Why a broken ring land @ 10psi with mahle?
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
Most of the MAF codes I've seen dump the car into SD mode. The VE table (for speed density) is usually left alone when you get a MAF based tune. While in SD mode, the car may have fuel trimmed its way back into running decent at part throttle, but it is like Ray Charles at a gun range under WOT.
Under, or fail (revert to SD) could have caused this. That's a 2/3 chance lol.
Doesn't matter how it failed, the fact that it threw a code means it went into speed density and that's what will always happen with a MAF code.
8 sec potential, 12 sec slip
iTrader: (50)
Joined: Apr 2002
Posts: 4,092
Likes: 2
From: Savannah, GA
Yes, but WHICH Mahles were you using? The flat tops or the dished ones? I ran the flat tops (-4cc valve reliefs) with 16psi and had no problems with them, but the ringlands on the dished Mahles suck ***** apparently from every experienced source ive heard from...
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Brett Foote
Just do yourself a favor on the next build and get a wb o2 then you will have peace of mind about your tune and any ses light that may come on......I know lesson learned the hard way. Sorry about your luck
On The Tree
Joined: Aug 2007
Posts: 112
Likes: 0
From: Finland
Thinking of ordering wisecos. 
there are quite a few documented failures of Mahles...with no detonation...just a structural failure of the ringland. there are far better pistons out there IMO.
Chad
I agree 100%. What my new engine builder told me was they have the wrong silicon content for anything above 10lbs of boost. My motor was on a break in tune and a piston ring land fell apart. Rebuilt the engine used the same brake in tune and no problems with the new engine.
Damage - piston last the top ring land - material in the pistons used was Alloy 4032 - the pressure of the boost simply broke the piston - here's an description of 4032 and 2618 alloys...
"there are two common alloys used in forged pistons, 4032 and 2618. Silicon-aluminum alloys, such as 4032, have great wear characteristics because the silicon particulate hardens the alloy and reduces the thermal coefficient of expansion. However, silicon-aluminum alloys can turn brittle and become prone to fracturing when subjected to extreme stress. With a piston made of a silicon alloy once a crack starts, it doesn't stop until the piston suffers a catastrophic failure. Low- or no-silicon alloys, such as 2618, may wear a bit faster but provide better strength and durability. In the rare case of a crack in a 2618 piston, the crack will migrate to an area of lower stress and stop. 2618-alloy pistons keep their shape under extreme pressures and high RPM's."
Sounds to me like an improper piston for the application. Can't blame the manufacturer for that. 4032 has about 15% less tensile strength than 2618 and is not recommended for boosted applications.
ps - mahles are forged 4032 (~12% silicon content). unless you're talking about the lsx376/454 engines that gmpp came out with (which use forged 4032s), the stock pistons are cast hypereutectics (increased si content and therefore more brittle). to even think the two are comparable in strength is asinine.
ps - mahles are forged 4032 (~12% silicon content). unless you're talking about the lsx376/454 engines that gmpp came out with (which use forged 4032s), the stock pistons are cast hypereutectics (increased si content and therefore more brittle). to even think the two are comparable in strength is asinine.
Teching In
Joined: Jan 2009
Posts: 18
Likes: 0
Its been absolutely perfect running for approximately 10k and haven't changed a thing. The whole scenario here is that I made a drive of around 50 miles coming home on the freeway normal cruising when the SES light lit. I automatically assumed it was the MAF sensor circuit as with a previous case so when I got home, it was removed and cleaned. The next drive the light turned itself off and ran just normal. Then the next time, the light came on with the ignition turned on and started. It remained on for following start ups throughout that afternoon. On my way home, I hopped on it in second gear gettin on the freeway, shifted to third then eased out when I reached speed. I shortly noticed a slight vib then soon realized it dropped a cylinder, got home and parked it a few miles down the road. I pulled plugs on the drivers as the expected misfire side and they all looked perfect till no. 7 which was broken and battered. Pulled the head off and my assumptions were realized. But why would this happen on only 10psi boost and a very good dyno tune? The engine was fully built by a very reputable builder and tuner. I have yet to contact them because it's nothing to do with the builder but will probably be ordering parts through them.
Set-up:
Stock bore, stroke, block
Mahle 9:1 forged, callies rods
ETP heads, comp cam
STS @ 10psi
Dyno tuned by builder
Set-up:
Stock bore, stroke, block
Mahle 9:1 forged, callies rods
ETP heads, comp cam
STS @ 10psi
Dyno tuned by builder