Why are pistons made from cheap forged or cast aluminum? That stuff is pretty weak and pistons do break from time to time. So why not make billet pistons? Obviously its not suitable for just trail type quads, but why not make them for high horsepower drag machines? Wouldnt it be alot stronger?

-Nick

 

are JE pistons Billet?

 

Nope, JE are Forged aluminum. The Billit piston Idea sounds good, but I'm sure there is a exspansion issues with a solid aluminum piston. Plus the cost. I'm just guessing though!![img]i/expressions/face-icon-small-confused.gif[/img]

 

I think you are really asking about materials. Let's start with the definitions.

Billet - Machined from raw stock
Forged - High pressure is applied to the part to make the shape.
Cast - Molten matertial is poured into a mold.

Cast Pistons are basically billet as your talking about them. Raw material is molten and poured into a mold that looks like the shape of the piston. The rough piston is than final machined. They will also pour ir out to form sheets, bars, and rod. They may also me extruded where they are pushed or pulled though a hole to form the finish size.

Forged Piston - The use high pressure to form the piston this compacts and changed the grain flow of the part and adds strengh. It is than final machined.

So both pistons are Billet as they are machined from a piece of aluminum, the differance is in CAST or FORGED. FORGED IS BETTER.

Smitty

 

smitty said it all perfectly![img]i/expressions/face-icon-small-smile.gif[/img]

 

Cast and billet are far from being the same. A casting is poured to a shape like you said, but a billet bars and rods are rolled to shape. It's the rolling that makes a huge difference in grain structure and strength properties.

It's true that casting is cheap, but I don't think I'd apply the term "cheap" to forging. It uses expensive dies to get parts to shape.

I think cost has a lot to do with why they don't machine pistons from billet. The results probably wouldn't be enough better to make a difference.

 

You are right bigben. Casting are more porous, brittle, have lower mechanical properties, and poorer grain boundaries that billet material of the same alloy aluminum. Heat treating also has an effect on yield and tensile strengths. I cant figure out why pistons arent made from billet. Read the aftermarket goodies list from the guys on this forum, I am sure there is a market for such parts.

 

When they make sheets and rods you are talking about either an extrusion or rolled product.
Sheets are normaly rolled between rollers to flatten and get the final thickness of the material. This will still have a linear grain.
When you extrude the raw material you push or pull it though ever decreasing holes. By doing this you don't add anything to the grain structure.

So a billet part would be stronger than cast but weaker than Forged.

When they forge the piston it is being forced into shape which will add some additional strengh to the part.

Smitty

 

BigBen -- Billet is "cut" from a block of whatever using CNC machines....