The Greenwood C4s

by Mike Guyette

Just as the third generation Corvette left room for improvement, so did the fourth, also known as the C4 Corvettes. Production years ran from 1984 until 1996 and a slew of Corvette tuners jumped on the aftermarket bandwagon.

The Greenwoods were no different in that respect, but much different in many other ways. With years of racing experience in machines that would handle more than 700 horsepower and untold g-forces, Burt and John found that in order to make the perfect street car they had to basically start with a clean sheet of paper.

As their C3 street cars evolved from their race cars, which were initially based on production Corvettes, so too did the evolution of the C4 program. Their first foray into the world of the C4 brought about suspension, aerodynamic and sound dampening improvements. With the demise of the Corvette convertible in 1975, the Greenwoods decided it was time to resurrect the topless American sports car by fabricating their own convertible conversions.

As they focused on one particular aspect of improving the C4 and successfully achieving superior results, they found that other areas of the Corvette were adversely affected. As one area was perfected another became lacking in the quality for which the Greenwood brothers had become famous. Many years of research and development went into the defining of the perfect “entertainment system”.

Not unlike their C3 products program, the Greenwoods offered to the public various body kits, suspensions mods, and aftermarket wheels and stereo systems. As their penchant for perfection consumed them, they found that ultimately the C4 Corvette would have to be stripped down to the bare chassis and be rebuilt from the ground up using heavier duty components for most of the suspension and braking systems. Sound deadening and insulation, along with some custom fabricated trim pieces, were crucial in achieving a truly rattle-free environment. Chassis strengthening became necessary to handle the torque and cornering forces predicted from the eventual big block models that one day would be. Years of experience in tubeframe construction were incorporated into the chassis design, one rigid enough to surpass even the capabilities of GM’s own C5 Corvette.

Many Corvette tuners of the time would offer a supercharger here and some shocks-and-swaybars there, but few had the experience, or patience, to offer a complete package that was in effect, a completely different car. Although the Greenwood series of C4 Corvettes - the G-350, G-383, and unrealized G-572 - had some visual semblance to the stock Corvette, that is where the comparison stopped.

John and Burt spent several years fixing the flaws inherent to the C4 chassis and then bringing the G-350 and G-383 to market. Despite the high cost of re-engineering the C4 chassis, a few of John's stupefying G-350 and G-383 Corvettes were sold. But not enough to reap a payback. John came to the conclusion that there was still more work to be done to reconfigure his latest creations to be able to offer them at a reasonable price. The Greenwood brothers once again buried themselves in new research. And now, they're back.

Sidebar by John Greenwood

The G-Series C4 program has proven quite difficult. When the C4 Corvette was redesigned, it had tremendous promise. If it could have lived up to its promise there was no way the Viper could have ever beaten a ZR-1. But the potential was not achieved. The C4 was built with some inherent engineering flaws that simply kept it from ever achieving its promise. The flaws and the on-the-line fixes that were developed make it an extremely difficult car to develop. You have to find all the band-aids and remove them before you get back to the original engineering that was laid out. For example, although the car was quite well designed, the engineering flaws simply meant that the car would never stay in total alignment. If you were to step on the gas from a dead stop the (stock) car would go one way or the other. If you had a lot of horsepower, it would jump around unpredictably. To compensate, the cars were built with a "bind" in the chassis to keep everything as tight as possible.

It took us a long time to figure this out. We would fix one piece and something else would show up. It was a very frustrating experience to find the right set-up for the street versions of the G-350 and G-500 cars.

The C5 has been improved with a double wishbone rear suspension but a lot of the other problems remain.

Then, of course, we had problems with the engines as well. There are definitely some significant ignition problems in this engine. Again, the basic engineering works against the traditional fix-its. You will notice that most of the tuners don't really show radical increases in horsepower for the amount of money they ask. What happens is that they meet these same problems and just can't get past them. Callaway had a very successful program with his twin turbos; they built amazing torque so you got good pull. But they couldn't get the chassis to work. Same with the Lingenfelter C5, you can spend the money but the impact in elapsed times or lap speeds is variable.

When we started our G-350 and G-500 program, a couple of years ago, we were pretty much settled on going back to the big blocks to get the power we wanted. You have ample proof that this is the right answer since even GM has bumped the displacement of the LS-1 to 427 cubic inches on the C5-R. They thought they could use a lighter car with good aero to out-run the Viper, but they were wrong. With the rules they way they are, the Viper might have been limited on its horsepower output, but it had torque.

Today, with our new refinements, we are back to implementing the small block first. We can now get the power we want for three (3!) second 0-60 times and low eleven (11) second quarter miles. And, even with the small block, we can offer a handling capability that will simply blow bigger power plants into the weeds.

Let me focus on the chassis and suspension. We have done quite a bit more work in these areas. That's because once you fix that part, you have solved more than 30% of the tuner car equation. Once you have a platform, you can move on to develop more power and to make the whole car a more entertaining place to be. With our new chassis and suspension, the car is very easy to drive at the limit. In fact, its sweet spot is at the limit, even in the rain. The more you plant the throttle, the more the car responds to your commands.