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Switch-Pitch Turbo 400

1968 Nova
Posted March 17 2011 02:31 PM by Johnny Hunkins 
Filed under: Project Cars

Turbo 400 Switch-Pitch trans and converter

Phoenix Transmission Products builds us a really cool dual-stall converter and Turbo 400 trans.


We’ve turned to Greg Ducato at Phoenix Transmission Products before—most recently for the 700R4 overdrive automatic in our ’75 Chevy Laguna project. As we began planning for the 1968 Nova, I called Greg up to discuss different options with an open mind. In talking with Greg, I mentioned that the car came with a stock Turbo 400 and 3.08 gears. I commented that when we put the Dart 400 SHP motor in, the stock converter and highway gears actually felt pretty damn good. In fact, the Dart small-block had so much torque that we might be able to get away with the numerically low gear and no overdrive. Why not do a beefed-up Turbo 400 and keep the low gears? Greg liked the idea, but suggested we do something a little more exciting to spice things up. Why not dig deep into history a do a special build-up of a Buick Switch-Pitch converter?

Between 1965 and 1967, many full-sized Buicks, Oldsmobiles, Pontiacs, and Cadillacs came with a special Turbo 400 transmission, called a Super Turbine 400.  (See an excellent article on it here.) This featured a dual-stall torque converter that was electrically controlled to switch the stall speed between 1,800 rpm and a 2,400-2,600 rpm. This is done through a hydraulic circuit (controlled by a solenoid) that applies pressure to change the pitch of the converter’s stator blades. With minor mods, the pump housing of a non-BOP Turbo 400 could be converted to accept the Super Turbine 400 converter, and we’d off to the races! Greg suggested one of his PT400SX Turbo 400 transmissions (good for 700 hp!) with a short tailhousing for our Nova. He would beef up a Switch-Pitch converter so that it could take the Dart’s 533 lb-ft of torque, and modify both to work together in a non-Buick application.

The end result is that we will have two torque converters in the place of one; or said another way, we’d have the best of a race converter and the manners of a street converter in one unit. On the street, we will flip a switch that energizes the solenoid and applies line pressure to the stator mechanism. The low stall speed will improve our gas mileage and tone down the motor. At the track and at stoplights, we’ll flip the switch the other direction, and take the current off the solenoid. The de-energized circuit will change the stator blades to a high-stall profile for high-rpm launches and better torque off the corners.
 
GM’s Switch-Pitch has been around for a long time, but advancements in overdrive transmissions have meant that many hot rodders have forgotten about it. We think the Switch-Pitch could be a lot of fun and is worth a second look. Since our original discussion, Greg has built our Switch-Pitch converter and matching PT400SX Turbo 400 trans for the Nova. We’ll be dropping it in soon and wiring it up with the necessary transmission kick-down switch. (The converter pitch will change automatically as we accelerate from a stop too!) Keep an eye out for the print story sometime this fall. In the meantime, if you want to find out more about our Switch-Pitch converter set-up, you can call Phoenix at 817-599-7680, or log onto www.PhoenixTrans.com.



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