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Overdrive Swap - Transformation

We Bolted In A California Performance Transmission 200-4R Overdrive In Place Of A Beastly Turbo 400 And The Result Was A Complete Transformation

Photography by Doug Roe, ,

Queen said it best: "I want it all, and I want it now!" The 21st century automotive version of immediate gratification stars our Orange Peel 383-urged '66 Chevelle as the underachieving street car. Sure it had high-11-second strip cred, but its freeway skills were lame. With a Turbo 400 three-speed auto and 3.55 gears, we were making lots of rpm and noise and getting nowhere slowly. We could have yanked the gear out of it, but that would have killed our 11-second dragstrip escapades. We wanted it all--to drastically reduce our freeway cruising rpm, improve the Chevelle's miserable single-digit fuel mileage, and run quicker at the digs. Sound impossible? Not really. The solution came in the form of a simple bolt-in silver bullet: a California Performance Transmission (CPT) 200-4R overdrive automatic.

Normally, we'd make you wade through the whole story for the results, but frankly our Chevelle's one-day gearbox swap was a home run. By just substituting a CPT 200-4R and a nonlockup 10-inch converter, the Chevelle transformed almost immediately. Our Buddha-belly "before" picture had the Chevelle screaming at 3,200 rpm at 70 mph. And even at that speed, we were in danger of being run over by Hyundais and the occasional aggressive left-wing Prius. The slim-and-trim "after" swap picture has our Orange Peel Chevelle as a kick-butt freeway flyer cruising effortlessly at 72 mph at 2,200 rpm. We took it to the dragstrip and on the first pass improved our eighth-mile times by 0.10 second with no other changes. Then we demon-tweaked the carb and on this year's Anti-Tour trip to Phoenix knocked down 14.3 mpg for 900 miles. There were some little tricks that made this whole effort possible, but the real story is that with a CPT overdrive trans, you really can have it all right now.

Why We Chose a 200-4R
Back in the Mar. '09 issue, we showed you why a 200-4R is an excellent choice for an overdrive automatic, as well as the modifications that California Performance Transmissions goes through to make these boxes even stronger. But there's more to the story. We started with one of CPT's performance transmissions treated to all the good mods. What makes the 200-4R such a great choice is that it will bolt right in place of a TH350, Powerglide, or, in our case, a TH400. The transmission case lengths do vary slightly between these transmissions, but even that's not a deal breaker. The important point is that the 200-4R places the trans mount farther back than either a Powerglide or a TH350. But because we had already moved the crossmember in our Chevelle to mount the TH400, the crossmember bolted back in with zero drama. The only other hurdle was replacing the large Turbo 400 slip-yoke with a slightly longer CPT slip-yoke to make up for the fact that the 200-4R is roughly 11/16 inch shorter than the TH400.

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