It's amazing what a simple...
It's amazing what a simple transmission swap will do to completely change a car's personality. The Chevelle went from a freeway-buzzy blunderer to a 900-mile road trip warrior.
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.
 Jaime Pacheo helped us with...  Jaime Pacheo helped us with the swap. We had previously drilled new crossmember holes in the frame to mount the TH400 (using a TH350 crossmember). Since the 200-4R trans mount is in the same location as the TH400, it bolted right up. In early Camaros, we've had to trim part of a TH400 crossmember to clear the trans pan, but it bolts right in. Just so you know, the rear trans mount bolts in a 200-4R are metric, at M10 x 2.5. |  We weighed the TH400 and the...  We weighed the TH400 and the 200-4R without fluid and found the overdrive to still be about 17 pounds lighter than the TH400. The added mass in the TH400 is almost exclusively rotating weight, which is why the 200-4R should, in theory, make us quicker on the track. |  The first install step is...  The first install step is to make sure the CPT 10-inch converter is fully mounted onto the input shaft and stator support. To double-check, lay a straightedge across the bellhousing face--there should be about a 1/4- to 3/8-inch gap between the converter mounting lugs and the straightedge. If not, the converter is not fully engaged onto the input shaft and must be installed properly or it will cause serious engine and/or trans damage. |
 The only major conversion...  The only major conversion work was to add this longer CPT slip-yoke (left) to make up the difference in the transmission length, which we measured to be 11/16 inch. The ideal way to do this would be to have a custom driveshaft made to make up the difference in length, but so far we've had no difficulties using the longer CPT slip-yoke. |  CPT owner Art Carr requested...  CPT owner Art Carr requested that we add an auxiliary cooler to the existing unit built into our Be Cool radiator. We had this B&M cooler for another project, so it will now go in front of the radiator, plumbed in series. This will ensure the trans temperature stays less than 200 degrees. | |