accurate reading:

Chevrolet 302 Z-28 - This engine was rated at 290 hp. People think it was actually closer to 400 hp. It certainly could rev, and I would love to know what it really was capable of.

Ford Boss 302 - This would be the ultimate dyno shootout, the 302 Z/28 engine versus the Boss 302. Of course Ford rated this engine at... yep, 290 hp. With intake valves in those Cleveland cylinder heads the same size as a big block Chevy, this engine shoud be able to out breath the Chevy small block. But could the engine hold itself together long enough to generate a high rating. Hmmm.

Chevrolet LS-6 454 - This engine was rated at 450 hp, the highest horsepower rating of any Muscle Car engine from the era. How much power did it really make? I owuld like to know.

Buick 455 Stage I - This is the torque champ. Rated at 510 ft/lbs of torque it was rated the highest rated torque rating of any engine at the time. But it was only rated at 360 horsepower. Stage I Buicks ran right there with Hemi and LS-6 powered cars. How much power did it really have?

Chrysler 426 Hemi - Yea, they already did it. But they botched it up so badly that I want to know what a real 426 Hemi would put out.