Quickin

What moron at GM decided not to use a good set of forged pistons in the LS7 motor and use all good stuff everywhere else?

If there's a good reason...OK...if not the "moron" stands.






.

stik6shift93

From what i understand forged pistons tend to expand more and require looser cold tolerances than hypereutectic, which gives more cold start emissions. Don't know if that's the reason or not but i suspect there's a very good reason, i'm sure if they're already putting titanium parts in the motor, a few extra bucks to run forged pistons wouldn't make a price difference that would prevent them from using them. It definetly would have been nice if they did go forged though, that thing would take a 200 shot all day long.

-Joseph-

iTrader: (12)

Probably to stop ppl from bitching about the cold piston noise, remember who's buying them...

I have heard that GM has made a forged piston that you can buy over the counter that can be installed without re-balancing into the LS7 engine.

Richiec77

iTrader: (3)

Cold Start Emmissions is the #1 factor. It would DEFINITlY not be an LEV if those were in there. Also Piston slap is one, and for a True Street motor (OEM is that) Hypereutectic is the perfect piston to use.

Spinmonster

My car isnt tested cold and I doubt it would fail if it was.....yes forged pistons...... and so that is as much as I think of the forged piston theory and emissions. Maybe they just cheaped out like the Z06 190 dollar a set shocks.

Quickin

What state does cold start emmissions testing?

Don't you drive there to get tested?

Quickin

I have forged pistons that don't slap and I drive mine every day.

Can GM not build an engine as good as ARE so it doesn't have piston slap

LS2 V8 Miata

I thought the Hypereutectic pistons were supposed to be superior in many areas IE coefficient of expansion, high Silicon content resulting in weight savings and unlike normal aluminum forged pistons, high silicon content in the presence of high heat is supposed to further strengthen the piston, not weaken it?

Automotive materials specialty engineers please enlighten us lay people that just want to go fast

SSCamaro99_3

iTrader: (1)

Most of these people are not talking about state emission testing, but EPA emission certification for a production vehicle.

Spinmonster

And the fords all come with forged pistons for 1/2 the price; cobra, gt

Quickin

I just don't see how a cold start emmission can be different from a non-forged and forged piston going up and down in the cylinder....whats up with that?

zamboxl

iTrader: (1)

wait i thought the ls7 was geting cast pistons not hyper.

Ravenous T\A

iTrader: (12)

I dont get it?!?!? LSx motors had piston slap with the hyper pistons, so they use those same style piston in there big dollar LS7 motor?!?!?!

Greg Fell

iTrader: (9)

Didn't they also have a gas guzzler tax ($1000)?

Var

iTrader: (1)

If they havent expanded to their full size they will hold less compression and cause more CO emissions when cold.

Quickin

I would think a fully expanded piston would hold more CO. The one that is less expanded (cold) would allow some to escape into the crankcase.

RIGHT?

stik6shift93

I wasn't referring to your emissions test that you take but to the certification from the epa that they do on their own. I think var explained the reason for emissions, in addition when the pistons aren't fully sealing you burn a little oil which is bad for emissions. I don't know whether or not that is the real reason, just seems like a logical guess, i would like to hear somebody who actually knows what the reason is. From what i understand they have the technology to create forged pistons that expand minimally, close to that of a hypereutectic, so who knows. Under naturally aspirated conditions hypereutectics are a great piston but they're to brittle for boost and nitrous applications, gm obviously didn't design the motor for those applications so maybe they just don't see a point to putting forged ones in there.

1BadAction

iTrader: (10)

there is cold sieze problems with forged pistons, unless a few thousandths bigger bore (or smaller piston, in the cars case) size is used. that means worse emissions on cold start.

regular aluminum is fairly easy to forge. The more silicon that is added to the aluminum, the tougher it gets. Eventually it gets to a point where the Dies wont last long enough to make it worth the extra silicon. Normal hypereutectic pistons arent weaker than forged because they have a high silicon content, they are weaker because they are CAST. of course, super high silicone content makes the piston brittle, but I havent seen any pistons that bad.

one company makes forged AND hypereutectic pistons. MAHLE forges pistons with a Silicon content more than 12% which is high enough to be considered hypereutectic. these have all the Benefits of a forged piston, with the expansion properties similar to a Cast piston. that coupled with coatings that are application specific makes for a superior piston, IMO. German and British tuners have been using Mahle pistons for years under High boost, continuous high Rpm duty (autobahn) and in my boats, I've spun Mahles 7500-8500 for 20-30 minutes at a time with EGTs up around 1200 degrees, they hold up awesome. I cant figure out why they havent caught on over here. other than possibly the price.

Quickin

I see most things don't get here until after the rest of the world has them for awhile, like the Aussies.

Spinmonster

And the point has what to do with performance? If a cobra has a gas guzzler tax it has nothing to do with how good a bottom end is. As if a forged piston now affects gas mileage. I wont be checking back on this thread....just stupidity.

A freekin mercedes has forged pistons.