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Case study: Alloy selection for use in professional dragsters

In the world of professional drag racing, it is very common for the race car engines to utilize a belt driven supercharger. This supercharger is installed on the top, or the induction portion, of the engine. The supercharger runs at very high speeds and forces air and fuel into the engine. This allows the engine to produce much higher horsepower. The “king of the hill” classes in professional drag racing are Top Fuel Dragsters and Top Fuel Funny cars. These cars use a fuel that is up to 90% nitromethane. The engines in these cars can produce close to 10,000 horsepower and can power them at speeds reaching over 300 MPH in a quarter mile.

The challenge for Nevada Heat Treating and our customer was a gear on the supercharger which was failing in use. The rotor speed for supercharger and this gear can reach over 12,000 RPM during a race. This gear was made from a common tool steel which could not handle this incredible rotational speed and force, and the heat treaters solution of using metal hardening processes would not work. A fairly simple solution, but unacceptable for this application, would be to make the section of the gear that was failing thicker than the original design. This would produce a robust part. Why this is an unacceptable solution simply comes down to added weight. Weight is extremely important in all forms of car racing applications. This weight is even more critical on a rotating component like this gear that has to spool up to 12,000 RPM in a matter of milliseconds. Consulting with our customer, as well as using our internal metallurgical resources (rare among heat treaters), led us to select an alternative material that would perform better than the original tool steel without any weight penalty. The material that was chosen was a modified version of a Cr-Mo steel. Experimental parts were machined and subsequently heat treated at Nevada Heat Treating. After secondary processing, the parts were ready to be installed and tested. The results were extremely positive and passed all of the design criteria and the part was more durable than if metal hardening alone had been used.