Into the 9s, Part 3

TH400 HEMI Transmission

Taking up where part two of this series ended, on our quest not only to get the MoparMax Maulin’ Magnum into the 9s but also to make it a consistent and winning race car, the factory NAG1 transmission had to go. Because the NAG1, like all modern automatic transmissions, is 100% computer controlled it never launched or shifted exactly the same way twice.

We had a mechanically reliable and robust NAG1 and the best tuning expertise available for modern HEMI cars. Our transmission was excellent for a streetable car that runs NHRA Summit Series Sportsman type classes at the drag strip. But we have moved up to the Pro type classes, where the reaction times and elapsed times have to be tighter. To be competitive we need to be able to do lap after lap with .020 or better RTs and run our number on command. And frankly, this isn’t possible with a NAG1; there is too much variability in how quickly it launches and when it shifts. We tell people that you can only suggest when you want a NAG1 to shift, not command it when to shift.

During the off-season this past winter the Magnum was slated for a slew of upgrades. Arrington Performance was building what turned out to be a 908 horsepower 426 stroker HEMI for the car. In anticipation of running faster than 10.00 seconds the car needed a lot of upgrades to meet the NHRA 8.50 certification requirements. You will be seeing other parts in this series on the engine build and RPM Rollbars upgrade kit that turned their 6-point bolt-in rollbar in our car into an 8.50 certified 10-point cage. But in this part, we’re focused on the transmission.

What we knew for sure was that we wanted a manual valve body race transmission in the car. Something that could not only hold up to the abuse of launching a 4,000-lb. car to hoped-for 1.29-second sixty foot times, but that would also be reliable and consistent. Now, since we’re Mopar people, our first thoughts turned to the trusty old 727 transmission. The bellhousing bolt pattern works with late model HEMI engines and the 727 is a Mopar legend. Why a three-speed instead of a two-speed transmission? Because of weight and speed. Two speeds work great in lighter cars and dragsters that can get quick launches and sixty foot times from the relatively high gear ratio (numerically low ratio) that first gear in a two speed usually provides. But, even if we put in a very low rearend gear to launch our big heavy Mopar with a two-speed, at the shift to the 1:1 top gear our engine RPM would drop so low on the shift that it would fall out of the power band.

We spoke with a lot of people in the industry and, frankly, we received a lot of varying opinions. So, we turned to our trusted friends at Westminster Performance Transmission for advice. WPT has always been bluntly honest with us and proven over the years that they not only built terrific transmissions, but that they also are a deep fount of transmission knowledge. And they are drag racers. If you ever get a chance you should check out their twin turbo HEMI headed big block Chevy motivated 200 MPH Top Dragster. They engineered the car themselves and have twice won NHRA Wally’s for Best Engineered car at national events.

WPT really made this easy for us. It all comes down to the transmission case, they said. No matter how good your internal parts are or how state of the art your builder is, the torque load has to be handled by the transmission case. Our current engine makes 908 crank horsepower and 866 lb. ft. of torque and there’s plenty of room for more in the future. Upgrades in 2017 could easily take the engine past 1,000 horsepower. In a heavy car that dead hooks its drag radial tires and runs in the nines, WPT told us that we need the strongest transmission case you can get. And apparently, that case is made by Reid Racing. The only catch is that it’s a GM style Turbo-Hydramatic 400 (TH400) case.

Now, we thought long and hard about this transmission. We know that we’re not the only power adder late model HEMI near or past the 1,000 horsepower mark. And we know that a lot of HEMI performance people read our magazine and look to us for advice. We wanted to build the ultimate, bullet-proof transmission that is possible to put into an LX/LC platform car with little or no modification to the car. After doing our research, we came to the conclusion that the case and bellhousing we wanted is made by Reid Racing.

Tipping the scales further in favor of the TH400 is the much wider array of parts such as gear ratios, valve bodies and more that are made for the TH400. Following Westminster’s advice parts that would go into our transmission included those from TCS Performance Products in Langley, British Columbia; Coan Racing in Kokomo, Indiana, and B&M Racing & Performance in Santa Rosa, California. Let’s start with Reid.