Forged vs. Hypereutectic for turbo applications

This is likely to start some sort of war, but I'm going to ask anyway.

I'm planning my next motor, and it's going to be a twin turbo LS1/LS6 setup. It will see only street use, and perhaps a 1/4 mile run a few times per year. I'm angling for about 450-600rwhp with a stock displacement setup.

Now, I like a dependable, low maintenance engine that doesn't use a lot of oil and doesn't make a lot of piston slap noise. Hypereutectic pistons are usually lighter than forged pistons and can run tighter piston-to-wall clearances, but all I have heard for years from the "pros" is that if you're doing a performance motor, you gotta go forged. Hypereutectic is for weenies.

Well, I decided to call up Keith Black Pistons and see what they had to say on the matter. Turns out, they say that you can go with hypereutectic pistons even in extreme applications, so long as you get a good piston and keep it within the expected torture range. Apparently, the big problem most engine builders have with hypereutectic over forged is that hypereutectic pistons tend to fail spectacularly, shattering or exploding, whereas forged pistons tend to deform somewhat more plastically with less drama (but a ruined cylinder regardless).

So what do you guys have to say on this? I'm betting most of you have gone forged simply because "that's what everyone's always done." Is this true? Has anyone had any good/bad experiences running hypereutectic pistons on performance applications?

There's a pretty big difference in the "abuse" a piston gets from 450 rwhp to 600 rwhp.

LPE has done (for C5 Vette) just about what you are planning. Their 550 hp(fw) used stock internals, from what it says on their website. 650 fwhp version uses forged internals. That makes lots of sense to me, and LPE does a pretty good job of matching components to their intended use.

Figure out where you want to go with hp and rpm, and build the bottom end for that. That applies to any power level.

FWIW, hypereutectic pistons aren't necessarily lighter than many forged, especially in the same power range. They are less dense, but it takes more of that less dense material to equal the strength of a more dense, stronger forged piston.

My $.02

So what do you guys have to say on this? I'm betting most of you have gone forged simply because "that's what everyone's always done." Is this true? Has anyone had any good/bad experiences running hypereutectic pistons on performance applications?
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hypereutectic piston will work OK

but you have to account for piston top's greater heat

might be small additional problem as boost is increased too quickly for octane amount and RPM

some of Forged pistons like TRW or SpeedPro
you could take an old piston and throw it as hard as you can against concrete and only deform it , not crack it.

and some other type "Forged Alloys" will crack under same test

the problem is more your "TuneUp"
you never want to get to point where
either hypereutectic or forged piston cracks or overheats

I don't think what you are planning is an appropriate platform for experimentation, so I recommend going with what is known to work. IOW, get a good set of forged pistons. Of all the engine parts they are the last place I would try to "get away with" anything on a forced induction motor. AFAIK, even the penny pinching OEM's use forged pistons on factory forced induction motors.

Rich Krause

I thought everyone would be recommending forged for anything over lawnmower HP levels. On most boards that's the recommendation you would get. I'm glad I'm not the only fish trying to swim upstream against that current here.

I have pushed Keith Black hypereutectic slugs to about 550HP (flywheel) on nitrous without ever a problem. I currently use them in my 383 roots-blown motor and make about 480-490 at the crank in a very "streetable" combo. No problems to report in the blower motor in the last 2 years.

ANY piston will eventually fail under detonation (THE #1 killer). Forged pistons will just last a little longer than hypers before they give. In a boosted motor the first sign of detonation is usually when the motor lets go. You just can't hear the "rattle" over the exhaust and the blower screaming. And detonation in a nitroused or boosted motor does it's damage MUCH more quickly to the internals than in a N/A application.

Weight of a hypereutectic slug really depends on how it is manufactured. Just an off-the-cuff sampling.... A stock cast flat-top 350 slug will be around 600g. A half-decent Keith Black hypereutectic slug will usually be around 550g. A piece of crap Speed Pro hypereutectic can be 650+. Forged slugs are all over the board- they can range from battleship-heavy TRW cheapie forged units to wicked-light exotic race pistons that dip well below 500g a piece.

Originally posted by rskrause
I don't think what you are planning is an appropriate platform for experimentation, so I recommend going with what is known to work. IOW, get a good set of forged pistons. Of all the engine parts they are the last place I would try to "get away with" anything on a forced induction motor. AFAIK, even the penny pinching OEM's use forged pistons on factory forced induction motors.

Rich Krause

:confused: Those penny penching OEMs use cast hyper pistons with MUCH, MUCH, MUCH more frequencey than forged pistons on FI motors. All those mopar 2.2 turbo motors in the 80's and 90's used cast pistons, as does the new turbo neon SRT4. Subaru uses cast pistons in turbo applications, even in their high output STI. Turbo buicks used cast pistons. VW and Audi have switched from forged to cast pistons in their turbo motors several years ago. Oh, and lets not forget turbo Supras, which also have used cast pistons for the past 3 generations (maybe even 4 generations, but I don't know anything about the mk1 supras)- some of which have seen triple their factory hp.

This is not to say that OEM cast hyper pistons designed for N/A use will be adequate for FI setups... in most cases, they are not. On the other hand, a good quality cast hyper pistons like those made by KB (assuming a safe compression ratio, tune, and octane) will work great with FI setups.

Originally posted by EddieP
:confused: Those penny penching OEMs use cast hyper pistons with MUCH, MUCH, MUCH more frequencey than forged pistons on FI motors. All those mopar 2.2 turbo motors in the 80's and 90's used cast pistons, as does the new turbo neon SRT4. Subaru uses cast pistons in turbo applications, even in their high output STI. Turbo buicks used cast pistons. VW and Audi have switched from forged to cast pistons in their turbo motors several years ago. Oh, and lets not forget turbo Supras, which also have used cast pistons for the past 3 generations (maybe even 4 generations, but I don't know anything about the mk1 supras)- some of which have seen triple their factory hp.

This is not to say that OEM cast hyper pistons designed for N/A use will be adequate for FI setups... in most cases, they are not. On the other hand, a good quality cast hyper pistons like those made by KB (assuming a safe compression ratio, tune, and octane) will work great with FI setups.

I think my info must be out of date then?? I still wouldn't use cast psitons though.

Rich

Originally posted by rskrause
I don't think what you are planning is an appropriate platform for experimentation, so I recommend going with what is known to work. IOW, get a good set of forged pistons. Of all the engine parts they are the last place I would try to "get away with" anything on a forced induction motor. AFAIK, even the penny pinching OEM's use forged pistons on factory forced induction motors.

Rich Krause

Rich, it has nothing to do with pinching pennies, trust me. I'm not willing to cut a dollar anywhere so long as that dollar's well spent. The goal of this project is to have a 500rwhp 'Vette that is just as reliable and maintenance-free as a stock 'Vette. I could probably get this with a normally-aspirated larger displacement motor and a radical cam, but I want this thing to be a smooth sleeper. No barking exhaust. No lopey cam. No piston slap. No sewing-machine-noisy valvetrain. And above all, no excessive oil consumption.

Forged pistons require more piston/wall clearance than hypereutectic, meaning more blow-by (bad emissions), more oil consumption (as if the LS1 needs more of that), and more piston slap when cold (another existing LS1 problem even with stock pistons). I don't want any of that, I just want the extra horses.

Originally posted by rskrause
I think my info must be out of date then?? I still wouldn't use cast psitons though.

Rich

Rich, not that I'm trying to pick a fight or anything, but why would you say such a thing? Clearly cast pistons can handle the stresses involved so long as they are designed for that abuse, because OEM's have been doing it for years in turbo and blower cars.

I mean, I wouldn't put a bone-stock cast 350 SB Chevy piston in a 600hp blown nitrous car because that's silly, but if KB made a piston specifically engineered to handle that kind of stress, why wouldn't you use it? Especially if there might be advantages (weight/cost/clearance/etc.) to doing so? You see, this is exactly the kind of thinking I'm trying to question. I've received a ton of "you need to use forged," but when asked why, all I get is "well, I'd never use a cast piston." I'm sorry, but that's just not a sufficient answer.

KB's hypereutectic designs have been repeatedly run in nitrous, turbo, and blower cars with no abnormal failure rates. Lingenfelter's getting 550hp on stock LS1 internal cast pistons (although I wouldn't trust that in my car simply because I don't think GM designed that much of a safety margin into their pistons).

I guess the question boils down to this: it's not whether you would use a hypereutectic piston, it's whether or not you have used one (or know someone who did) and had bad results. Everything else is just old wives tales.

Originally posted by prisoner881
Rich, not that I'm trying to pick a fight or anything, but why would you say such a thing? Clearly cast pistons can handle the stresses involved so long as they are designed for that abuse, because OEM's have been doing it for years in turbo and blower cars.

I mean, I wouldn't put a bone-stock cast 350 SB Chevy piston in a 600hp blown nitrous car because that's silly, but if KB made a piston specifically engineered to handle that kind of stress, why wouldn't you use it? Especially if there might be advantages (weight/cost/clearance/etc.) to doing so? You see, this is exactly the kind of thinking I'm trying to question. I've received a ton of "you need to use forged," but when asked why, all I get is "well, I'd never use a cast piston." I'm sorry, but that's just not a sufficient answer.

KB's hypereutectic designs have been repeatedly run in nitrous, turbo, and blower cars with no abnormal failure rates. Lingenfelter's getting 550hp on stock LS1 internal cast pistons (although I wouldn't trust that in my car simply because I don't think GM designed that much of a safety margin into their pistons).

I guess the question boils down to this: it's not whether you would use a hypereutectic piston, it's whether or not you have used one (or know someone who did) and had bad results. Everything else is just old wives tales.

Understood. Your point is stated in an articulate way and I understand where you are coming from.

I am not saying I have any information beyond what may be a predjudice. Do I have any personal knowledge that what people like Lingenfelter, Vizard, Yunick, etc. have said (that "forged pistons are stronger") is true,. Nope. But I just don't have enough motors to be the one to verify what the limits of the available cast pistons are.

Possible benefits: less "piston slap" and oil consumption with a cold motor. Less costly (by a small amount given the cost of the whole project). Possible downside: piston life is drastically decreased. As I said, I don't want to be the one to "prove" it one way or another.

But it's a good question that I really can't answer because I have never tried it.

Rich

i dunno about the other cars, but the supra pistons are definetly cast, and ive seen quite a few make 800+rwhp on them.

i think the crank and rods are forged though.

FYI, I think most of the reasoning behind OEM cast pistons in FI applications is driven by emmissions concerns, less bore wear, and the fact that they are cheaper to produce. Also, there is a greater degree of freedom with designing cast pistons - some designs would be impossible to duplicate with a forged piston. Not sure if I can believe the "drastically reduced life" disadvantage - lots of high milage TR's and mopar turbo 2.2 still out there getting flogged on w/ lots of boost on a regular basis without a problem.

Strenght has always been an advantage of forged pistons, but I also think the strength advantage really doesn't make any difference for the majority of people out there... FWIW, I think the strength gap is getting narrower and narrower - Subaru is already claiming that their new cast hyper pistons in the STI are significantly stronger than the forged piston that were previously used.

Of course, you'll always have the guy who blows his stock LT1 up with a bad tune and 12psi on pump gas, and then blames it on the hyper pistons ;)

I guess the question is "How much extra are you willing to pay"?

I know there are plenty of "ultra-light" forged pistons that arn't rated for more than 400 hp or so... but likewise a heavier forged piston for the same company and alloy can handle 1000+ without a hic-up. The mess gets even more interesting when you consider that alloy purity and type can vary (either knowingly or not)... and then there's obviously the machining and forging process.

Lots of variables to look at... similar situation with hyperutetic pistons I imagine. A cast piston (regardless of silicon content), is still subject to casting flaws that might cause problems.

I'm not a big fan of spending money where it's not needed, but for a 500hp Vette, I think I'd be more conserned about the labor / time / money lost if there should ever be a problem. I know it sounds like a cop-out, but honestly, if you're building an engine yourself, this is closest thing you'll get to a warranty. Cheap insurance considering.

The "failure is a failure" theory doesn't float in my books... if it deforms and gouges a cylinder wall, fine... much better than throwing a chunk to hit a rod bolt rotating at 7000rmps. When the flywheel's next to my ankles I'd prefer the engine is designed to "wear" or "colapse"... not explode. :)

lol... I know it sounds dumb, but the cost difference just isn't enough to validate going with hyper-pistons in my mind. Not to mention the PITA it'll be to rebuild the shortblock with forged slugs should you deside to spray later. OEM's build generous allowances into engines to prevent rare situations from causing havok, I personally want to retain some of that buffer when rebuilding for more ponies.

Build shortblocks for 700, build top-ends for 500. :) (might sound like a dumb theory, but I honestly don't have the want or time to rebuild an engine everytime I install a new bolt-on, or find myself driving on a cold, dry day 2000 ft below sea level. (well, you get my point I guess).

I would be a fool to assume I could assemble an engine as perfectly balanced as Lingenfelter could after his decades of building/racing. For that reason, I'm being a cafeful and deliberate as possible. Hell, it took me 4 months to find the block I wanted (200 miles LT1), and another 4 to pick/locate/afford the pistons I need. Rods and a crank are next... :)

Oh yeah, and just for the record, we have plenty of hyper pistons running close to 500hp in the NW.

I can think of one LS1 putting down ~430rwhp (T56) with the stock pistons, and an LT1 putting down ~420rwhp (through an 4L60E) on the factory shortblock UNTOUCHED.

500 to the wheels is pushing it for sure... but 500 hp shouldn't be unobtainable with a purpose-built Keith Black slug. Just depends how much room you want for error (during tuning, racing, spraying, or otherwise).

Scottie-GNZ over at TurboBuicks.com has run 10.08 @ 136.44 with his Buick V6 powered 240Z @2800 pounds. He is making roughly 500HP on a 6 cylinder and drives alot of miles on the street as well. Not bad at all for "HyperJunk" pistons as he puts it.

People were always saying that his engine would never last, always saying that forged were the only answer other than stock cast turbo pistons. I think he's showing that the tune up is more the answer.

this is from KB web site


Hypereutectic -vs- Forged Pistons


Hypereutectic pistons are used in some original equipment engines. They are favored because of reduced scuffing, improved power, fuel economy and emissions.

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.

With this in mind, we caution the reader about the use of non-T6 heat treated O.E. design hypereutectic pistons for high performance. Silvolite and others do make replacement-type hypereutectic pistons that are worthwhile for stock replacement applications. Original equipment design is almost never suitable for performance applications.

The KB line of hypereutectic pistons were designed around the 390 alloy. The result is a high performance part intended to give the performance engine builder access to the latest in piston technology.

Forgings have long been the mainstay of the performance business and did well in the big cubic inch engines of the 60’s. Now, with focus on peak cylinder pressure timing, ring sealing dynamics, cylinder air tumble and swirl, combustion chamber science, and extended RPM ranges, we need to consider some new piston options.

The KB T6 hypereutectics are considerably different than the forgings. The KB pistons have shown improvement in power, fuel economy, cylinder sealing, service life, and cost effectiveness. The reduced thermal expansion rate allows the piston to be run with reduced clearance. A tight piston is less likely to rock, make noise, and burn oil. A rocking piston wears rings and increases blow-bye. The close fit of the KB piston allows the piston rings to truly seal, minimizing blow-by.

The design flexibility enjoyed by the KB series of pistons has an advantage over present day forging practices. The die for a forged piston must be designed so it can be easily removed. This limitation makes it difficult to make a light weight piston without sacrificing strength.

The KB pistons' utilization of the permanent mold with multiple die parts allows undercut areas above the pin hole and material distribution in the skirt area that stiffen the entire piston unit. The forged piston requires thick skirts to achieve comparable piston rigidity. A rigid piston rocks less in the cylinder and improves ring seal.

The forged pistons' thick skirts add weight. The design of KB pistons gives us the option to build the lightest pistons on the market.

Some current KB pistons are not super light for several reasons. If the piston is to be used as a stock replacement, more than a 10% weight reduction will mandate that the engine be re-balanced.

Common sense suggests that the introduction of a new product be extra strong at the initial release. As the product becomes accepted, weight reductions are scheduled as regular product upgrades, as justified with actual race testing.

There will always be a market for custom forged pistons. Small runs of forgings are more economical than small runs of permanent mold pistons because of the complexity of permanent mold tooling. Where quantities justify, expect to see future KB pistons developed that are lighter and stronger than anything else on the market. Machined head profiles are easily changed with our CNC equipment so we will stay current with new cylinder head developments. Volume production is expected to keep the price reasonable.

Our pricing policy has given the impression to some that we are building an economy, or in between, piston. The truth is, we are striving to build the "State of the Art" piston that is best, regardless of price. Reasonable pricing is just an added benefit.

Maldo beat me to it.

i can't say that i know anything for sure, but i'm impressed enough with the tech articles on KB's website that i'd be comfortable with letting them choose my pistons for me. i suggest you all take a look.

basically, if John Irb thinks it'll do, i'll take his word for it.

Originally posted by Steve in Seattle
I'm not a big fan of spending money where it's not needed, but for a 500hp Vette, I think I'd be more conserned about the labor / time / money lost if there should ever be a problem. I know it sounds like a cop-out, but honestly, if you're building an engine yourself, this is closest thing you'll get to a warranty. Cheap insurance considering.

If I were doing this for money reasons I would agree with you, but I'm not. If forged were the best way to go, I'd go with it regardless of cost. As you stated, considering the total motor costs, forged vs. cast doesn't change the cash that much. However, I'm looking at hyper pistons because they may offer advantages in less blowby and oil consumption. Or, you might say that I'm trying to not consider forged because of the disadvantage of requiring extra piston to wall clearance.

Someone already posted the contents of the KB piston website article on hyper pistons, and it lays out a great deal of the information on why I'm looking at them. Of course, I don't consider KB to be entirely -- ahem -- objective in this matter because they're one of the primary makers of hyper pistons. Just as I would expect them to suggest hyper pistons, I'd expect Speed-Pro, TRW, and so forth to suggest only forged pistons because that's what they're pushing. Only here can I get some (hopefully) objective responses to my question.

Originally posted by EddieP
Strenght has always been an advantage of forged pistons, but I also think the strength advantage really doesn't make any difference for the majority of people out there... FWIW, I think the strength gap is getting narrower and narrower - Subaru is already claiming that their new cast hyper pistons in the STI are significantly stronger than the forged piston that were previously used.

This is my thinking as well. I thought, which would be stronger? A purpose-built cast hyper piston, designed to handle 600hp turbo applications, or an off-the-shelf generic forged piston? Costs for the super-duper cast piston might well exceed the cost of a generic forged piston, so it's not cash savings I'm after. In a word, it's convenience. I don't want to be adding a quart of oil every 2000 miles, it's as simple as that.

Originally posted by prisoner881
Of course, I don't consider KB to be entirely -- ahem -- objective in this matter because they're one of the primary makers of hyper pistons. Just as I would expect them to suggest hyper pistons, I'd expect Speed-Pro, TRW, and so forth to suggest only forged pistons because that's what they're pushing. Only here can I get some (hopefully) objective responses to my question.

Actually, KB makes forged pistons also... just like Speed-Pro/TRW produce cast hyper pistons.

Originally posted by prisoner881
Rich, it has nothing to do with pinching pennies, trust me. I'm not willing to cut a dollar anywhere so long as that dollar's well spent. The goal of this project is to have a 500rwhp 'Vette that is just as reliable and maintenance-free as a stock 'Vette. I could probably get this with a normally-aspirated larger displacement motor and a radical cam, but I want this thing to be a smooth sleeper. No barking exhaust. No lopey cam. No piston slap. No sewing-machine-noisy valvetrain. And above all, no excessive oil consumption.



Soooo...the twin turboes whining and blow off valve arent signs of a beast under the hood?

Originally posted by jonaddis84
Soooo...the twin turboes whining and blow off valve arent signs of a beast under the hood?

Heh heh...I like the way you think.

However, you've touched on another reason why I'm going with turbos as opposed to just a regular centrifugal blower. You can hear a blower car idling a mile away, even with the "quiet" gears on some blowers. I've sat next to really radical turbo Buick GN's and, until they get on the loud pedal, you never hear the hair dryers. Sure, if somebody powerbrakes you'll hear 'em spooling up, but that's unavoidable. I just want a motor that idles smoothly, is as maintenance-free a stock engine, gets good gas mileage when I drive it sanely, but has gobs of Ford-eating horsepower under the hood when I ask for it. Oh, and I don't want to refill a bottle, either.

That has turbos written all over it. Besides, with me being the engineering type, I have a thing for mechanically elegant designs. Turbos are more efficient than blowers, and that appeals to me. Anyone can bolt on a blower, but turbo cars are a rare and special thing when it comes to V8 horsepower these days.

Originally posted by EddieP
Actually, KB makes forged pistons also... just like Speed-Pro/TRW produce cast hyper pistons.

Yeah, but KB's Silv-o-lite line is their premiere line, and I expect them to push them.

Originally posted by prisoner881
Heh heh...I like the way you think.

However, you've touched on another reason why I'm going with turbos as opposed to just a regular centrifugal blower. You can hear a blower car idling a mile away, even with the "quiet" gears on some blowers. I've sat next to really radical turbo Buick GN's and, until they get on the loud pedal, you never hear the hair dryers. Sure, if somebody powerbrakes you'll hear 'em spooling up, but that's unavoidable. I just want a motor that idles smoothly, is as maintenance-free a stock engine, gets good gas mileage when I drive it sanely, but has gobs of Ford-eating horsepower under the hood when I ask for it. Oh, and I don't want to refill a bottle, either.

That has turbos written all over it. Besides, with me being the engineering type, I have a thing for mechanically elegant designs. Turbos are more efficient than blowers, and that appeals to me. Anyone can bolt on a blower, but turbo cars are a rare and special thing when it comes to V8 horsepower these days.

Good points. I just thought it sounded funny at first, I understand though. Someday Id like a set (or maybe a single) or turboes blowin my LT1. Until then NA+N20 is all for me.

Another point that should be addressed. I just heard from a local engine builder round here that there are "two" different types of Forged pistons.

1. West coast
2. East coast

he said, for what reason I forget, that the East coast is a premier piston (wiseco, TRW, and one other). reason being is you can run a much tighter PTW clearance, I think he said almost .07" or maybe a little more than the "west coast" slugs. He spoke that the way to tell the difference is the color of the aluminum, the east coast are a much more dull gray than the more shiny west coast.

Anyone else heard this before?

Just putting this out there. I am in the boat with Damon.Kb hyper slugs in a flat top 355 solid roller motor. I turn it 7000 rpm on a 150 shot of go fast gas. Runs like a champ.

I was just yesterday taking a look at my new JE "blower/nitrous" pistons before bolting things together. The instruction sheet said something to the effect "these pistons are made from a 2618 aluminum alloy that contains no silicon" (maybe I am not getting the number right). Hmmm..........

Rich Krause

Originally posted by rskrause
I was just yesterday taking a look at my new JE "blower/nitrous" pistons before bolting things together. The instruction sheet said something to the effect "these pistons are made from a 2618 aluminum alloy that contains no silicon" (maybe I am not getting the number right). Hmmm..........

Rich Krause ...which means it'll wear like a mofo in a street car.:D

Originally posted by rskrause
I was just yesterday taking a look at my new JE "blower/nitrous" pistons before bolting things together. The instruction sheet said something to the effect "these pistons are made from a 2618 aluminum alloy that contains no silicon" (maybe I am not getting the number right). Hmmm..........

Rich Krause

Doesn't this sound like some sort of misprint? I'm no metallurgist, but I thought even forged components had some silicon in them.

See item #2 on the JE 2618 instruction page:

http://www.jepistons.com/pdf/piston_instrc2618.pdf

2. Your pistons are manufactured from 2618 non-silicon aluminum alloy.
On the other hand, if you look up the specs for 2618:
Chemistry Data :

Aluminum: Balance
Copper: 1.9 - 2.7
Iron: 0.9 - 1.3
Magnesium: 1.3 - 1.8
Nickel: 0.9 - 1.2
Remainder: Each 0.05 max
Remainder: Total 0.15 max
Silicon: 0.25 max
Titanium: 0.04 - 0.1

Nice hotrod Fred.... :-) Very nice.

back to the regular broadcast.

my views of pistons

hyper pistions are like the super model with std you know you want to put it in her but your affraid of the consequences.

forged pistions- the only reason why i like them is the tend to hold together better un like hyper that tend blast your engine with metal particals when they go.
hyper is not all that bad but I rather pay the few extra dollars, have a little extra weight (couple grams big whoop) and know i have a quailty part. Also when things go bad it keeps engine damage to a minium. But if you really want to hyper will work, but forged is good insurance.

overall I would not put any thing in my engine that im not 100% confidence Im I have a doubt or have a question of liabilty like your asking that part is not coming close to my engine bay.
If in doubt throw that sh!t out.

My personal and mostly unscientific rule of thumb is that anything above 1hp per cubic inch gets forged pistons.

Originally posted by LameRandomName
My personal and mostly unscientific rule of thumb is that anything above 1hp per cubic inch gets forged pistons.

Production LS6 (Z06/CTS-V) makes do with cast hypers @ 1.16-1.17 hp/cube. You ARE a conservative fellow. :)

SSTroker, what would you say is a practical upper limit for hypers? I have a 355 with hypers that would see nearly 575hp and 6,500rpm with a little bit of nitrous. I also have stock crank and rods, though it's balanced and with arp bolts. I'm afraid to spray the thing because I have a buyer for it as long as it's running:D

Originally posted by nosfed
SSTroker, what would you say is a practical upper limit for hypers? I have a 355 with hypers that would see nearly 575hp and 6,500rpm with a little bit of nitrous. I also have stock crank and rods, though it's balanced and with arp bolts. I'm afraid to spray the thing because I have a buyer for it as long as it's running:D

I'm not a fan of using nitrous with hyper-pistons, although plenty of people do. I'd probably get into the high 400's (flywheel) without spray on hypers with my own engine. I'm conservative (but maybe not as conservative as LRN), so if I thought I'd get over 500, I'd probably go forged.

I really like your idea of not spraying with a buyer in your back pocket. :)

I've turned the KB hypers to 7300 rpm with a dual stage (200hp) nitrous system on an older bracket car. Kb hypers, Scat I-beams, C&A taper wristpins, plasma moly rings.....
Goes without saying that the a/f mixture needs to be fat, but I never had any problems out of this motor until a broken lifter took it out.

Yeah, I'd try to keep it together if you're planning to sell and play with something else if you want to push things.;)

-Mindgame

Originally posted by OldSStroker
Production LS6 (Z06/CTS-V) makes do with cast hypers @ 1.16-1.17 hp/cube. You ARE a conservative fellow. :)


Guilty as charged. :D

Anyone know the difference between JE and SRP forged pistons. Say you were to buy the same exact piston from both, say a nitrous/blower piston, 16cc dish, yada yada yada....they are made by the same company, both forged aluminum pistons. What makes the JE ~$200 or whatever it is more expensive?

Originally posted by OldSStroker
Production LS6 (Z06/CTS-V) makes do with cast hypers @ 1.16-1.17 hp/cube. You ARE a conservative fellow. :)

Actually, the 2.4 turbo from DCX and the LS6 from GM both use a Mahle 142 alloy, which is eutectic. The 2.4 turbo has piston cooling jets though, which makes a huge difference to piston life. The 142 alloy pistons in these applications are cast, but the silicon content is lower than hypereutectic pistons. This makes the pistons more forgiving and less brittle. I'm doing a NA engine right now using Mahle's 124 alloy with piston cooling jets. The jets can easily reduce the piston crown temp by 20-30 deg. C.

Mahle has 2 alloys they generally use in the US - 124 and 142. They both are eutectic alloys, but the 142 has a higher copper content to help it's fatigue resistance in the higher temperature ranges, above 200 deg. C or so. The extra copper makes the piston heavier though. Since we are really going after mass on the engine we stayed with 124 and added cooling jets. Karl Schmidt has similar alloys to Mahle, and also does not use hypereutectic pistons. Ford uses a lot of KS pistons. Federal-Mogul has 413 and 425 alloys. 413 is just about dead in their line. Last I heard the GM 3.8L engine was the last one to use it. 413 is a eutectic alloy. 425 is used in all other US sourced pistons by Federal-Mogul. It's a hypereutectic alloy. Hypereutectic alloys got their start in the US to help eliminate top ring groove wear and microwelding. It's a whole lot cheaper than anodizing if your application has borderline microwelding or ring groove wear issues. The wear ratings I've seen from a hypereutectic piston vs. a eutectic seem to indicate a 10% reduction in wear with hypereutectic, which can make a difference over a long durability test if you have marginal top ring groove life.

I can tell you the new 500 HP 7 liter LS7 will be using 142 Mahle pistons, cast, unless things change before launch. I can also tell you a very high output supercharged Northstar engine should be coming to market soon with a 425 alloy F-M piston. You can use any good alloy for a piston design. You just have to make sure you design for the intended application. The problem with many aftermarket designs in this respect is they were almost certainly not designed for your specific application. As such, I'd tend to buy components that seem to be way overdesigned for my application, just in case.

Thanks for the correction.

Aren't most high(er) performance aftermarket pistons for US V8's either cast hypereutectic or forged? Mahle's Power Pak are forged 4032 or forged M138. Even if Mahle offered 124 cast as an economical high perf piston, the market would probably go for the forged 4032.

An NA engine with oil cooled pistons? Sounds "trucky" to me. Will it be constant cooling or load sensitive? If I recall, Lycoming aircraft engines only sprayed oil during boost conditions. That may not be true, however. I forget easily.

I don't know for sure about aftermarket pistons. There are so many different alloys it's hard to keep up. Since I haven't started building my engine yet I haven't really tried to do the research. That's one of the reasons I'm reading this board.

The Hemi engine has very hot pistons and quite high EGTs from the factory. Since our engine is higher output than the current Hemi we were concerned, so we added piston cooling jets from the beginning. It's lucky we did. We did a test plugging the squirters running 300 deg. F oil recently and promptly destroyed a piston. We didn't have the knock sensors active so hot spots did us in.

The squirters are pressure activated. IIRC, they come on at 25 psi. That may be raised soon depending on oil consumption testing results.

You guys have some interesting threads on this board. I'm home sick today and can't seem to sleep so I'm spending some time perusing the board.