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Project Corvette Dyno Results Are In!

By April 29, 2010

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As I mentioned this morning, I took the project Corvette to Modern Classics in Lake Oswego, Oregon for some evaluation and tuning today. It was well worth the price, as I learned a lot of useful things about this car in particular and Corvettes in general.

"This car needs help," said Steve Heino, owner of Modern Classics. Among the many things Steve noticed that need to be fixed, Steve noted that the vacuum booster for the brakes was not holding vacuum, and he pointed out that because of the Chevrolet intake manifold design, this would cause a lean mixture condition in one of the cylinders - effectively preventing that cylinder from firing! So as our first order of business, we replaced the vacuum boost module with a working unit.

We also ran the Corvette on the shop's chassis dynamometer. This is a device that is built into the floor of the shop, and includes a large roller that comes up under the car's rear tires. The mechanics strap the car to mounting points for safety and then "drive" the car with the rear wheels on the roller. The machinery in the floor calculates the horsepower and torque that the car is actually delivering to the wheels. These figures are almost always lower than claimed horsepower and torque numbers because of friction losses in the car's drivetrain.

This L-48 base engine Corvette was estimated at 180 horsepower the day it rolled off the production line in April of 1977. Over the years, that horsepower number can be expected to drop quite a bit, so I was pleased to see that Steve's dyno reported that even in its sorry state of tune, this Corvette delivered 137 peak horsepower to the wheels. What was better, the engine was putting out a muscular 216 pound-feet of torque. We'll improve those numbers over time, but on a 33 year old car, that's quite respectable.

Replacing the vacuum booster helped smooth out the engine's burbles and shakes, but Steve pointed out that the entire ignition system needs freshening before we can get started tuning the carburetor. So I've ordered a complete ignition kit (costing about $200 for plugs, plug wires, distributor cap and rotor, and a high-output ignition coil) for the car, and I'll post an article on how to install those parts before we take the car back to Steve for carburetor tuning.

The best news is that we're close to passing the strict Oregon emissions test that's coming up for this car in June. With the ignition system freshened and the carb tuned, I think we'll be in good shape. And in the meantime, the car's more fun to drive than it was this morning!

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