Vette5.5

As a contract engineer I frequent G.M's Warren, MI tech center, recently driving my new Z. Some tech's are saying the LS-7 motor has junk pistons and are prone to failure. It's quite easy to spot the doom & gloomers(these guys are it). Having assembled several engines myself and toured the Wixom, MI special engine facility, the build quality of our LS-7's is very good. There have been a few reported failures, plus the engine exchange evaluation program. I'm not terribly concerned, especially seeing some owners running their new Z's so hard. These tech's might be a bit gloomy, but do know a few things. I'm keeping mine stock, possibly a few bolt on's, so exceeding the stock warranty design shouldn't be a problem.

yell03

I am sure they are more than fine for the stock power which is amazing already and besides,

That is why you have a warranty.

My 2001 Viper GTS had cast pistons, and lots of guys I knew threw a blower on and as long as they stayed around 550-650rwhp they were fine

Earlier Vipers had Forged pistons and could be pushed over 800rwhp easily, but where the heck are you gonna use that.

Enjoy your car and don't let the doom and gloomers try to rain on your parade.

Howard

outnumbered

Unless your a weekend warrior at the track you wouldn't normally have use for that kind of power anyway.

Redline Motorsports

The Z's stock pistons are good enough for the bolt on stuff we are currently playing with. Boosted and spray applications will be on the edge. The other issue are the Ti rods. Everyone thinks that Ti rods are bullet proof. They are actually very brittle and will not handle the future mods these motors will take. GM went with Ti to keep the weight down and knew they would handle the 500-575 hp range all day.
Anyone looking to do a serious build with the LS7 needs to put a piston/rod budget # in the plan.

GM will never use a forged piston due to noise.The cast piston is a great piston if kept within its boundries. Look at the crap they took from "hold engine piston slap" problem.

yell03

I go to the track a couple times a season.

Considering a bone stock Z has went 11.3s@127, I would say that is enough power even for a weekend warrior.

On average they seem to be running 11.7-12.0@123-125, and that is still more than enough power, at least for me it is

Howard

Paul Vincent

Of course the Z06 has enough power for the street; however, just for the sake of knowing, what would forged pistons cost? Anybody have an idea?

NORTY

Check these guys out for pistons...www.kb-silvolite.com

Forged or Hypereutectic products.
Listed for the 427,but doubt for the LS7. Maybe future?...
Neat comp ratio calculator,though.

Katech_Zach

We have developed forged pistons for the LS7 in 11.0:1 and 12.0:1. They are hardcoat anodized and weigh less than stock pistons. We also rebush the connecting rods with a solid bronze bushing. Parts and labor if you send us your pistons/rods is $1910.

yell03

I'm a hypocrite, telling you it is enough and researching a Whipple Blower and 575-600rwhp for my Cobra 10 minutes later

Howard

Patrick McDaniel

I wasn't aware of a stock car having piston problems.

Modified cars are another matter.

ZL-1

The guys at the Tech Center were probably referring to the early piston problem that was corrected before production of customer cars started. The guys at Wixom had to put in a lot of overtime changing pistons in motors built before 6/15/05. This was kept quiet, but may be the reason that Z06 production, originally scheduled to start in June, was delayed until late July. Don't know if those first few hundred "captured fleet" cars have the original pistons or if they got changed.

Mark Gray

So far, my pistons are fine.

Mark Gray

Mark Gray

Yeah, but I put a shot of 150 NOS on my cammed baby and there was a lot of noise on the 2-3 shift at 140. And the car just kinda went quiet. What do ya think that's about? Maybe the pistons really got pissed?

Mark Gray

This is not acceptable. You should contact your dealer.

glass slipper

GM uses forged pistons in plenty of their crate engines with no noise. I have forged pistons in both of my 467s in my boat with no noise. Forged pistons do require more piston-to-cylinder wall clearance due to the extra thermal expansion, but if you set them up to the low side you won't get piston slap. The "all forged pistons make noise" is an old wives tale. The ones set up to the high side will but you can't make a blanket statement that all of them make noise based on a few that do.

The reason GM stays away from forged pistons is for 1) better emissions, 2) better fuel economy, and 3) more horsepower (yes, more HP!). 1) The extra clearance provides a place for the fuel mixture to "hide" above the top ring and gets exhausted as unburned hydrocarbons. This is the reason the top ring land has moved so high on the piston, to reduce this volume even further. 2) A forged piston transfers more heat to the underside of the piston which reduces efficiency causing a reduction in MPG. 3) And finally take two engines built exactly the same except for one with forged pistons and the other with cast hypereutectic pistons, the cast piston will make more horsepower since the forged piston transfers more heat and heat is horsepower. Of course that is true only up to the point where the cast piston gives up and you end up with a rod sticking out the side of your block. At that point, time to go forged.
As you noted, the stock pistons are good for bolt-ons. They will even handle small amounts of boost or spray if you stay away from detonation with a good tune as you well know.
Also, Ti actually has more ductility than steel (it's not as brittle). The problem is Ti is not as strong as steel on an area basis (per square inch). So the Ti rod has to be made large in cross-section to have the same load carrying capabilities as say a forged 4340 steel rod. Its' lighter weight more than makes up for the extra material, but the rod is dimensionally constrained by the inside of the engine and you get to a point where you simply can't make the Ti rod large enough to handle the load. But your point is well taken, if you're gonna add lots of HP, put new rods/pistons in the budget.