Whenever the conversation is related to crankshaft tech we are frequently asked “how much can my crank take?”. This is one of those questions that is very difficult to give a hard and fast answer to. There are just so many variables. Take crank materials. Most small block V-8’s come from the factory with cast iron crankshafts. Big blocks usually have forged cranks, which are stronger than their cast counterparts. But there are exceptions. Imports may have forged cranks, the Toyota Supra being notable for a very strong forged bottom end. So, from vehicle to vehicle there are differences. But we can give some general recommendations. Before we do, keep in mind that most crank damage is related to deficiencies in the block. If the main caps move, the crank will be damaged. Frank failures of the crank are (thankfully) rare and usually occur when a stock cast crank is used. Even good forged cranks may experience failure at the crank snout due to the load placed when a high-boost supercharger is installed. This is one of the circumstances where a good forged crank is very advantageous.
Some other generalizations to keep in mind are that revs as well as hp will add stress to the crank. Also, mileage plays a role. Accumulated fatigue over time kills parts. So, don’t expect to add a nitrous system to your 120,000 mile beater and get the same longevity as on a fresh motor. And in any case, you will not get stock OEM levels of reliability from a performance application no matter what parts are selected and how careful the assembly and the tune.
Stock cast iron crank: these are generally suitable for up to 50% increase in power over stock. In other words, if the base motor produces ~300hp, a blower or SC setup up to 450hp total may be used with a reasonable expectation of reliability.
Stock forged crank: these should be adequate up to a 75%-100% power increase over stock.
Over 75-100% power increase will need a high quality aftermarket forged steel crank. Excellent, high quality domestic cranks include Callies, Lunati, TFS, and others. If you are considering an import, we have had good luck with the Eagle brand in the moderate price range. Scat has imports at the lower end of their line and is another brand with a good reputation though we have less experience with them. Callies “Compstar” line consists of Chinese raw forgings that are finished and inspected in the US and are a good compromise between the unquestioned quality with a price to match for the good domestics versus the lower cost but lower quality imports.
One thing to keep in mind is that OEM cranks are often better than cheap aftermarket pieces. If you have good stock crank it may be much better just to keep it if the budget only covers a low-end aftermarket piece.
To learn about pistons for blower motors, click here.