Can someone explain the difference on how they are made. We all know that forged are stronger but I wanna know the exact difference from a smart **** in here.

 

Wow...I would figure with all the talk about forged and all someone would know.

 

It's classified. Sorry.

 

Hypereutectic pistons use a silicon/aluminum alloy ratio that makes them very strong and stiff, although somewhat brittle. They wear well, and can be made lighter in this alloy than with more conventional aluminum alloys. They are cast. Forged aluminum pistons have a much greater tolerance for heat, and although they tend to expand more from cold, will withstand elevated temperatures better. They are less brittle and mechanically tougher.

 

search the internet...

Of course the forged vs. cast is easy.

Forged pistons are cut with machines from a blank of aluminum whereas a more economical to produce cast piston is, as the name implies, cast in a mold.

In the cast Al pistons Si is added to around 11% in stock el cheapo trim. When the silicone no longer dissolves in the melt at round 12% Si the mix reaches the "eutectic point". If you continue to add Si, the pistons become "HYPEReutectic". Up to 18% aluminum is used in some hp Hyper pistons.

So, hypereutectic pistons are actually "cast" as opposed to forged. Do you really need forged pistons? Probably not. They are heavier and expand in the bore more than a hyper piston.

Forged pistons can stand more overheating than cast pistons and have higher strength at temperature.

David Vizzard on the subject says,
"Because of the process and material involved, hypereutectic pistons are about as strong as forged pistons but can be run with much tigher initial clearances and wear much slower...."

So, would I want to run a heavier piston that well wear more rapidly than a cheaper hypereutectic pison? I will be just content runnging some Keith Black hyper's... just a high silicone content "cast" piston.

Take this information for what it's worth. Most of the above information can be found in print in:

"How to build max performance small blocks on a budget" by David Vizzard.

See his book for the unmolested explanation on pistons, but I hope this helps.

Ben T.

 

Sheeeeeet man. Now thats what I call an explanation. I know you took some time to write that buddy and I greatly appreciate it. You're a blessin to the board for ID's like me.

 

The other nice thing about hypereutectics...if they break, there's a good chance they won't take anything else out. I lost a piston last weekend down in Bowling Green due to detonation. My buddy tore it down and looked it over...it's really not much damage at all. Even the bore where the damage occurred stayed fairly smooth...nothing a quick hone job won't fix. Total repairs needed:

*New piston
*New rod (just a safety precaution)
*Valve job to clean up minor damage done from piston material scattering
*Mill a very tiny bit off the heads, just enough to clean the junk out

The other nice thing about the hypereutectics is that they're cheap to replace...only $25 per piston for me.

 

StudyTime made some good points. There might be a couple more:

The forged piston is not cut from a slug or billet of aluminum. That slug is first forged or formed into the basic piston shape.Forging forces metal into a die (like the "mold" for a casting), but under great pressure. The metal isn't molten, like in casting, so the grain in the structure "flows" as the metal is moved by the forging press.

This pressure makes the aluminum denser than the liquid cast part. Denser (more grams per cc) makes it stronger. Therefore, for a given piston weight, the forged piston is stronger. In fact, many forged pistons are considerably lighter than the cast (hypereutectic) pistons they replace. As rpm increases, piston weight causes the majority of the force trying to pull the rod apart. Ironically, you may need forged rods (also generally stronger than cast or powder metal (PM) rods) to withstand the high inertia loads generated by a cast hypereutectic piston which is strong enough to hold the hp generated, but heavier than an equivalent strength forging. There is rarely a "free lunch".

The forged shape is mostly evident on the underside or inside of a finished piston. The outside and top are almost completely machined. The cast piston usually has less machining done because it was cast in a "near net shape". Machining costs money. In most cases, diamond tipped tools are used on both types for final machining because they don't wear much and therefore can achieve very accurate control of size and finish.

The reason one uses a forged piston is for the strength necessary to withstand the horsepower being produced, and/or to get a lighter weight piston with a given amount of strength, and maybe as a safety factor for detonation or other nasty things which can occur in a very high output engine.

Yep, forged slugs expand more with temp, so the may be a little noisier when cold. Once again, "no free lunch."

If you don't need the things that forged pistons offer, hypers should do the job, and you can spend the money you saved on the heads.

My $.02