This impeller has also been modified for more flow, with the vane angle ends turned in to
For many, the best solution is to have a converter built specifically to fit your combination. When doing this, even more data is needed, such as exact cam specs, cylinder pressure, race weight, head modifications, carb specs, and more. For an all-out drag car, Frank recommends that the stall speed be built for 1,500 rpm below the shift points, which will be based on the horsepower your engine makes. The way the engine makes that rpm is important as well. Does the horsepower peak come and go quickly, or is it a wider powerband? For a dragster with a balanced engine using rollerized internals, a high-stall, fast-reacting converter will be the choice since the car will be used only for racing and that motor can likely get rpm up very quickly. A street/strip door car with the same engine will lose some efficiency since it's heavier and will also lose driveability due to slippage; the converter on this car should be tighter (stall lower) to compromise between the two types of use. This car, which is in the 3,000-3,400-pound range, should stall at 2,000 rpm below the shift points. For a 3,800-pound restoration, a standard rebuild may be sufficient, but Frank notes that positive blade angles in a smaller converter will allow for a higher stall plus increased mileage, since the converter is constructed for more efficient fluid flow. The converter in this car should stall 2,500-plus rpm below the shift points since it will see very little, if any, track time. Frank tends to put less stall into street converters because "most guys drive more on the street than they care to tell you on the phone!"
For stroker engines pumping out 500 inches, Frank states that he still goes with a 9-inch converter rather than the 8-inch, even if the car is strictly for drag racing. Most stroker motors are not big rpm engines, and the larger converter with its reduced slippage will keep the rpm range lower, especially in the speed traps where the engine is maxing out. Unless you want to replace connecting rods and other parts, it's better to save the wear on the motor and give up some 60-foot time than going to a converter that's too small. Moreover, a larger converter will allow the car to hook up on a marginal track surface since the torque multiplication isn't as great. In a street car, the larger unit will also hold more fluid and, therefore, run cooler. Conversely, a bracket car may want more stall if only because atmospheric changes have less impact at higher rpm levels, making the car consistent. Indeed, higher stall converters are often used by racers in areas that are at higher elevations.
A selection of stators shows the wide variety of vane construction and design, all which w
Regardless of application, Dynamic uses a billet stator in place of a cast unit, and Frank showed us some new-age sprag components that are very small yet strong. The smaller the converter, the more serious the reinforcing must be; larger anti-ballooning plates and heavier welding are required. The smaller converter will also be more expensive because cores are harder to obtain. The old Opel and Vega cores used in the 8-inch converters are used up, and many later stock converters are not constructed with the same steel quality, meaning more reworking. The bottom line is to realize what your combination will need based on its mechanical construction coupled to its intended use.
"In my opinion, converters should be overbuilt," states Frank in conclusion. "The quality and time that a good company spends to create a converter really translates into less time spent tearing down the car to return and replace an average one when, not if, it breaks. The goal is to make and sell a converter that will last, to give the customer something he can count on when he's out on the starting line."