unknown_host

iTrader: (1)

Anyone here doing about 7psi of intercooled boost on hyperetectic pistons? Any probs with 9.5:1 compression and conservative timing?

Raiden

Hyper pistons can handle a lot. If you use nitrous, i was told by my engine builder that they have some sort of chem rxn and can be destroied during detonation and the chem rxn of the hyper pistons adn the no2. I'm runing 10psi with my hpyer's and have not problems! I have h20 injection, not an intercooler.

Ions91Z28

I'm no expert on this subject, but if I remember correctly....

Hypers are horrible underboost, not because of the actual boost, but because when detonation does occur, it will mess up a hyper piston faster than a forged, and I believe faster than even cast pistons. Boost doesn't kill the engine, detonation does. Keep the detonation down and you should be safe

If I remember correctly, correct me if I'm wrong here, Hyper pistons advantage other than price is the run tighter clearances. They are also harder than cast and I believe forged pistons. But due to the way they are made, detonation causes problems with them.

And someone please let me know if I'm wrong here, it's been awhile since I read about them.

88 WS6 TransAm GTA

iTrader: (1)

Hyper pistons are brittle, so to speak. Detonation, will in turn, shatter them, where a forged piston can "absorb" more of the shock from detonation.

BOTLFED

CJ over at www.toohighpsi.com is running low low 10's with hypers in his TT mustang..

As the others said, just watch detonation, and you're golden.

Cheers,

Ace_Murdock

actually, if i have this correct...

hypereutectic is just a term in metalurgy. a eutectic is a point on a graph of the temperature vs composition of various alloys. hypereutectic just has more of the material being added to the base. in this case silicon to aluminum (probably more than that).

without going deeper......i want to say that a forged aluminum piston actually has the same chemical composition as a hypereutectic piston. now the two differer in how they are processed. i believe a hypereutetic piston is just cast then machined right? if so, casting can create impurities and poor crystal structure to get optimum strength.

now forged will take the hyperetutetic alloy one step further. they "smack the livin daylights" out of it with large presses. this process deforms the aluminum and plays around with the crystal structure. after it is forged a material will have all of its "grains" in a certain direction, which inturn creates a stronger part.

now because forging is a process that goes beyond the yield point of a material, because of the way materials behave...the more you deform it the stronger they get, to a point (ultimate tensile strength).

so you smack your piston up when you make it. now while it is in use, in order to deform the piston you will need to have as much force as a forging press to deform it more.

correct me if i am wrong..

andrew

SATURN5

detonation will kill any piston..period,cast hyper,forged.

FWIW...Turbo Buicks have run 20 psi on stock cast pistons...
I have run 14 psi on cast pistons in the 305 without problems.

83 Crossfire TA

iTrader: (2)

To answer the jist of the original question, everything else being equal, hypereutectic pistons are the strongest of the 3 types. They are also the most dimensionally stable… the problem with them is that they are also very hard/brittle, so that if you apply an excessive force to them they crack and break apart.

Forged pistons are at the other end of the scale, they are also very strong, but at the same time soft, so if you apply excessive force (detonation), they just deform slightly and absorb the energy. Typically, in extreme applications it’s not that uncommon to find a forged piston that is beat to hell and still hasn’t flown apart taking the rest of the engine with it.

If you’re going to maintain a perfect tune, and never see detonation at WOT, you’d probably be best off running hypereutectic pistons (they’ll be lighter, expand less allowing you to run tighter tolerances… then a comparably designed forged piston), but as soon as you enter a situation where you might see detonation during a pass then the extra durability of the forged pistons is a good thing.

Andrew, you’re sorta half wrong and half right.

To keep things simple, hypereutectic just means that they have more silicon in them then what can be dissolved in the aluminum so it ends up in between the crystalline matrix of the metal. It’s a lot like when you put more sugar in your iced tea then you can dissolve in it, and you can see it floating around as you try stir it in. The end result is that the silicon prevents the normal expansion/motion of the aluminum and also wears slower then the aluminum.

When aluminum is beat up, it work hardens, it becomes more brittle and usually forms stress cracks also. The deal with forging is that it is squeezed at very high pressures into roughly the right shape while it’s molten. What you end up with is not only a denser (and heavier), much more consistent part, but it also lines up the grain structure which makes the part stronger while allowing it to remain fairly soft.

83 Crossfire TA

iTrader: (2)

To answer the jist of the original question, everything else being equal, hypereutectic pistons are the strongest of the 3 types. They are also the most dimensionally stable… the problem with them is that they are also very hard/brittle, so that if you apply an excessive force to them they crack and break apart.

Forged pistons are at the other end of the scale, they are also very strong, but at the same time soft, so if you apply excessive force (detonation), they just deform slightly and absorb the energy. Typically, in extreme applications it’s not that uncommon to find a forged piston that is beat to hell and still hasn’t flown apart taking the rest of the engine with it.

If you’re going to maintain a perfect tune, and never see detonation at WOT, you’d probably be best off running hypereutectic pistons (they’ll be lighter, expand less allowing you to run tighter tolerances… then a comparably designed forged piston), but as soon as you enter a situation where you might see detonation during a pass then the extra durability of the forged pistons is a good thing.

Andrew, you’re sorta half wrong and half right.

To keep things simple, hypereutectic just means that they have more silicon in them then what can be dissolved in the aluminum so it ends up in between the crystalline matrix of the metal. It’s a lot like when you put more sugar in your iced tea then you can dissolve in it, and you can see it floating around as you try stir it in. The end result is that the silicon prevents the normal expansion/motion of the aluminum and also wears slower then the aluminum.

When aluminum is beat up, it work hardens, it becomes more brittle and usually forms stress cracks also. The deal with forging is that it is squeezed at very high pressures into roughly the right shape while it’s molten. What you end up with is not only a denser (and heavier), much more consistent part, but it also lines up the grain structure which makes the part stronger while allowing it to remain fairly soft.

Ace_Murdock

i knew i had it somewhat right. I remember talking about all of this in my materials science class. i probably screwed up the terms.....as usual.

are you sure that you forge the stuff at molten temps? i remember reading about bringing the stuff to a red hot temp, not molten. If i remember correctly from my books, you start off with a billet of material, then smash it, smash it more, and so on.

so maybe i was 2/3s of the way right and 1/3 wrong?

83 Crossfire TA

iTrader: (2)

Well, you basically bring it just short of a molten puddle, while it is definitely plastic... BTW, aluminum melts before it reaches what most call red hot. Aluminum alloys typically melt in the 1100-1200* range and things start glowing red over 1200*

I’ll give you 2/3 right on this one

83 Crossfire TA

iTrader: (2)

Well, you basically bring it just short of a molten puddle, while it is definitely plastic... BTW, aluminum melts before it reaches what most call red hot. Aluminum alloys typically melt in the 1100-1200* range and things start glowing red over 1200*

I’ll give you 2/3 right on this one

Ace_Murdock

okey dokey