Forged vs. Hypereutectic for turbo applications
03-23-2004, 04:07 PM
#1
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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?
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?
03-23-2004, 05:06 PM
#2
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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
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
03-23-2004, 05:14 PM
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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?
==========================================
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
==========================================
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
03-23-2004, 07:08 PM
#4
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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 Krause
03-23-2004, 08:10 PM
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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.
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.
03-24-2004, 02:02 PM
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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
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
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.
03-24-2004, 03:15 PM
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Originally posted by EddieP
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.
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.
Rich
03-24-2004, 04:08 PM
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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
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
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.
Last edited by prisoner881; 03-24-2004 at 04:11 PM.
03-24-2004, 04:18 PM
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Originally posted by rskrause
I think my info must be out of date then?? I still wouldn't use cast psitons though.
Rich
I think my info must be out of date then?? I still wouldn't use cast psitons though.
Rich
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.
03-24-2004, 06:19 PM
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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.
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.
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
03-24-2004, 08:35 PM
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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
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
03-24-2004, 09:44 PM
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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...
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...
03-24-2004, 09:48 PM
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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).
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).
03-25-2004, 06:07 AM
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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.
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.