LS7...not so good

I've been hearing that alot of the LS7's have been breaking pistons.:eek: I Hope they figure out whats going wrong. :mad:

Sorce: Corvette Masters, Orlando FL

It is probably some Ford GT owners posting that. :D I havent heard anything

What's the definition of "a lot" ? Any actual numbers?

ok I sure as hell dont have a dam Ford.... and no i dont have any numbers.... it was just some shop talk, from a very reputable guy. their shop is fantastic if any central Fl people are looking to have some work done.

Well there can't be that many Z06's out on the streets yet, so its important to know what they/you mean by "a lot". 2 cars? 3 cars?

I'll be back at the shop next week and ill ask.

Heh.. If you are going ot make a statement like that, you gotta back it up with data...

Well there can't be that many Z06's out on the streets yet, so its important to know what they/you mean by "a lot". 2 cars? 3 cars?
Its funny how two or three cases becomes grossly exaggerated to 2 to 3 thousand.

This could just be an isolated case even if its true. No point in jumping to conclusion without solid numbers.

I frequent the digital corvette forums and haven't seen or heard anything about any engine problems with the new Z06's. In fact I haven't heard about any problems period :shrug:

I wouldn't have a clue... but aren't the pistons similar in design/manufacture to the C5R racers?

well...that one guy blew his motor because he was spraying with platinum plugs...

well...that one guy blew his motor because he was spraying with platinum plugs...

Spraying a new $70k++ car while under warranty.....no wonder GM can be so hard on claims....:rolleyes:

If you are going ot make a statement like that, you gotta back it up with data...Agreed - regardless the brand of car.

well...that one guy blew his motor because he was spraying with platinum plugs...

Sprayin with platnium plugs , and those lightweight cast aluminum pistons :lol: The pistons are about the only weak link in the LS7 , when nitrous comes into the picture . I bet you do see more than few scenarios like this with the new Z06 and nitrous . Given its bulletproof assembly I could easily see a few less knowledgeable or plain stupid people overlooking the cast pistons . No fault of GM whatsoever .

I have heard about guys finding very abnormal amounts of metal shavings in the oil on many of these new LS7s. Haven't heard about any blowing pistons though. Don't know how many guys this has affected either, so I wouldn't go calling the motors pieces of crap yet. I would still not be adverse to having an LS7 show up in a 5th gen.

The LS7 pistons are really cast?

Of all the things to pinch a dollar on GM.....

Yeah, they are cast, but that doesn't make them horrible yet. Let more guys get the cars/engine first, and then we will start seeing more torture tests done to them. Forged are good, but hypereutectic don't automatically mean garbage.

Cast pistons dont have silicone in them. Hypereutectics do. So what do they have??

(and yes, I know that hypers are cast aluminum)

Cast pistons dont have silicone in them. Hypereutectics do. So what do they have??

(and yes, I know that hypers are cast aluminum)

They are cast hypereutectic. When was the last a cast aluminum piston used in an automobile engine? I would imagine it has been a LONG time, since I believe pure aluminum melts at around 1220 degrees Farhenheit, and gets soft much earlier than that.

i thought hypereutectic was better for spray, and forged was better for boost?

The reason they use Hyper pistons, the same in every LT1/4 and all the LS motors, is bcuz they are lighter then forged pistons.

sounds like someone opened a can of woop ass on the asphault... either that or a can of woop ass on an LS7...

I mean these guys running around with headers and stuff arent complaining...

i'm sure though if you put some forced induction you might run into some problems...

or some juice... spray a little here, a little there, a little all the way down to the fair...

They are cast hypereutectic. When was the last a cast aluminum piston used in an automobile engine? I would imagine it has been a LONG time, since I believe pure aluminum melts at around 1220 degrees Farhenheit, and gets soft much earlier than that.

Hypereutectic can withstand more heat then most pistons... but... but... they cant handle high pressures caused by forced induction...

Ok, if GM gives me a LS7 for free, I'll make sure to do an extensive field test by dropping it into my truck and give the the results to dispell these nasty rumours :D

The reason they use Hyper pistons, the same in every LT1/4 and all the LS motors, is bcuz they are lighter then forged pistons.

Cast (regardless of post-processing and metallurgy in the case of common piston materials) is less expensive than forged.

Now, the guy that sprayed the car and blew up his motor got what he deserved, and in no way is GM responsible...

BUT...

... all in all I think the inclusion of hyper-u-explode-it pistons in the LS7 is major failing on the part of Powertrain. There will be all kinds of reasons one way or another, and certainly trade-offs (expansion and noise come to mind...), but the overriding goal for the LS7 MUST BE a bullet-proof short block. Forged pistons are the way to remove a possible weak link.

I doubt the use of hyperutechtic (sp?) pistons was a cost move as much as knowing that forged piston have more cold piston slap...and lord knows they already warranty enough LS* motors for that.

Add to the fact that they use low tension rings and close tolerances, and forged would have had the rich Corvette (not hardcore) owners crying in their wine glasses.

I doubt the use of hyperutechtic (sp?) pistons was a cost move as much as knowing that forged piston have more cold piston slap...and lord knows they already warranty enough LS* motors for that.

Add to the fact that they use low tension rings and close tolerances, and forged would have had the rich Corvette (not hardcore) owners crying in their wine glasses.

Doug: The following is not a critque of you, but I'm going to use strong language that may appear to have a tone nastier than I mean it.

Unacceptable. Cast pistons in a motor of this stature are unacceptable.

Beg, borrow, steal... or better yet... put some razor-sharp engineering minds on it and come up with a forged piston that doesn't make noise or addresses the issue some other way.

Forced induction motors use forged pistons all the time. It can be done, and should be done.

Pistons are no place to go cheap, and no place to accept a compromise in robustness on a motor installed in a $70,000 car. If you have to add some $$$$ to the price of the car to get them, so be it.

Not saying there haven't been any LS7 failures but to open a topic with the words "LS7 not so good" has broad negative implications. Thus needs to be backed up with more than shop talk.

Not demeaning or discrediting the original poster, just my opinion if your gonna salvo a molotov cocktail into a crowd of excited people, the expected reaction should be anticipated, thus you better come prepared with more than a pair of nail clippers as backup. :D

This sort of shop talk reminds me of people that still to this day tell me GM is having a terrible problem with the Duramax diesel aluminum heads melting, oooohhhhh lordy, I just turn and walk away, it's not worth it.

Doug: The following is not a critque of you, but I'm going to use strong language that may appear to have a tone nastier than I mean it.

Unacceptable. Cast pistons in a motor of this stature are unacceptable.

Beg, borrow, steal... or better yet... put some razor-sharp engineering minds on it and come up with a forged piston that doesn't make noise or addresses the issue some other way.

Forced induction motors use forged pistons all the time. It can be done, and should be done.

Pistons are no place to go cheap, and no place to accept a compromise in robustness on a motor installed in a $70,000 car. If you have to add some $$$$ to the price of the car to get them, so be it.


Dan,

No offense taken ;)

And I agree, I'd MUCH rather have forged pistons whatever the tradeoff in noise.......especially in this kind of motor.

Not saying there haven't been any LS7 failures but to open a topic with the words "LS7 not so good" has broad negative implications. Thus needs to be backed up with more than shop talk.

Not demeaning or discrediting the original poster, just my opinion if your gonna salvo a molotov cocktail into a crowd of excited people, the expected reaction should be anticipated, thus you better come prepared with more than a pair of nail clippers as backup. :D

This sort of shop talk reminds me of people that still to this day tell me GM is having a terrible problem with the Duramax diesel aluminum heads melting, oooohhhhh lordy, I just turn and walk away, it's not worth it.

I think that at the center of all shop talk is an element of truth. I group this LS7 piston failure in with Camaro's glass axles. Parts perfectly fine for normal stock use, but as soon as you tweak with things they let you know where costs were cut. Not a fair way to judge, but any weakness tends to take on a life of it's own.

The LS1 is a perfectly good engine. But the racket and piston slap the one in my B4C (and other Camaros I ridden in) gives me the feeling it's a far inferior engine than the LT1 in my old Z. Even though it has far more horses, and perhaps have more up to date engineering, I'm often fighting the urge to replace it with an older LT1 Z.\

Impressions count at least as much as reality.

guion,
Didn't your '97 have piston slap? God knows mine does...I asked about it on this website the morning after I bought it. I had never experienced piston slap before, and man...is it disconcerting. My car, when stone cold, sounds like crap over 2,500. Within 15-20 seconds, it smooths right out at any RPM (I always wait until it reaches operating temp to yank on it, though).

I thought LT1s were as bad as LS1s with that?

In the red corner we have:

And I agree, I'd MUCH rather have forged pistons
whatever the tradeoff in noise.......especially in this kind of motor.

And in the blue corner, we have:

The LS1 is a perfectly good engine. But the racket and piston slap the one in my B4C (and other Camaros I ridden in) gives me the feeling it's a far inferior engine than the LT1 in my old Z.

And we regret to announce that our regularly scheduled referee for this evening's event, General Motors, who was battling a bad case of "DamnedIfYouDoDamnedIfYouDont" disease, was pronounced dead just awhile ago. But on that note:

LLLLLLLLLLET's GET READY TO RUMBLLLLLLLLLLLLLE!!!

"The LS7 doesn't have forged pistons? What a piece of crap!"
"The LS7 has piston slap just like that crappy LS1? What a piece of crap!"
"I can't buy an LS7 without selling a kidney? What a piece of crap!"
"The LS7 won't make my hair grow back? What a piece of crap!"

Where will it end....

guion,
Didn't your '97 have piston slap? God knows mine does...I asked about it on this website the morning after I bought it. I had never experienced piston slap before, and man...is it disconcerting. My car, when stone cold, sounds like crap over 2,500. Within 15-20 seconds, it smooths right out at any RPM (I always wait until it reaches operating temp to yank on it, though).

I thought LT1s were as bad as LS1s with that?

Never had an issue with my LT1 up to the day I sold it at 166,000 miles.

There was a small manifold vacuum leak that was developing towards the rear. But unlike my LS1, the engine used no oil, had no piston slap, and didn't make any unseemly noises.

Maybe I got one of the good ones, because outside of higher revving performance, that LT1 ran circles around my LS1 in perceptions of being a good engine. Too bad the clutch and rear end weren't made as well.

In the red corner we have:



And in the blue corner, we have:



And we regret to announce that our regularly scheduled referee for this evening's event, General Motors, who was battling a bad case of "DamnedIfYouDoDamnedIfYouDont" disease, was pronounced dead just awhile ago. But on that note:

LLLLLLLLLLET's GET READY TO RUMBLLLLLLLLLLLLLE!!!

"The LS7 doesn't have forged pistons? What a piece of crap!"
"The LS7 has piston slap just like that crappy LS1? What a piece of crap!"
"I can't buy an LS7 without selling a kidney? What a piece of crap!"
"The LS7 won't make my hair grow back? What a piece of crap!"

Where will it end....

Doug stated that he'd rather have forged pistons, and I would too. Sorry no battle here. I simply stated that my LT1 didn't have the piston slap my LS1 does. :lol:

My 5.0 Mustangs had forged, my Thunderbird SC has forged, I don't see why a $70,000 car shouldn't have them as well.

hyper crap pistons don't take to nitrous or blowers at all.
They have no tolerance for detonation.
I'd take old school cast pistons before I ever sprayed a hyper crap piston.
Now combine that with the already high compression which means a lot of people who spray the ls7 will probably get a little detonation which in turn will break pistons all the time if they are indeed hypercrap.

Luckily you can replace them with low compression forged pieces and fix both problems at once before throwing on a blower.

Who cares? Seriously, how many Z06 owners are going to throw nitrous or FI onto their LS7?

I don't care if you're buddy's friend's cousin is doing it, fact is only a small percentile will mod them and a small percentile of those people will have detremental issues with the engine.

"The LS7 doesn't have forged pistons? What a piece of crap!"
"The LS7 has piston slap just like that crappy LS1? What a piece of crap!"
"I can't buy an LS7 without selling a kidney? What a piece of crap!"
"The LS7 won't make my hair grow back? What a piece of crap!"

Where will it end....

Where it should end, in the engineering department.

"Mr. BSME, your job from here on out is to make our LS7 pistons absolutely bulletproof. They cannot make noise, they cannot cause detonation problems, they cannot cause oil consumption problems, they cannot cause other problems, and they must be so robust that a piston failure is a quantity unknown on the LS7 for the rest of the life of the engine program. We will pay a premium for pistons of this type because it simply makes sense to. Should you fail, you will be taken out back and unceremoniously shot dead on the spot and then dropped into the Detroit River."

No excuses. No bu!!sh!t. Assign the responsibility, accept the cost, empower the engineer and GET IT DONE.

But Danno'.....aren't you the one who also says that major battles are fought over even the smallest of cost increases?

(I'm just playing devil's advocate with you ;) ...I like to see you go off!! :lol: )

Hypereutectic can withstand more heat then most pistons... but... but... they cant handle high pressures caused by forced induction...

I am aware of that. Most pistons have some degree of silicone in them nowadays, making them all eutectic to some degree. Forged pistons deal with the heat better as pressure. What does high pressure go hand and hand with? Heat

I think that at the center of all shop talk is an element of truth. I group this LS7 piston failure in with Camaro's glass axles. Parts perfectly fine for normal stock use, but as soon as you tweak with things they let you know where costs were cut.


Heh, my glass rear end is showing signs of crapping out on me soon, and I have never launched the car on sticky meat once.

I don't think cost had much to do with piston selection, if at all. The engine has lots of exotic parts that are not cheap, and I don't think they skimped here. There are many benefits to the Hypereutectic piston but if you look at the design of the engine, WEIGHT was probably the #1 factor in the decision. They are considerably lighter than a forged piston would be. Can anyone think why that might be important on a 427 cubic inch engine that spins to 7K? Those are very large pistons to sling around at that rpm...

Doug stated that he'd rather have forged pistons, and I would too. Sorry no battle here. I simply stated that my LT1 didn't have the piston slap my LS1 does. :lol:

My 5.0 Mustangs had forged, my Thunderbird SC has forged, I don't see why a $70,000 car shouldn't have them as well.

Impressions count at least as much as reality.

Forged pistons are noisier than hypereutectic. I'm sorry, it's just reality. Yet you said yourself that the piston slap in your LS1 left you with the impression that it was an "inferior" engine to your LT1. Do you honestly think that GM didn't take this into account when they built the LS7? Does it make sense that they would utilize a piston who's level of noise production could be mistakenly perceived as being the same condition found in the LS1, and therefore risk the impression of it being an "inferior" engine? Read between the lines.

Lemme break this down even further. If you had to choose between two "bad impressions" that the car you're building would go down in history as being known for, which would it be:

-Couldn't run NOS without changing the pistons

or

-A $70,000 Corvette with an engine that sounds like it came out of a $25,000
Camaro

:thumb:

I think that at the center of all shop talk is an element of truth. I group this LS7 piston failure in with Camaro's glass axles. Parts perfectly fine for normal stock use, but as soon as you tweak with things they let you know where costs were cut. Not a fair way to judge, but any weakness tends to take on a life of it's own.

Impressions count at least as much as reality.
*cough*supra*cough*
Maybe the hi-po z28 will be built like a rock since Red knows what hi-po drivers want.

Hmmm, thats sort of interesting. Would you guys rather a quicker engine, or a slower engine that is very sensitive to mods?

edit: :think:

The deal with the forged pistons is that cast pistons (hypereutectic or not) have an offset pin bore to minimise noise on cold startup. That's why they have a dot on top to indicate the front of the motor. Forged pistons can be put in either way as long as the valve reliefs are symmetrical.

The "piston slap" we speak of in this thread has notihng to do with that. Chevy is just a lil inconsistent with its finish hone and there is just a fuzz too much cyl wall clearance until the piston gets a lil heat in it and expands a fuzz. No biggie actually.

I've met probably no less than 20 GM vehicle owners that hear a little lifter chatter and say that its piston slap. When they just really need to change their oil filter more frequently, lol. Some fools even hear the "click" of the injectors and think something is "ticking" inside the motor. lol

Its also my understanding that a forged piston can make life hard on a knock sensor too but i dunno...

There are many benefits to the Hypereutectic piston but if you look at the design of the engine, WEIGHT was probably the #1 factor in the decision. They are considerably lighter than a forged piston would be. Can anyone think why that might be important on a 427 cubic inch engine that spins to 7K?

But...but...our cousin Darryl heard from his brother Darryl who heard from his other brother Darryl that them dag'gone hyper-YOO-tactics ain't good fer nothin' but ashtrays and spitoons!

You'da thunk them thar' city slicker college boy injuneers coulda dun figgered that out by now if they wern't so bizzy playin' with them fancy tella-scope-thinga-majiggers and buildin' motors like cousin Darryl does! Knowhutimean? ;)

Nah, we buy them from that Damned Yankee down the road who is always so expensive and says g**-damn all the time....

:p

The deal with the forged pistons is that cast pistons (hypereutectic or not) have an offset pin bore to minimise noise on cold startup. That's why they have a dot on top to indicate the front of the motor. Forged pistons can be put in either way as long as the valve reliefs are symmetrical.

The "piston slap" we speak of in this thread has notihng to do with that. Chevy is just a lil inconsistent with its finish hone and there is just a fuzz too much cyl wall clearance until the piston gets a lil heat in it and expands a fuzz. No biggie actually.

I've met probably no less than 20 GM vehicle owners that hear a little lifter chatter and say that its piston slap. When they just really need to change their oil filter more frequently, lol. Some fools even hear the "click" of the injectors and think something is "ticking" inside the motor. lol

Its also my understanding that a forged piston can make life hard on a knock sensor too but i dunno...


I have piston slap constantly, it just goes away some when the engine is warmed. It is still there though, it isn't that hard to hear. This is something GM knows about, and I am sure they are trying their damnedest to make sure their $70,000 car makes no engine noise whatsoever, cold startup or otherwise. I don't know if this is the reason why their are cast pistons running in the LS7, but I wouldn't put it past GM, given how notorious these engines are for making noise.

I don't think cost had much to do with piston selection, if at all. The engine has lots of exotic parts that are not cheap, and I don't think they skimped here. There are many benefits to the Hypereutectic piston but if you look at the design of the engine, WEIGHT was probably the #1 factor in the decision. They are considerably lighter than a forged piston would be. Can anyone think why that might be important on a 427 cubic inch engine that spins to 7K? Those are very large pistons to sling around at that rpm...
EXACTLY!

Also, how would you protect such a exspensive roatating assembly from stupid people and wanting warrenty work on the motor after it blows?

But, I have to say that the weight thing probably had more to do with the decision. Kind of funny, I'm sure if this was in a BMW people would think it would have been a fluke, but IF this is true, then it is just another piece of cramp from GM.

EXACTLY!

Also, how would you protect such a exspensive roatating assembly from stupid people and wanting warrenty work on the motor after it blows?

But, I have to say that the weight thing probably had more to do with the decision. Kind of funny, I'm sure if this was in a BMW people would think it would have been a fluke, but IF this is true, then it is just another piece of cramp from GM.

Why exactly are you asserting that a forged piston has to be heavier than a cast one?

The specific density of the materials is close, and as long as the cast part has no voids (which have a good chance of causing catastrophic failure and are a problem the forging simply doesn't have), the difference in density is offset by the fact that the forged piston can be designed with thinner walls due to it's inherently higher yield and ultimate tensile strength.

I'm not buying without better information, so please support your position with some data or other evidence.

Here's a little blurb from a performance company on the issue:

"There are disadvantages (to cast pistons) also, of course. The piston will be weaker in structure. It is often heavier since the manufacturer has to increase wall thickness in order to achieve sufficient strength. The heat expansion cannot be controlled and is therefore often not completely round since the piston pin requires some material on the inside. They are also produced in bulk with most manufacturers only producing sizes that are close to factory specifications. This also makes them more affordable."

This whole thing is more than likey more rumors than facts

Why exactly are you asserting that a forged piston has to be heavier than a cast one?

The specific density of the materials is close, and as long as the cast part has no voids (which have a good chance of causing catastrophic failure and are a problem the forging simply doesn't have), the difference in density is offset by the fact that the forged piston can be designed with thinner walls due to it's inherently higher yield and ultimate tensile strength.

I'm not buying without better information, so please support your position with some data or other evidence.

Here's a little blurb from a performance company on the issue:

"There are disadvantages (to cast pistons) also, of course. The piston will be weaker in structure. It is often heavier since the manufacturer has to increase wall thickness in order to achieve sufficient strength. The heat expansion cannot be controlled and is therefore often not completely round since the piston pin requires some material on the inside. They are also produced in bulk with most manufacturers only producing sizes that are close to factory specifications. This also makes them more affordable."


Hypereutectic alloys are also slightly lighter (about 2 percent) than standard alloys. But the castings are often made thinner because the alloy is stronger, resulting in a net reduction of up to 10 percent in the piston’s total weight.

Read that and more here http://www.aa1car.com/library/2003/eb40354.htm

Remember we aren't talking about standard cast pistons vs forged, we're talking about hypereutectic pistons which contain at least 12.5% silicon for additional strength, less weight, better expansion/contraction properties which allows tighter tolerances for less noise, less blow-bye etc.

This whole thing is more than likey more rumors than facts

Given anyone who buys Z06 C6 would be an absolute enthusiast, I think owners of such vehicles would regularly contribute to reputable boards such as this one if they ran into a few technical problems with engines.

In other words, such information would come across as first hand... not innuendo.

Forged pistons are noisier than hypereutectic. I'm sorry, it's just reality. Yet you said yourself that the piston slap in your LS1 left you with the impression that it was an "inferior" engine to your LT1. Do you honestly think that GM didn't take this into account when they built the LS7? Does it make sense that they would utilize a piston who's level of noise production could be mistakenly perceived as being the same condition found in the LS1, and therefore risk the impression of it being an "inferior" engine? Read between the lines.

Lemme break this down even further. If you had to choose between two "bad impressions" that the car you're building would go down in history as being known for, which would it be:

-Couldn't run NOS without changing the pistons

or

-A $70,000 Corvette with an engine that sounds like it came out of a $25,000
Camaro

:thumb:

Don't really give a hoot about NOS (to me it's lame, lowdown cheating anyway). But a high performance engine in an expensive car should IMO have parts that would make it bulletproof.

Noise was never a problem in my 5.0s, Ford's Mustang Cobras seem to have been able to make forged pistons that don't clank when cold, and my SC (outside of slight supercharger whine and Ford's typical noisy power steering pump) doesn't make a racket, so I don't buy theForged Pistons=Piston Slap school of thought.

Frankly, I know I'll never buy this Corvette or it's engine, even if I had the money (I feel the regular Corvette at 45K is a superior bargain to a $70K one....is it worth $25K over a regular Vette?! :no: ), so on a practical basis, the LS7 pistons could be made of glass for all that affects me. :lol:

I'd sell my left nut for an LS7!!!

Frankly, I know I'll never buy this Corvette or it's engine, even if I had the money (I feel the regular Corvette at 45K is a superior bargain to a $70K one....is it worth $25K over a regular Vette?! :no: ),
But the Z06 badges alone are worth $15,000.

I'd sell my left nut for an LS7!!!

Right Nut " WTF is so special about the left nut? Why aren't we ever pimped out for something special?"

Read that and more here http://www.aa1car.com/library/2003/eb40354.htm

Remember we aren't talking about standard cast pistons vs forged, we're talking about hypereutectic pistons which contain at least 12.5% silicon for additional strength, less weight, better expansion/contraction properties which allows tighter tolerances for less noise, less blow-bye etc.

Wait a second here, your example is flat-out wrong.

The example above from the article is addressing cast hypereutectic vs. cast eutectic, and doesn't address forgings at all.

A hypereutectic cast piston is decidedly inferior to a forged piston of suitable material from a strength standpoint. Casting does not provide the grain control of forging, regardless of alloy.

Wait a second here, your example is flat-out wrong.

The example above from the article is addressing cast hypereutectic vs. cast eutectic, and doesn't address forgings at all.

A hypereutectic cast piston is decidedly inferior to a forged piston of suitable material from a strength standpoint. Casting does not provide the grain control of forging, regardless of alloy.

From a strength stand point, there is no question as to the superiority of the forged piston. However there is a weight penalty. That article was to address your point that the cast piston would require reinforcement that would make it heavier than a forged one. Perhaps that would be true if you were trying to make a cast piston with the exact same strength as a forged one. The benefit of a hyperuetectic is that it is stronger than a regular cast piston, yet lighter than a forged one. That seems about right for this application. I don't think a naturally aspirated LS7 that is not detonated will have a problem. If you run it way lean, you may have a problem. The factory tune will not allow this. But undoubtedly some of us that like to mod our cars will make mistakes like poor aftermarket tunes or poorly designed/underfueled forced induction and nitrous systems. That's our fault, not a design flaw of the car. So in conclusion I think they had to decide whether to go with a lighter piston that can't take as much blatent abuse vesus a heavier one that would have forced them to to lower the max rpm to protect the assembly, and miss out on some hp because of it. The slower revs and extra stress on the crank isn't worth it when the hyper is strong enough unless severely abused. Anything could be stronger. A lead parachute would never tear, but I think the benefit is outweighed by the penalty.

More on the subject that speaks directly to cast vs forged. http://www.glmmarine.com/castvsforged.html

The major disadvantages to forged pistons are actually a result of the forging process itself. Forging results in a piston that is considerably heavier, than cast pistons, and is limited in the aluminum alloys that can be used to produce the piston. Additionally, the forging process also limits the design configuration of the piston itself.

Cast (regardless of post-processing and metallurgy in the case of common piston materials) is less expensive than forged.

Now, the guy that sprayed the car and blew up his motor got what he deserved, and in no way is GM responsible...

BUT...

... all in all I think the inclusion of hyper-u-explode-it pistons in the LS7 is major failing on the part of Powertrain. There will be all kinds of reasons one way or another, and certainly trade-offs (expansion and noise come to mind...), but the overriding goal for the LS7 MUST BE a bullet-proof short block. Forged pistons are the way to remove a possible weak link.

Bulletproof is not a synonymous term for idiot proof..

Nothing at all "wrong" with the LS7. If you haven't driven a car with the new LS7... which I have... then allow a little room for doubt about "issies" in this foolishness.

From a strength stand point, there is no question as to the superiority of the forged piston. However there is a weight penalty. That article was to address your point that the cast piston would require reinforcement that would make it heavier than a forged one. Perhaps that would be true if you were trying to make a cast piston with the exact same strength as a forged one. The benefit of a hyperuetectic is that it is stronger than a regular cast piston, yet lighter than a forged one. That seems about right for this application. I don't think a naturally aspirated LS7 that is not detonated will have a problem. If you run it way lean, you may have a problem. The factory tune will not allow this. But undoubtedly some of us that like to mod our cars will make mistakes like poor aftermarket tunes or poorly designed/underfueled forced induction and nitrous systems. That's our fault, not a design flaw of the car. So in conclusion I think they had to decide whether to go with a lighter piston that can't take as much blatent abuse vesus a heavier one that would have forced them to to lower the max rpm to protect the assembly, and miss out on some hp because of it. The slower revs and extra stress on the crank isn't worth it when the hyper is strong enough unless severely abused. Anything could be stronger. A lead parachute would never tear, but I think the benefit is outweighed by the penalty.

More on the subject that speaks directly to cast vs forged. http://www.glmmarine.com/castvsforged.html

Many people that wish for an all out racing engine don't really understand what goes along with an all out race engine. Light pistons allow rev possibilities that heavy pistons do not.

Nothing wrong at all with high silicone short skirted pistons. Spraying a motor not buit in all aspects for Nitrous is a mistake. Going forced on induction is a mistake on a motor not built for it.



Good job on pointing out what should be obvious.:bow:

One other thing to think about. Since the LS7 uses titatium rods(very light), would you want a piston that is heavier on the end of it or something more along the same weight?

I'm guessing that hypers and their tight fit were almost a requirement to meet cold-start emissions. 2006 regs are a lot tighter than 5.0 days.

EDIT- on the matter at hand, there always seemed to be a guy or two at Corvette Masters that spread some mildly outrageous rumor, to make you think he's "in the know." I always took it as "whatever." Robbie was always straight with me, though- gave me some good info on piecing an AC system together for my car (years and years ago).

I don't know what L98, LTx, or LSx motors spec is for piston side clearence, but the 5.0 motors with forged pistons were .02 to .03.

I am not sure about the clearance for the LS1, but I can tell you that when I go to start up my car in this 20 degree weather, my LS1 has too much side clearance, at least in what appears to be cylinder 8. That thing slaps its ass off when cold. I can really see GM using the hypereutectics to keep the noise down on the engine, because the amount of noise my engine makes in the cold is unreal, and I can't imagine having the same amount of noise present on a $65,000 car.

I think some of us have become too critical GM. If your doubting the z06 engine, you'll doubt anything GM ever makes. So far all the info on this engine's "problems" is just word of mouth...gossip.
Come on guys, theres better stuff to be worrying about, like what color the 5th gen display car will be. :D

My LS1 engine may slap its ass off when I first start it up, but it has never consumed oil, which is a known problem for LS1s, and runs reliably everyday, no matter how much I abuse it. I would love to have an LS7 in it, whether it slapped or not. I just can see someone getting very pissy over putting down $65,000, and having a noisy engine. Hell, GM may very well have gone with hypereutectic pistons because they are cheaper. I am not trying to say I know why GM did, but I would bet that on a motor like the LS7, they would not go hypereutectics for no reason, and I would doubt that it would be cost. The engine has Ti connecting rods for Christ's sake, and I know that even though the Ti rods in the LS7 are only forged (I believe most aftermarket Ti rods are billet), they still have to cost a sh*t load.

LS1 pistons are hypereutectic, too, aren't they?

Yeah, they are.

hyper crap pistons don't take to nitrous or blowers at all.

Not true. There have been many a LT1 that has used spray or boost on the stock bottom end with success. The key is to be smart and conservative. Hyper-u's can take it, but of course they have a lower tolerance for detonation/pre-ignition than forged or even a hyper-u w/ a thicker skirt.
The Ford 3.8L supercharged SC's use hyper-u's.