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Well, according to what I know, hypereutectic means that the pistons are made out of aluminum, and have been super saturated with silicone, until a certain level of saturation has been met. I think 12% was the maximum amount of silicone that aluminum could absorb, and hypereutectic pistons run about 16%, or a 4% super saturation of silicone.
This extra silicone, adds a layer which sort of coats the outside of the piston.
Now, this sounds ideal to me, why would forged pistons be better then these magical wear-proof silicone impregnated pistons? How does 'forging' make the pistons stronger? I can't help but picture an old smithy hammering a crank and pistons on his anvil whenever i hear the word, "forged"... So maybe that's part of my problem.
Does anyone have any insight to this? Im just curious as to why forged pistons aren't hypereutectic. It seems like a good idea to me. Does it weaken the metal? Is it the fact that hypereutectic pistons are aluminum, and 'forged' are steel or something?
Just trying to learn more!
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They specifically make ceramic coated pistons if what you're after is a "coating" however hyper pistons offer the advantage (due to the mentioned silicon impregnation) of minimal heat expansion. They expand so little vs a cast/forged aluminum piston that the machining tollerances are much much tighter making for a virtually silent piston that seals better. Forged offers stricktly a strength advantage due to the forging process the molecules of the aluminum flow in a more consistant pattern increasing strength.
I may be off.... but i dont think hypers are designed with any form of "coating" or "wear proof" properties in mind.
My brother and I guy I know are running KB's. A 383 with 12.5:1 and a 327 with 12:1 comp. The 327 has been running for 4 years on the same pistons twisting 7800 RPM's at 10.90's in the quarter and the 383 for 2 years running 7.50's in the eigth. When I build my monster 355 with 6.0 rods I too will be running hypereutectic pistons. I have ran forged pistons in all my motors,
327 11:1, 360 10:1 ( 350 + .060 ), 462 12.5:1. I guess it comes down to are you going to be hosing it or not. If I were to hose it I would run forged pistons. I know this is not the answer you are looking for but just wanted to give some examples. The bottom line is the $$$$$$ and how much do you want to spend.
Like most people, i want to drop in a 350 to replace my 305, and eventually s-charge/turbo it. So i figure it's worth it to get a hyp build, then wait a few years for the s/turbo, and get a lower compression rebuild with forged parts.
i've read that hypereutectics shouldn't be used if you're making over 400hp
from scogin dickey's catalog:
__________________ '87 Burnished Copper Camaro LT. L98 with Pro Topline heads, LT4 hot cam, LT1 intake conversion. T56 trans and some suspension goodies.
hypers are basically a cast piston coated in silicon, they are a big step up from stock cast type pistons, but not close to as strong as a forged, but basically like stated, if your going to keep the engine all on horsepower, hypers will be fine, but if you ever plan to spray it or use any power adder forged is a must
Originally posted by TempesT68 hypers are basically a cast piston coated in silicon, they are a big step up from stock cast type pistons, but not close to as strong as a forged, but basically like stated, if your going to keep the engine all on horsepower, hypers will be fine, but if you ever plan to spray it or use any power adder forged is a must
Originally posted by tpi_roc (by the way no piston is steel)
Not quite true, steel was never used but lots of older engines(very old) used cast iron pistons, I rebuilt a 1930's Allis-Chalmer tractor engine and it had cast iron pistons, very heavy but the engine only turned about 2200 RPM max. Some cars used them up untill the 50's sometime.
If then for example I was running 350 to 400hp on motor and added 100 to150hp of nitrous on hypereutectic,would I be asking for trouble?Whats the max power they will handle,anybody running any real world combinations like this?
hypereutectic pistons are a cast piston, albeit alot better than your stock piston, they are cast with a much higher content of silicon, which gives them better strength properties. A forged piston is made with forging dies(alot like your old smithy analogy), which compresses and strenghtens and makes the grain flow alot better. A forging is WAY stronger, and more forgiving, than a casting. The hyper pistons also require a wider ring end gap, due to its heat reflective qualities, it wont transfer heat out as much, so the rings run hotter. This is a major reason that you can't spray them as hard. If you're not gonna lean on em to hard, they are a very good piston. Ive built alot of circle track, and mild drag motors with em, but If you're gonna work em hard(nitrous, high boost, etc) go with the forgings, or you will break 1.
just my .02 worth.
Bob
Hyper-you-cracked-it is what they go by in Ford circles (they come stock in the modular engine). My KBs lasted nicely in my 355 which was pushing 400HP. I'd never spray on them though... They tend to be brittle and more sensitive to heat+ stock ring gap = cracked piston top. Detonation kills them too Forged is a bit more forgiving, but it is heavier and shrinks/grows in response to heat. Many tend to be "clunky" when you first fire it up in the morning. They also suffer from a bit of blowby until they warm up too. Go with forged the first time IMO if you ever plan on a power adder at any time... it will save you $$$ and time
__________________ 2002 SOM z28 M6
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I think from an ultimate strength standpoint, the KB hypers and probably others are 'stronger' than a forging. Where the 2 differ is when the hyper reaches its yield point (the point where the structure of the aluminum in the piston is about to fail) it doesnt stay together, it breaks. A forged piston wont do that, it will deform past the yield state in an area thats called 'plastic' but it wont break for a little bit past there. The usefulness of this in a car is if the car is running right all the time, theres no problem. For those days that something is wrong (sorry Christos, thats you) the forged piston will take it and not complain as much. The hyper will just fall apart and screw up your engine.
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All aluminum pistons, cast or forged employ differences in their chemistry or alloy make up. The different aluminum alloys result in differences in physical properties, such as hardness at room temp, hardness at elevated temps, fatigue strength, coefficent of thermal expansion, wear resistance, etc. The physical properties, in turn, dictate to some degree the manufacturing process used to make the piston; cast, forged, their machinability, etc. This ultimately dictates the piston's cost relative to raw material & number of manufacturing steps, both for the casting or forging and the final machining. Hyperutectic reflects an alloy where the silicon content, I believe, is above 13%. The silicon is not a coating. Yes, steel piston currently exist in diesel engines. These pistons are of a 2 piece design with the piston head & ring groove portion is steel & the skirt section is aluminum. Both sections have pin bores & are coupled together with the piston pin. This desgin is also known as an articulated piston.
Get the forged piston. For a cuple hundred bux it's better now than later. If you convert from hyper to forged it will cost a lot more. I am getting Nitrous and now converting and losing big bux. The only disadvantage is, in cold temps I hear that the engine is kind of loud.
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FJK is right when he talks about the silicon content in all cast pistons. I just want to add one thing.
Ever heard of the term "saturation," in a chemistry context? "Hyper" pistons are saturated with silicon. This gives it the characteristic hardness (and unfortunately, brittleness). I believe the point at where a casting alloy becomes "saturated" is a little higher than 13%, tho.
Hyper is a cast piston, with EXTRA silicon added past the point where the silicon no longer dissolves into the aluminum. This isn't as bad as it sounds for strength.
Forged pistons are basically better because they are pounded (or "forged") into their basic final shape at high temperatures. This means that the grain (or molecular flow) of the base stock aluminum is unmolested, and therefore stronger.
Cast pistons have little very little grain from the base stock, because they are poured into a casting from a molten state.
If you've ever looked at what makes a connecting rod strong, the same basically applies to pistons. Making sure the grain, or molecular flow, is even and smooth is important to the strength.
So would a Cryogenic treatment of your pistons be worth it then? Anyone know if the hyper's would respond to this as well as forged?
cryogenic (freezing) treatment makes the metal sory of form a crystal-like pattern internally, and then after treatment, it's heated a few times, sort of re-forging it with the new molecular pattern.
Just a step up in molecular strength really, but if you hit up some 'hypers' with this, wouldn't they then be better than forged?
Im just thinking about less thermal expansion, mixed with super strength. Or is this overboard? I want to get a nice strong engine, with very strong components, but im not looking for a custom-cast titanium block or anything, if you know what i mean. ; )
Originally posted by gtabadboy The only disadvantage is, in cold temps I hear that the engine is kind of loud.
Im running forged in my 327...and it does chatter, especially in cold weather, until it warms up....note to self, get up earlier so car can warm up completly.
__________________ 1989 RS previous 2.8,
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It’s funny how TRW/Sealed Power forged pistons still get a bad rep for being “heavy” pistons. A lot of people consider the Keith Black hypereutectic pistons to be a light piston. I’ve compared the KB 400 flat top pistons to TRW/SP’s flat top pistons in weight. In the KB catalog I see the KB’s 400 SBC pistons range from 540-560 grams. TRW/SP’s #L2489F 400 SBC piston is rated at 540 grams.
TRW/Sealed Power is an excellent low budget forged pistons. They are a favorite with the turbo Buick guys. Very reputable engine builders like Duttweiler, Lingenfelter, Traco, Joe Sherman, etc. all sell TRW/Sealed Power pistons with some of their engine kits. If you don’t plan on making sustained power levels above 6000rpm, an ultra lightweight pistons isn’t necessary.
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Forged is a bit more forgiving, but it is heavier and shrinks/grows in response to heat. Many tend to be "clunky" when you first fire it up in the morning. They also suffer from a bit of blowby until they warm up too. Go with forged the first time IMO if you ever plan on a power adder at any time... it will save you $$$ and time 
