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....

 

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.

 

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

 

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.

 

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.

 

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?! ), so on a practical basis, the LS7 pistons could be made of glass for all that affects me.

 

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

 

But the Z06 badges alone are worth $15,000.

 

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

 

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

 

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.