Inliners International Forums General Discussion Drive Train recommended rear end ratio

Torque Converter Stall Speeds


To explain "stall speed", let’s start with a true full stall. If the transmission were in drive, the brakes were held down (so the vehicle will not move) and the throttle was held "wide open" the torque converter will "stall" the engine at a certain rpm. When "stalled" the engine will not be able to spin any faster unless the vehicle is allowed to move. This is a true full stall. We have specialized equipment which is used to perform this test.

DO NOT TEST FOR TRUE STALL, IT CAN DAMAGE SHAFTS AND OVERHEAT THE TORQUE CONVERTER!

The next stall speed is generally called "break away" stall speed. If a truck is stopped on a hill and held in position using light throttle as opposed to brakes we are almost at the "break away" stall speed. If the engine rpm required to "hold" the truck was 1100 rpm and an increase to 1125 rpm started to move the truck then the "break away" stall speed is 1125 rpm.

The last stall speed is generally referred to as the "flash stall" speed. The flash stall speed takes effect under hard acceleration. If, from a standing start, you were to "floor" the throttle the engine would start to accelerate quickly and then pause at an rpm is it starts to pull the truck. If the engine went from idle to 1500 rpm in 1.5 seconds when floored and then took another 2 or 3 seconds to get from 1500 to 1700 rpm, this would mean the "flash stall" speed was at 1500 rpm. When we lower the stall we want to lower the break away speed as well as the flash stall speed. This will make the engine work at a lower rpm for a given road speed and, in most cases, will increase fuel mileage.

Once up to speed, the computer will command the lock up clutch "on", and the driven fan will lock to the front cover of the converter. At this point the drive, driven fan and engine are turning the same speed which means all engine power will be delivered to the transmission and back to the wheels.