Mid-Year Dyno Duke-Out - Dyno Might

Find How Much Power Your Corvette Really Has, And Have Fun At The Same Time

Isaac Martin Apr 15, 2008 0 Comment(s)
Corp_0402_01_z Mid_year_dyno_day C2_corvette 1/2

Yes, my engine cranks out 425 hp."

"My Corvette is a numbers-matching LT1, which was rated at 375 horses."

Socializing at a Corvette club meeting, how many times have you heard-or made-statements like that? For decades, Corvette enthusiasts were stuck with factory horsepower figures, making random guesses as to the true power output. But the real key is how much power is actually delivered to the wheels, the true determiner of performance.

Now, with the widespread availability of chassis dynos, you can easily measure your car's power output, and, as we observed, make it an enjoyable gathering for your Corvette club. A dyno event is a perfect excuse to hop into your Corvette and drive to the test location; plus, the testing answers the mystery question: How much rear-wheel power do I really make?

The dyno testing took place at Superior Automotive in Downey, California, using its in-ground Dynojet chassis dyno. Superior's dyno expertise is backed by three decades of performance experience. So, not only can they test, they also have the expertise to execute mechanical work in order to pump up your power numbers.

Enjoy the images of some of the cars that were present, and peruse the dyno results. If your club has a dyno duke-out, by all means go. You may not make the biggest gross score, but you'll enjoy the camaraderie while talking about and enjoying America's premier sports car.

Legend: HP = Rear-Wheel Horsepower
TQ = Rear-Wheel Torque
RPM = Peak Horsepower @ RPM
HP @ Flywhl. = calculated horsepower at flywheel
*Gross Score = total of horsepower (HP) and Torque (TQ)

Like an engine dynamometer, a chassis dynamometer measures rear-wheel torque and horsepower and is calculated by the dyno software. Translating the columns, after displacement comes rear-wheel horsepower (HP) and torque (TQ). The engine horsepower rpm peak is identified in RPM. Finally, the Gross Score is the rear-wheel horsepower and torque added together.

Note that the chart includes a horsepower at the flywheel column (HP @ at Flywhl). The dyno software calculates a default 18 percent power loss from the flywheel through the drivetrain, to the rear wheels. Notice too that the flywheel horsepower ratings don't match any of the factory rating numbers. For example, Brian Pallas' '64 Corvette, with an L76 327, was factory rated at 365 hp. As you will see, the true way to measure drivetrain power loss is to dyno your engine on an engine dyno. Install it in your Corvette, then run it on the chassis dyno. Subtract the numbers, and you've got your drivetrain power-loss percentage.

We thought the horsepower figures noted in our chart would be quite revealing. Like those bench-racing sessions where owners claim 11-second quarter-mile elapsed times, factory horsepower ratings are far from real-world figures. But with a little bit of tuning, those outlandish factory ratings can be achieved and beaten by simple hot rodders' technology. Happy Dyno Day to you.

Legend: HP = Rear-Wheel HorsepowerTQ = Rear-Wheel TorqueRPM = Peak Horsepower @ RPMHP @ Flywhl. = calculated horsepower at flywheel*Gross Score = total of horsepower (HP) and Torque (TQ)

Like an engine dynamometer, a chassis dynamometer measures rear-wheel torque and horsepower and is calculated by the dyno software. Translating the columns, after displacement comes rear-wheel horsepower (HP) and torque (TQ). The engine horsepower rpm peak is identified in RPM. Finally, the Gross Score is the rear-wheel horsepower and torque added together.

Note that the chart includes a horsepower at the flywheel column (HP @ at Flywhl). The dyno software calculates a default 18 percent power loss from the flywheel through the drivetrain, to the rear wheels. Notice too that the flywheel horsepower ratings don't match any of the factory rating numbers. For example, Brian Pallas' '64 Corvette, with an L76 327, was factory rated at 365 hp. As you will see, the true way to measure drivetrain power loss is to dyno your engine on an engine dyno. Install it in your Corvette, then run it on the chassis dyno. Subtract the numbers, and you've got your drivetrain power-loss percentage.

We thought the horsepower figures noted in our chart would be quite revealing. Like those bench-racing sessions where owners claim 11-second quarter-mile elapsed times, factory horsepower ratings are far from real-world figures. But with a little bit of tuning, those outlandish factory ratings can be achieved and beaten by simple hot rodders' technology. Happy Dyno Day to you.

Power: Where Does It Go?Talk about engine power and rear-wheel power, and you're talking about two different things. From the engine flywheel/flexplate, you know the drivetrain will extract a percentage of power loss before it reaches the rear wheels. But the question is, how much?

For some additional insight, we suggest getting a copy of Jeff Smith's cogent article, "The Brutal Truth," in the Nov. '03 Car Craft. In it, the pros at Flowmaster Mufflers dyno'd two engines, installed them in cars, and ran them on Flowmaster's SuperFlow chassis dyno.

One of the test cars was a restored '63 Mercury Comet with a 357ci Windsor with aluminum GT-40 heads, and a 216/220-degree duration (0.050-inch) hydraulic flat-tappet cam. The drivetrain was an AOD and a 9-inch with 3.50:1 gears.

The second car was a '70 Buick GS with a 455 equipped with a 210/218-degree duration (0.050-inch) hydraulic flat-tappet cam. The drivetrain was a Muncie four-speed and a 12-bolt with 2.73 gears.

When the testing was done, the average horsepower loss for the Comet was 36.4 percent! For the manual-equipped Buick, the loss was 18.43 percent. As Jeff wrote, "The biggest culprit in this power-loss chain is the automatic transmission." Remember, a TH400 takes more power to turn than a Powerglide or a TH350 trans.

Surprisingly, one of the biggest power drains was the engine fan. One example was a five-blade, fixed fan on a 380hp small-block. In engine dyno tests, it ate 15 hp at 5,400 rpm. If your Corvette doesn't have to be NCRS judging correct, you might want to consider utilizing a clutch or electric-fan setup instead of a fixed blade.

American Mid-Year SocietyRecently, the American Mid-Year Society (AMYS) Corvette Club held a dyno test event. Founder Brian Pallas purchased his first Corvette, a '64, after his brother got one of the same year. Not unlike other owners, he started fixing and restoring his car and, in turn, meeting Corvette people.

Because of the wide C1 to C5 model diversity, Pallas decided to focus the AMYS on '63-'67 mid-years. Starting two years ago, he attracted members by inviting one owner at a time to join him at a local caf. Pallas told them that they weren't the member, their car was. Word soon spread, and there are currently over 200 cars in AMYS. There are no dues, no meetings (other than regularly scheduled gatherings), and the Corvettes don't have to be NCRS quality. Ultimately, Pallas hopes AMYS will become an international society for mid-years. Future plans include charitable events and an online store to raise funds for philanthropic endeavors.

Sources

Superior Automotive
Anaheim, CA 92801
714-503-1880
www.superiorautomotive.com
American Mid-Year Society
Laguna Beach, CA
(714) 401-5234
www.midyear.org
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