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 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....

 

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.

 

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.

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.

 

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!!****. 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!! )

 

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

 

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...

 

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

 

*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:

 

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...