On the surface selecting a crankshaft may seem simple — a few journal measurements and a stroke number is all you need to get one fitted for the bottom end of your engine. But it’s more than that. Choosing a crankshaft that can handle the power your application will produce is one of the most important things when shopping for a new bottom end and is something that you need to pay attention to when selecting the best crankshaft.

Crankshafts are generally available in cast, forged, or billet steel for material choices. These cranks can have different machining processes done to them that will change their performance, but the biggest factor to look at when it comes to the crank’s strength is the material it’s made of. The material strength is what will keep a crank from breaking. The tensile strength for a cast crank is around 100,000 psi, with 140,000 psi for a forged crankshaft and 160,000 psi for a billet unit.

According to Tom Lieb at SCAT Crankshafts, you have to be realistic about the plans for your engine, because that’s what will set the stage for the crankshaft you need to choose.

“The use of the engine will dictate what kind of crank you should have. Every application is different and will change what you need. After you determine that, selecting the right crankshaft is very simple. The crankshaft is the strongest component in the engine and literally holds everything together. The crank is one of the last things that you decide on based on how you will build the engine, horsepower, and what RPM you will spin the motor to,” Lieb explains.

Photo Courtesy of Hardcore Horsepower

Even if you plan on building a mild engine, sourcing the correct crankshaft is critical. You may be fine using a cast crankshaft in the 400-500 horsepower range, but after that, you’d better start looking at a forged crank.

“Since you’re spending so much on parts you don’t want the crank to be the weak point. A lot of people get in trouble here because they skimp on the crank and if there’s a failure there it takes a lot of stuff with it. A good crank is a great insurance policy for the bottom end of your engine that will save you money if something goes wrong,” Lieb says.

A mild street cruiser and all-out racecar might have different power outputs, but both need the right crankshaft to avoid issues.

When it comes to the world of power-adders, getting the strongest crank possible is critical to support all the additional stress they place on the bottom end and rotating assembly of your engine. According to Lieb, it’s best to go big or go home. “You will want a forged crank at a minimum to handle all that stress, and if you really are going to be throwing the power at the engine, a billet crank is what you need. Putting the best possible crankshaft in the engine from the start in an application where you’re using a power-adder is really the only way to avoid any issues.”

Sourcing a quality crankshaft is a simple yet complex process that shouldn’t be an afterthought when building a engine. It’s important to be very realistic about what your plans are for your motor because that sets the table for your component needs. Remember, the crankshaft is the backbone of your engine and you want to make sure it can support all the abuse you plan to throw at it.