If your engine had a skeletal system the crankshaft would be the backbone of the body. Its job is to no not only make sure power is delivered to the driveline, but it also ensure the rest of the rotating assembly stays in place. We talked with Tom Lieb from SCAT Crankshafts about what you need to look for in an aftermarket crankshaft for your boosted LS-based engine.
The LS engine platform has been around for more than 20 years as a corporate engine, and it has found its way into everything from conversion vans to the Corvette. This makes finding these engines in the junkyards of the world fairly easy, but you need to make sure you know what you have for a block before you begin a high-horsepower build with boost.
According to Lieb, knowing the origin of the block needs to be priority number one before you even pick up the phone and start to order rotating assembly parts like your crankshaft.
“The crankshafts are different in the variations of the LS engine and that will change a few of the items you’re going to use on the engine. There are three different noses and that’s in relation to the timing cover, oil pump, and the cam drive. Whatever block you have its important to know the origin of it so you know which crank will fit. There’s also two different reluctor wheels for different electronics: the early reluctor wheels have 24 teeth and the new ones have 58 teeth.”
When you’ve established what crank you need it’s time to move on to look for in the crank itself.
There are many examples of stock bottom end LS engines making astronomical power because the stock crankshaft from GM is a strong unit, however, these stock crankshafts have their limits. The crankshaft from the factory is only made of high-carbon steel, so it won’t have the strength needed to take huge amounts of boost for long periods of time reliably.
Going to an aftermarket crankshaft for an LS-based application that will see a lot of boost will give you the peace of mind that it will last under strenuous conditions.
“Most aftermarket cranks are made of 4340 chrome moly steel and that’s an upgrade going in. It then becomes a question of the block itself you’re going to combine it with. The popular aftermarket stroke for LS engines is four-inches and what that ends up doing is giving you a lot of cubic-inch options. You can get a good ring pack and compression, so that will give you a solid platform for whatever you are trying to do,” Lieb explains.
Now some will question the need for an aftermarket crankshaft since a stock crankshaft can handle a good amount of power. The major differences between a stock crankshaft and an aftermarket unit are the material they’re made of and the heat-treating process used. Those two items are the difference between a crankshaft that can make big power a few times, and one that will stand up to extended amounts of horsepower-induced abuse.
“With an aftermarket crankshaft you have a chrome moly material that has been heat treated, it will be 30- to 40-percent stronger than the stock unit. Boost affects the fatigue life of any crankshaft. When you add boost you’re pushing down on the piston more during compression and you’ve got more cylinder pressure when the spark plug lights it off. That wiggles the crank and affects the fatigue life, so that’s why you go with a better material to fight all these forces,” Lieb says.
SCAT has looked at all of the various forces that a crankshaft has to deal with in a boosted environment and applied them to their LS crankshafts.
“The most important things for these crankshafts are the two things you can’t see: the quality of the material and the heat treating process. The strongest part of the engine is the crankshaft so the material and heat treating are so important. We want to be sure the crankshaft can deal with all the pressure being put on it. We also have made sure the position of the counterweights between the throws and the main on the crank are optimized. That weight and that position affect the rigidity of the crank at high RPM, so their shape and weight keep it together,” Lieb explains.
Before you start your first big-boost LS engine build make sure you know what block you’re working with to ensure you purchase the correct crankshaft. It’s also important to select a crankshaft that can meet your horsepower goals with the correct amount of strength. The last thing you want to do is try to save a few bucks on a crankshaft only to have it fail at the worst possible time under boost.