For many, building 500 horses isn't a problem; figure out what pieces will create the best possible combination, prep as needed, and bolt it together. However, once this is done, that power will need to travel through a variety of components before causing the rear wheels to propel the car forward. If you're using an automatic transmission, one of the key components is the fluid coupling between the engine and the transmission known as a torque converter.
The creation of a race converter normally begins with a junkyard core. The smaller ones come from four-cylinder cars. The housing is cut open and, if it passes inspection, the impeller/rear cover and front cover (where the converter attaches to the flywheel) are strengthened by welding on steel anti-ballooning plates to the center circumference. The vane, or blade angle ends, may be rebent for better fluid direction and rewelded for strength. A more positive angle will increase the impeller's efficiency by better directing the fluid into the turbine while allowing it to spin more easily for less slippage (static or negative angles built into the stock versions were more for smooth, non-shocking performance, but are actually higher-stalling due to their inefficiency). These pieces will then be sent to a furnace for complete brazing. An aftermarket stator with its one-way roller sprag will be installed for better strength, fluid dynamics, and torque multiplication. The flexplate mounting pads are attached to the front cover, and the rear or top cover, and snout are welded to enclose the assembly, and for Chrysler cars, the starter ring gear is attached.
Frank Lupo of Dynamic Racing...
Frank Lupo of Dynamic Racing Converters knows racing. When he's not at his desk on the phone with customers, he races his Super Stock Hemi 'Cuda in NHRA competition.
But how about in the real world? How do you know which converter will work for your car? We recently had a chance to sit down and talk with Frank Lupo at Dynamic Converter and Pro-formance Transmissions in Newark, Delaware. Lupo is a leading manufacturer of converters and a Mopar racer to boot; his NHRA Division 1 Hemi Super Stock cars are well known. We asked him to define the single-most important thing in selecting a converter for street/strip use.
"The first and most important thing you can do before making a converter purchase is to be realistic about what the car will be doing. There are always going to be compromises between performance and streetability. Durability is just as critical on a street car as on a drag car. Efficiency, how much the converter slips, is another factor, and, of course, with street cars, driveability comes into the decision. Personally, I'm a big proponent of not having enough converter on the street rather than too much."
There are any number of factors that can play into the converter selection, and Frank recommends that you talk with a knowledgeable builder when making this decision; it isn't a simple guess. Things that play into the selection can include usage, horsepower/ torque curves, car weight, rear gear (and transmission) ratios, and more. Frank says the more information you can give about the car, the easier it is to match the converter to the package.
"I want to know everything I can, because if I'm supposed to be building a converter to stall at, say, 5,500 rpm, and I don't know the collector size, the cam's lobe separation, the type of fuel (gas or alcohol) and other details, I'm stuck guessing. With these changes in the combination, that same converter might stall at over 6,000 rpm. I would much rather know ahead of time what I'm going to need than get a phone call later saying it doesn't work like I thought it should. There's an infinite number of variables, and each will have a bearing on how we construct that converter."