Hey everyone, I have been wondering recently why forged pistons are generally lighter than a cast piston. All dimensions being equal, the forged part should weight more because of more material being compressed into the given shape.

Do the forged pistons weigh less because of the higher strength, thus needing less material?

Thanks,
Chris

 

yes

Lightweight is good but don't forget that whenever you change any parts of the rotating mass that you need to get everything rebalanced.

 

Mostly the piston design and extra machining will make a forged piston lighter. The piston weight also has something to do with the HP level and application it's being used for. A 2bbl circle track motor has different needs compared to a 18psi Blown drag race motor. Piston weight in the same rod/stroke/bore setup between those could vary by more than 100g easily.

Better quality piston pins do the same thing. A stock LS1 pin is heavy, like around 150-160g I think. With a good pin you can get that down to 118g or less so you instantly save a bunch of weight there.

Pins (usually made of steel or Ti) and pistons (aluminum) also have different alloys for different applications. That can play into the weight also. All depends on what you are looking for.

Bret

 

Yes, listen to Bret. To elaborate a bit. You want the piston to be as light as possible but strong enough for the intended use and also at a price you can afford. Take a look at the JE catalog, for example. They list piston uses and weights. As Bret said, comparable size pistons for different uses can vary by up to 25% in weight. The more hp the motor will be making, the beefier the pistons and pins willl have to be when comparable mateials and design are used.

As far as cast v. forged, I don't have a reference right in front of me. But I doubt there is a huge difference in density. In fact, there isn't much weight difference between a high quality cast and a forged slug if they are intended for the same purposes. I'm thinking it has more to do with the extra maching and better design that goes into a high end piston.

Rich Krause

 

JE pistons are a good example. An all out JE race piston is very light and finely machined while the JE SRP pistons are made from the same material. They're heavier and don't have quite the same machine work. Both will work fine and the SRP piston is cheaper. If you need the lighter weight, you buy the race pistons.