Sept. - Oct. 1999 Lane Racing And Rodding Article By Jim Kaekel, Jr.
"I've got over 500 horsepower under the hood!" How many times have we heard someone make that statement?
Just last spring, at a local drag strip, a spectator proclaimed to a racer that his street car was pumping out well over 550 horsepower! He then asked the racer how much horsepower the engine in his race car made. The drag racer replied that it had 483 horses.
Dumfounded, the spectator listened as the racer explained that the number had been obtained by entering his best 1/4 mile e.t. (11.09), miles per hour (118), and the weight of the car with driver (3750) into the horsepower program on his weather station's computer. Perhaps the spectator suddenly began to doubt that he really had 550 horsepower, particularly since it was doubtful his car had taken a single trip down the track, much less run low eleven second elapsed times.
The most accurate method of calculating horsepower is with a dynamometer, but a run or two down a drag strip can provide a fairly accurate indication of approximate horsepower. Feeding factors such as elapsed time, trap speed, car weight, tire diameter, gear ratios, etc. into a computer program such as Mr. Gasket's Desk Top Dyno will yield horsepower numbers that are accurate within +/- 5%.
Moroso likewise offers a Power Speed Calculator (#MOR89650) - a slide rule of sorts - which can also calculate approximate horsepower by using recent e.t. slip information.
In reality, it takes an awfully strong street car engine to top the 500 horsepower mark!
First, we should determine if we're talking GROS horsepower or NET horsepower. Gross horsepower is from the engine alone - less power accessories or drivetrain. Net horsepower, on the other hand, is a "real life" rating with engine accessories in place and drivetrain engaged.
Net horsepower is considerably lower thanks to belt driven accessories like water pumps, power steering pumps, alternators, and so-called parasitic losses caused by transmission drag and clutch or converter slippage. We recall one test of a '66 426 Hemi Dodge, where the gross horsepower was 425 and the rear wheel horsepower was only 318! Quite a drop, but then reality never is as exciting as fantasy.
All of the automobile manufacturers (except VW) played the horsepower game. It was very common for them to manipulate - or "fudge" - horsepower numbers to suit their particular fancies.
Sometimes numbers were inflated to create appeal for a certain engine; while other times, the reverse was true, as "tongue-in-cheek" ratings were applied in order to cushion the effects of the insurance companies outrageously high rates on muscle cars.
Following this line of reasoning, every contender during the Muscle Car era had at least one entry that was factory rated at more than 400 horsepower and a few even claimed as many as 450 horses on tap! Massive cubic inch 454 Chevelles and 440 GTX's ruled the streets, at least until 1970, which was the last year for General Motor's high compression engines.
Ford and Chrysler followed suit after the 1971 model year, and all of a sudden, compression ratios which were commonly in excess of 10.25:1 prior to 1971, were now 8.2:1 to meet increasing federal emission standards and to run on unleaded gasoline with octane numbers as low as 87. Naturally, horsepower ratings took a major hit as a result.
In 1972 the manufacturers changed the horsepower rating system and began rating it in net terms instead of gross. Horsepower no longer was a viable number. A 454 Chevelle was still available, but net rated at only 265 horsepower - ten less than a gross rated 275 horse 327 four years earlier.
Now, let's talk "real world" horsepower. It's not easy to choose the CORRECT parts for a performance street engine. A street engine must be able to idle for long periods of time (without overheating), run both on the highway and on city streets, be relatively quiet (in order to keep the local police happy), and yet have enough "get up and go" to keep its owner happy.
The average hot rodder aims for a sufficient amount of horsepower without unfavorably affecting driveability. Our own Tech Tip: don't shoot for unrealistic horsepower numbers for a "daily driver" just because the numbers sound impressive. Balance towards maximum durability rather than maximum performance. Leave the big CFM double pumper carburetors, solid camshafts and titanium retainers for the drag or circle track racers. Stick with a maintenance-free, reliable hydraulic camshaft. It's possible to build a 500 horse street engine, but be prepared to drop a bankroll and put up with the headaches of running it on the street.
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