C3 Corvette Transmission - Maximum Overdrive

Installing An American Powertrain ProFit3 Five-Speed In Project C3 Triple-Ex

Dave Young Oct 21, 2010 0 Comment(s)
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Project C3 Triple-Ex began life as a manual-transmission '71, and since it was equipped with a T-10 four-speed, we were able to retain the bellhousing and relatively new clutch that came in the car. If your application requires these parts, they will be included in the American Powertrain five-speed conversion kit for your car.

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Since we had all the parts we needed for our conversion, we decided to take our Stingray to Inline Performance Specialists in nearby Webster, Florida, to make use of one of the shop's lifts. The job is no more difficult than installing a factory transmission in a Corvette, but because the fixed crossmember does require the rear of the engine to be lowered and the transmission to be at an extreme angle during installation, performing it by yourself with a transmission jack can be a challenge. Using an extra pair of hands, we found it easier for two people to lift the trans in place manually.

After bolting the transmission in place using the new mount and crossmember bracket, it took only a half-hour or so to bolt the driveshaft in place, hook up the speedometer and reverse lights, adjust the clutch, and reinstall the boots and console pieces. The professionals at Inline Performance Specialists had the factory trans removed and the new Tremec TKO bolted in place before lunch, leaving just the ancillary equipment to be hooked up in the afternoon. For the average mechanic in his own garage, the American Powertrain ProFit3 conversion could easily be accomplished in a weekend, if not a single day.

With the transmission installed in our Corvette, it was time for the fun part: testdriving the car. Having become accustomed to the long throws of our C3's original T-10 and its external shifter linkage, we were immediately impressed with the precision of the American Powertrain shifter. Gear selection resulted in precise clicks, with short throws between the gears. We hadn't even made it out of the parking lot, and we already knew this conversion was a great choice.

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On the road, we were even more impressed with the performance of our Stingray. The position of the shifter is just like it was from the factory, but accelerating through the gears tells you immediately that this is not a 1971-vintage trans. First gear of the Tremec TKO is noticeably lower, providing easy rapid launches and great throttle response. The remainder of the gears are nicely spaced in terms of ratio, all the way up to the 0.64 overdrive of Fifth. Prior to the American Powertrain conversion, our 350 would be spinning above 3,000 rpm to maintain a speed of 70 mph on the interstate. Now, we simply click the shifter into Fifth, and rpm at 70 mph drops to 1,900, making the car quieter, more fun to drive, and more fuel efficient as well.

As our project car has progressed, we've made major improvements to C3 Triple-Ex's aesthetics and mechanical hardware, resulting in a car that handles, stops, and accelerates better than it did when new. We must say, however, that the American Powertrain five-speed conversion is one of the most noticeable upgrades we've performed, improving the car in numerous ways and making it better suited to the more-powerful engine we have planned (see sidebar). Follow along now, and we'll show you the steps it took to convert our Stingray to five gears of fun.

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