What exactly is it? I understand people go with it for FI motors, but why? I just picked up a 75% complete turbo set-up and am planning on having the install donen sometime around summer-fall 08. Is this something I should seriously think about doing before or during the install? And if so, how much in "parts" does this typically cost?

Thanks,
Ryan

 

In laymans terms (I am not an engineer) forged parts are simply stronger and can stand up to greater force applied to them from F/I and hardcore race setups. The parts themselves are not "cast" in a mold but are "machined" down from a larger solid piece of steel, aluminum etc.. (making them stronger). This is a more expensive way to manufacture a part but the end product is much stonger and can stand up to much more stress and be more reliable in certain applications (ie.. supercharged, turbo and nitrous). I am sure you will get a much better answer than this from others much more knowledgable than I, but the gist is forged parts are simply stronger than cast parts and are necessary for reliability in certain instances.

 

"When a piston is cast, the alloy is heated until it is a liquid, and then it is poured into a mold to create its basic shape. After the alloy cools and solidifies, it is removed from the mold, and then the rough casting is machined to its final shape. When a piston is desired that is stronger than what simple casting can provide, they can be forged. This is when the rough casting is placed in a die set while it is still hot, and a hydraulic press is used to place the rough slug under a tremendous amount of pressure. This removes any possible porosity and also pushes the alloy grains together tighter than what can be achieved by simple casting alone, resulting in a much stronger material.

Hypereutectic pistons can be forged, but typically are only cast. This is because cast pistons are considered strong enough for stock applications, and the extra expense is not justified.

Aftermarket performance pistons made from the most common 4032 and 2618 alloys that are often used to replace stock hypereutectic pistons are typically forged."

Retrieved from "http://en.wikipedia.org/wiki/Hypereutectic_piston"

 

Whew! Some good info, some not so good above. No offense intended.

The casting process was described pretty well.

Forging is a operation where metal, say steel for a crank or rod, is roughly shaped from a bar or slug of steel, not a casting. The steel forging process takes place aroung 1500-1600 °F. The steel is literally hammered or pressed into matching dies under may tons of force. The hot steel "flows" into the nooks and crannies of the dies, and the grain structure in the metal stretches and shapes the grain pattern to follow the contours. This makes the part stronger and increases it's ability to carry loads. The forged blank is then machined to it's final shape. Often some of the forged surfaces are not machined, but in some cases the entire part is machined, and you really can't tell from looking if the part started as a forging.

Aluminum pistons start with slugs of rolled bar, not really castings. The slug is pressed into dies and, like steel, there is "grain flow". The forged part is generally more dense (the molecules are closer together) and stronger than the cast part.

A third way to make engine parts is to start with a round (or flat) bar of steel which has grain flow parallel to the direction in which it was rolled during manufacture. The part (crank, for example) is then fully machined from the bar. This might reduce a 450# chunk (billet) of 4340 (Nickel-chrome-moly) steel to a 40# crank. Machining away that 410# of steel isn't fast, nor cheap. This is called a "billet" crank because it started from a billet of steel.

The billet does not have grain flow around the webs, journals, throws, etc. like a forging so at first glance it might appear to be weaker. The beauty of using an Aircraft Quality (AQ) grade of steel is that it is very "clean" because it was melted in a vacuum and impurities, voids, tiny cracks, etc. are eliminated throughout the part. Forging is inherently a "dirty" process and can induce those kinds of flaws into the part. It only takes one tiny void in just the wrong place to make a forging junk. Magnafluxing doesn't find everything, but eventually the engine will find it and you may end up running over your own crank at 495 miles into a 500 mile race. Ungood!

So, in terms of increasing strength and longevity we have:

Casting
Forging
Machining from the solid (billet)

Not surprisingly the costs follow the strength. There's no free lunch.

Jon

 

Listen to Jon he knows what he's talking about.

 

Thanks guys, all these answers were great! I just dont typically understand alot about cars and didnt want the local shop to talk me into doing something I dont wanna do.. So, I'm just guessing, buying a short block from a sponsor would probaly come with forged internals??

 

Just call the sponsor and ask. Most of them will, but it's worth an extra 30 seconds on the phone to be sure.