Which piston is better? Hypereutectic or Forged? Im startin my 383 builld and I plan on 150 or so shoot of nos and down the road a s/c.

 

Forged, if you're using a power adder.

 

 

nothing but forged if u want anything 2 last.

 

With a power adder. For N/A street use, hypereutectic is better.

 

interesting, im new to the engine building world too, but why is hyp better than forged for n/a. Im going n/a, and kinda being the noob assumed forged is more expensive so it must be better

 

Hypereutectic pisons expand less with heat, so there's less cylinder wall clearance when they're cold for less piston slap and longer life.

Hypereutectic pistons will fail in a hurry under detonation when something goes wrong with a power adder though, so forged is preferred.

 

Makes sense, so I'll be fine with hyp pistons on a N/A motor then. Any huge difference in weight or friction? I guess this isnt the right section to be posting for it, but while were on the subject

 

Kind of depends on the piston.

 

Actually for mild FI and Nitrous App's Hypereutectic pistons would be fine....BUT its that bug....Why build a motor for Mild if that s where you want to START.....because we all know the Bug takes control and more is needed......then you wish you went Forged

 

Yeah it's always tempting to put another 100 HP of nitrous, or a few more PSI of boost in. Actually hypereutectics would be fine even for not so mild applications, but if it knocks just once you'll kiss something goodbye.

 

Yes, a good tune is always needed but at the same time detonation will destroy forged pistons as well...just takes a couple more times....hyper. pistons are a little more forgiving than that tho.....less than forged but a lot more than cast.

Personnally My choice is forged because I have the "bug". Hypereutectic would be fine for someone who cant afford the high price of forged...but the need to remember that they couldn't afford big results.

All in all...."Best pistons" also fall in the "best piston in my budget" category, which falls into the "I can only afford to go this fast category".

 

(the following requires imagination)

Forged or Hypereutectic?

The best macro-scale analogy I can think of for the difference between forged and hypereutectic aluminum pistons uses wood. Think of a forged piston as an extremely knotty log and a hypereutectic piston as a high quality/multi-layer piece of plywood. Also, think of a lean condition as a torch and detonation as a JACK HAMMER. For anyone who has ever split firewood with an axe, you know it could take 20 swings to get through a big, knotty log. If you hit plywood with an axe/hammer it tends to split at the glue and break all at once. Plywood is surprisingly strong due to its composition and multiple layers, and knotty wood is tough because of the hard knots that resist splitting and the twisted grains that circumvent the knots. Now pretend you were jack hammering or burning both pieces of wood. They burn at about the same rate, but the knotty log withstands the jack hammer for an extra minute or so.

The crystaline (micro) stucture of forgings and hyperuetectic castings are directly analogous to the above types of wood.

However, plywood is more expensive then those knotty logs you see on the side of the road marked "FREE FIREWOOD" (because someone else didn't feel like splitting them). So its not a perfect analogy, but mechanically it is pretty close.

 

Alright, thanks to all. Didnt expect to hear so much so soon, Thanx for answering my question and even learned a few new things.

 

Yuck, that’s an ugly analogy…

Hypereutectic pistons are made of an alloy that has more silicon added to it then what can actually be dissolved in the aluminum, so the silicon that does not dissolve forms it’s own structure in the aluminum item (more like the knotty log really).

That extra silicon makes the piston VERY strong and very dimensionally stable, much more so then forged or cast. This makes them the best choice for street type use since you can fit them much more tightly preventing cold start up issues, excessive wear, better oil control…

The only problem with them is that that structure makes them very hard and brittle so when something does go wrong and causes detonation they are more likely to crack and fall apart.

Forged pistons are usually made of a more normal heat treated alloy which has been forged (compressed/hammered) into shape making for a denser piston structure. They tend to be heavy and reasonably soft, making them not as nice in street type use but when they are hit with detonation, they deform slightly rather then break, so if you run into bad detonation they can live for a little while before they let go. As quality and price go up they tend to get better WRT to weight and machining to be more dimensionally stable.

If you’re religious about tuning and it really is a street car, you’re probably better off with a high quality hypereutectic piston, even in high hp applications or with a power adder, the trick is to make sure that you don’t let it detonate. They are also pretty popular in a lot of real race engines like road race and circle track.

Forgings are justified when you know you’re going to be running the engine at the ragged edge, if you know you’re going to see some detonation it’s the only way to go.

Of course, this is all relative, you’d be surprised how many people run 9’s and 10’s on stock type or worse cast or hypereutectic pistons, and I’m continually shocked how many 13, 14 15… second cars are built with killer forgings…

 

Too funny. Back in the day I built one of those 13 second cars with forged pistons. Today I have car that puts out more HP and uses hyperuetectic. Both are in the relatively low horsepower range. The difference was that the forged piston engine really needed them because I didn't have much of an idea of how to tune.
I would like to think I have a better grasp on tuning and that is why the newer engine uses hyperuetectic pistons (not to mention they were already in the block).

I have been looking around for dish pistons to use with a stock 400ci crank, 5.7" rods, 406ci block. What I have been finding is that there are more dish pistons available in hyperuetectic than forged. And the price varies a lot.

BTW, Keith Black and other pistons companies have a lot of good info about forgings and hyperuetectic piston composition.

 

Eutectic refers only to the amount of silicon present in the aluminum to make it a homogeneous or non-homogeneous material. forging is the manufacturing process used to make the metal better than cast. There can be |||forged hypereutectic(rare) or cast hypereutectic(installed in most post 80's cars FROM THE ASSEMBLY LINE, because it reduces emissions), forged eutectic(common) or cast eutectic(common in cars before 80's), or forged and cast hypoeutectic(both common in diesel engines because of durability, AND RESISTANCE TO DETONATION, downside is that engine only can operate within a certain temp range which prevents cold stress i.e. you must warm up)|||. There are however heat treated cast pistons that are are a tad more resistent to damage, and i think that is what you are talking about.

 

BS and you agree with what???

My response was both technically correct and answered the question. Throwing hypoeutectic alloys into this discussion needlessly complicates the issue and a proper discussion would have to involve melting temperatures (melting/freezing points and crystalline structures formed...), all of which are pretty much irrelevant since I don't believe that anyone actually makes hypoeutectic pistons for gasoline engines, at least not available small block chevys.