Pierce Peck; Beaumont, Alberta, Canada: As you're the Chevelle guy, you should be able to answer my questions in your sleep. I have a 1967 Chevelle with a 540ci big-block. I'm currently running a TH400 but would like to make the switch to a 4L80E. I'm already running EFI, using a Big Stuff 3 ECM, which has the controller for the 4L80E built in, so from an electronic standpoint, I'm good. My first question is: Will I need to modify my floorpan and/or firewall to fit the bulkier transmission? Second question: What will I need to do for the trans crossmember? Can my current unit be moved back, or will it need to be modified or replaced, and if so, with what?
Other info on the car: Dart Big "M" block, 10.2:1 compression, SRP pistons, Eagle crank, Scat rods, AFR 305cc heads, Edelbrock Pro Flow XT EFI, Lemons custom 21⁄8-inch headers, 3-inch Flowmaster mufflers, X-pipe, Edelbrock 2263 hydraulic roller cam, TCI Super Street Fighter converter, 9-inch Ford rearend with 3.89:1 gears and a Detroit Locker, with 275/60R15 M/T drag radials.
The car is intended for street/strip use, with the emphasis on being a very quick street car. It will never be used as a daily driver, but I would like to be able to take it on short highway trips.
Jeff Smith: We spent a long time looking around but did find a company called Performance Automotive and Transmission Center (PATC) that offers a 4L80E crossmember called the G-Force that's designed specifically for the early 1964–67 Chevelles. The crossmember can be found under PN RCAE-4L80E, and it sells for $259. As you are probably well aware, the 4L80E is a much larger, heavier trans than even the TH400. We have personal experience with our 1964 Old F-85 with a TH400 that the trans will sit very close to the floor. The 4L80E will probably fit, but you might have to tweak the floor in a couple of spots to make it fit with the proper driveshaft angle. If you want to take a shot at making your own crossmember, it appears that removing the welded-on mount for a typical TH350 or TH400 can be relocated on the front side of the crossmember to clear the transmission and still bolt up to the 4L80E. Since the new trans is 57 pounds heavier than a TH400, it might be a good idea to consider strengthening the old crossmember to support the greater weight of the 4L80E. This is especially important because the 4L80E mount location is 31⁄4 inches farther to the rear than a typical TH400. This places more load on the crossmember.
The obvious advantage to the 4L80E is the Overdrive, which is 0.75:1. In Overdrive, this effectively converts those 3.89:1 gears to a 2.91:1 rear gear, which will reduce your cruise rpm by 25 percent. We've spoken to a couple of performance transmission builders, and they tell us that the 4L80E integrates many of the aftermarket TH400 upgrades in the stock configuration, so right out of the gate, the 4L80E is stronger (although heavier). As you've also noted, the trans does require electronic control. For those who may not know, the Big Stuff 3 ECU that Pierce refers to also integrates transmission control with a very sophisticated EFI system that can run as many as 24 low-impedance injectors and do so for a very reasonable price. The base EFI system that also integrates the transmission control goes for less than $2,500. If the Big Stuff 3 name is not familiar, we can tell you that the men behind this are the same Meaney brothers, John and Leo, who were the co-founders of the original Digital Fuel Injection (DFI) system created in 1988. John Meaney was also the creator of several other name EFI systems over the years before creating Big Stuff 3 in 2003. It's beyond the focus of this story to go into the Big Stuff 3 system, but just know that many big-time drag racers use Meaney's system because the system works and is affordably priced. So, Pierce, you've make a good choice with the Big Stuff 3 system since it integrates the transmission control with the fuel and spark control.
Big Stuff 3; 248/887-5636; BigStuff3.com
Performance Automotive and Transmission Center; 888/877-1008; TransmissionCenter.net