Section 8: Torque Converter Upgrades
How to Improve Launch
Switching to a higher stall-speed torque converter can provide the benefit of increased launch RPM and better low-speed acceleration. Once your vehicle is up and moving, though, a different converter will have little effect. Like any other performance tuning variable, converter stall-speed should be closely matched to your vehicle and power-train requirements. Also, a torque converter may not necessarily deliver the advertised stall speed due to differences in engine torque output and vehicle chassis conditions. After-market torque converters vary greatly in their quality and coupling efficiency. However, no converter should have to reach its advertised stall RPM just to back out of your driveway or accelerate in city traffic, as is a common misconception about higher-stall-speed torque converters. In fact, a properly designed mild after-market converter (i.e. 2500 RPM stall-speed) should not feel much different than its OEM counterpart in everyday driving.
Stall speed should be selected so that the torque converter will reach its stall speed just before the engine starts its power-band (when torque output begins increasing sharply). Too much stall RPM will actually slow a car down by wasting part of the engine's useful power curve. A stock torque converter in an AOD equipped Mustang will produce a stall speed of about 1800RPM, while the stock 5.0L H.O. engine enters its power-producing stage slightly later. Therefore, a stall speed of 2500 RPM is best for most stock and mildly modified 5.0L HO applications. If you have a 1994 to 1995 5.0L Mustang, their AOD-E torque converters stall at about 2300 RPM, which is a significant improvement over the early AOD. These converters will only work with the AODE transmission and will not retrofit back to the Earlier AOD. Vehicles with significantly altered valve events (i.e. large camshafts and/or huge valves) may benefit from stall speeds as high as 3000RPM or more depending upon configuration and torque curve. In such cases, it is best to consult your camshaft supplier or engine builder for optimum results.
For AOD transmissions (as well as C-4 and C-6 applications), there are a number of vendors providing high quality torque converters in many different configurations. As mentioned in the AOD Specific Upgrades section, Art Carr's converters require use of their special input shaft for the AOD and are available in a variety of stall speeds and sizes. Precision Industries also makes converters in both "lockup" and "non-lockup" varieties for the AOD, AODE, 4R70W, and E4OD with stall speeds to order. In the case of converter clutch style transmissions, such as the AOD-E/4R70W and E4OD, we rarely advocate removing the lockup clutch assembly from the torque converter. Retaining lockup provides maximum efficiency and versatility with no adverse effect on vehicle performance. Baumann Electronic Controls is a Precision Industries dealer and can provide you with a quality P. I. converter matched to your application. We have tried a number of different torque converters, and have seen the best performance and durability from the Precision converter. You don't have to just take our word for it. We suggest that you get objective recommendations from other performance enthusiasts and avoid using purchase price as the sole selection criteria. Search around and you will find that Precision Industries has a great reputation among converter manufacturers.