Turbochargers for Automatics
Many people wonder if it’s a good idea to put a turbocharger on a car with an automatic transmission.They’ve heard horror stories that it will mess up the transmission in no time.
A great many turbocharged performance cars have automatic transmissions in them. The old school Buick Grand National and GNX only came with automatics and they were plenty fast. Audi puts out a number of turbocharged cars with automatic transmission, and so does Porsche. In fact, many high-horsepower cars on the road today come with an automatic transmission including Jaguar, Bentley, Corvette, Infiniti, BMW, Mercedes Benz, and many others. The Bentley is particularly noteworthy because it’s 412-cubic inch turbocharged V8 slams well over 600 ft./lbs. of torque through an automatic transmission.
Many people are under the misconception that automatics are weak, when the fact is that their basic mechanical elements are strong, and in some cases, stronger than a manual transmission. Automatics use planetary gear sets instead of meshing only two gears at a time as a manual transmission does. Planetary gear sets are actually made up of six gears that are in constant contact with each other. This eliminates the need for synchronizers, and for meshing and un-meshing the gears when a shift is required. Additionally, because torque is absorbed through multiple gear contact areas, a planetary gear set can be made smaller and lighter than standard transmission gears and still maintain very high levels of strength.
The thing that kills automatic transmissions is heat. Heat is generated from a number of sources in the transmission. The multiple clutch packs (usually four clutch plates in two separate packs) in automatic transmissions generate a lot of this heat, and because they are designed to slip to provide comfortable, smooth shifts, they can wear prematurely when a lot of power is put through them. The cure for this is to install a shift kit to increase the hydraulic pressure applied to these clutches to allow them to hold more firmly and to slip less. The transmission will shift harder, and more noticeably, but will generate less heat and last longer under high power abuse. A good transmission oil cooler will also be a big help in allowing an automatic to live under abusive conditions.
One more thing in the automatic’s favor is shift speed. No matter what anybody tells you, an automatic shifts faster than any manual, no matter who is rowing the gears. Additionally, power flow is not interrupted like it is when you step on the clutch in a manual equipped car. Sure, some people can shift manuals without hitting the clutch, but those gearboxes won’t last long under all that abuse.
You may have noticed if you follow import drag racing that some teams are switching over to automatics in their mega-horsepower race cars. The reasons are pretty simple, less breakage, more tunability, and more consistent performance. Sure, manual transmissions are fun to drive, but automatics are up to performance applications with the proper preparation.