Hypereutectic VS Forged Pistons - What I learned
For the most part I read many, many posts around the I-Net stating Forged Pistons are the way to go with strong power additions, specifically boost and NOS.
But I learned a little secret about Hypereutectics. Some are heat treated 390 hypereutectic alloy aluminum where others are Non-heat treated 390 hypereutectic alloy aluminum. The difference is how strong the hypers are.
Keith Black Hypereutectic Pistons are the heat treated ones. It seems the difference is crucial if one wants to use hypereutectics in a boosted application. this might explain why some people HATE hypers while others LOVE them.
The heat treated 390 hypereutectic alloy aluminum are actually stronger per weight then forged pistons. When making forged the casting is limited and requires additional work. The heat treated hypers do not need such extensive procedures and can use a permanent mold.
From what I learned, the heat treated 390 hypereutectic pistons are stronger then forged pistons under optimal conditions. Optimal meaning no detonation, no extreme hot spots, ect.
Hypereutectics also use much tighter clearances since they do not expand like forged do. Allowing greater ring seal, less piston-slap and greater longetivity.
Unless the engine is being built for really high boost/drag race application, hypereutectic pistons are the best for street performance boost. So as long as the tune is good.
In conclusion, I swapped my set of forged for a set of Heat treated 390 hypereutectic alloy aluminum pistons before I installed them. I will eventually put them under 15-16 psi of boost. I will let you all know how that goes. If I trash the block, oh well it's only a 3100. It would give me an excuse to get a 3400 and bore it out and put in reinforced crank with double timing chain and forged rods.
I would love to hear what your opinions are. I like to get into the serious science of performance engines. I don't want to just build the engine, I like to revolutionize.
10-09-2010 01:19 PM
Buyer beware, it appears you are quoting info from an advertisement that lacks specific detail as to what their idea of performance is. I would need to see proof that a hyereutectic piston is stronger than a forged piston. Mind you, there are different types of forgings, some of which permit close cylinder wall tolerances the same as hypereutectics.
Originally Posted by Schmieder
What I found:
"Hypereutectic 390 refers to a unique aluminum piston alloy that contains dissolved and free silicon. The material can be T6 heat treated to high strength and stiffness. Non-heat treated 390 hypereutectic alloy aluminum has slightly less strength than conventionally cast F-132 aluminum"
"Original equipment design is almost never suitable for performance applications."
"According to some sources, a "T6" heat treatment can increase strength up to 30 percent, but other engineers say this strength is not permanent: T6 is only stronger than T5 for the first 100 hours. A T5 heat treatment, on the other hand, gives a linear increase in strength over the life of the engine, which may be a better choice for many performance applications."
"One manufacturer said hypereutectic pistons can usually handle up to 1.5 to 2 horsepower per cubic inch of engine displacement. Beyond 2 horsepower per cubic inch, they would recommend upgrading to forged pistons." (Carley, 2005).
What I think; Hypereutectic pistons are stronger than cast pistons, but more brittle than forged and therefore more sensitive to detonation. Show me proof that Hyps are stronger than forged. Stock pistons are very good performers when their limitations are kept in mind. Many O.E. pistons have been subjected to and endured 15 psi. It's an add that was written who knows how many years ago.
You should do fine with stock. GM doesn't make pistons like it used to for the 60 degree motors, they make them better now.
Last edited by Joseph Upson; 10-09-2010 at 02:49 PM.
Where people lay down with HT pistons is that they neglect to adjust the ring end gap. It takes a little more ring end gap with HT because they hold more heat at the upper ring land causing more ring expansion than in a forged setup. Insufficient ring end gap when using HT pistons will destroy them. This mainly applies to the top compression ring and ring end gaps for the second compression ring usually remain spec. . . . . . . . . . . and coated skirts for the win.
If you ain't rock and roll, you must be driving a Honda
Ehh, more or less just stuff I read around. I heard both sides of the fence and both have there valid applications. I agree there is a place for forged pistons just as there is a place for hypers. The application also has a lot to do with which one is better. From what I found a street performer pushing 320 HP (for a v6 is good) the hypers are better due to longetivity and will rock around far less at cold start-ups then forged will. As long as the tune is good, the spark isn't overly advanced and the turbo pushes no more then 1 full atmosphere (14.7 psi) the hypers are far better suited for that application. I know anything over 15-18 psi needs forged internals all around.
Originally Posted by Joseph Upson
Thanks for your input.
Absolutely, I forgot about that but your right. I have been finding that IS a common over sight using hypers. But still the compression is better due to the tight clearances versus the wider allowances for the forged pistons with a wider gap.
Originally Posted by 86FieroSEv6
Has anyone tried the gapless rings yet? Do they really work well? I am willing to go that route if they are worth it.
You're still missing that there is more than one type of forging. Hypers are better from a cost effective standpoint in a boosted engine run within stock rev limits and moderate boost that's about it (especially in my case where the forged pistons are lighter than stock). 4032 forgings from my understanding run the same tolerances that the hypereutectics run and rock no more than the hypers.
The forgings used for competition need more tolerance and tend to scuff more in the bore during warm up, but that's not what you want to compare to, as they are not recommended for street use. 15-18 psi does not need or require forging all around, it would certainly be wise for the rods and pistons and that's considering cars we've read about here and on other forums. The second article I linked to states that some hypereutectics can run as much as 2hp cer cube before a recommended upgrade is made. Forged is where you go when you're at the upper limits of stock or just don't want to take any chances.
Here's an example for you, stock 3400 bottom end, 3500 heads, 18.5 psi:
I would be interested in seeing how it works out,I have been entertaining the idea of ht pistons for my 3.4 / 3400 turbo with a 14.7 boost max. and of course proper tune should be a paramount consideration no matter what piston is used.
Yeah, there is much I am still learning.
Originally Posted by Joseph Upson
I'll be sure to update how they work out.
Originally Posted by Hard Driver
The Pink Car
I'll agree... I just abused the hell out of mine and everything still seems fine. I'll find out when I take it apart this winter, If I even decide to pull the heads again.
Originally Posted by Joseph Upson
3500/3400 Hybrid, Custom Cam 216/240 .050 dur .517/.568 lift 112LSA
Ported, 3 Angle Valve Job, 65mm TCE TB, S&S Modified headers.
Stage-1 Raybestos/Alto 4t60e, 3600 RevMax Converter, EP LSD, 3.69FDR
firstname.lastname@example.org Chevy Fest, Epping NH Oct 2010 Nitrous 100shot
2007 Legacy GT Limited 5-speed 3" Turbo Back, Stage 2 - 255whp/310wtq