cooler stat from where??

before I get the drill out.

David

Bore distortion causing the piston to wear abnormally. That piston looks like all 4 that came out of my original 2.5 NA donor engine

Paul

From where? Hoping you would tell me :)

Bore distortion from overheating Paul? So too lean or poor coolant flow? If all four did it could it be a coolant system failure of some sort?

In the short poll in the second link above almost 2/3 of failures have been #4.

right, thats it.. when my headers come off to be ceramic coated and to replumb the wastegate.. Im going to put an egt in each collector too.. for the cost it would be rude not to..

David

Reposted the original - sorry edited too many times, trying to get the picture right :)

http://forums.nasioc.com/forums/show...hreadid=416756

http://forums.nasioc.com/forums/poll...ts&pollid=4483

Suggestion is not due to fuelling (apparently APS tested this) but due to coolant hot spots on the back side of #4. 2.5RS and WRX have a similar failure pattern.

http://www.johnbanks.dsl.pipex.com/4.jpg

Cooler stat? Water wetter? Richen up #4 a bit?

Discuss :)

It could be as basic, as a distorted bore, caused by residual stresses being released as a result of heat treatment.

If there was some local overheating it could have done this.

The main thing is the wear on the piston, and the broken land, which appears to have been caused by the bore almost crushing the piston. With the clearance gone, and oil displaced you will get a partial seizure.

If the bore had gone the other way, i would have expected the bottom edge of the skirt to be more damaged.

If the piston got too hot itself, it could have had the same effect, although you would be able to see that in the form of "death ash" on the top.

Why #4? Well, hang on, I thought it was #3 that was always going? You're not telling me 'they' have changed their mind have you?

Paul

[caveat]I know little/nothing about high performance tuning[/caveat]

Stuff that jumped out....

Most of the reports are from UTEK or Unichip maps. Nothing from Vishnu (tek). Are they mapping to safe or p1ssing contest levels ?

None of them appeared to run what we would consider 'normal' monitoring ( knocklink, afr etc )

These all seemed to be in relatively high states of tune 300whp (370+ fly ???) on US gas. Even the 92-93 octane gas may not be enough 93octane ~ 97ron ??


Just thoughts .. feel free to ignore :)

JB, Sorry, just caught up with this thread. That picture shows a classis case of detonation failure. The vibration set up by det shakes the ring lands and they fracture of exactly like yours. In the 'text book' that would be a perfect picture to use.

IN MY OPINION

Pulsar GTI R's do it all the time and it's a well known pheno, phenom, phe, problem !

David API

Not mine thankfully David :D yet ;) If detonation control is "all" that is required then I have nothing to worry about. If it is pre-ignition from hot spots because of poor coolant flow then we are all doomed unless we tune them very soft.

John, I'm sure it's been said here before, if not by me then by others, these engines don't suffer anything like these failures in Japan where they run on 100 Ron. And yet over here with combinations of Opti and Octane boost and other tricks we still get these problems. It's my understanding, I believe that SUL and octane boost still doesn't equate to 100 ron in the pure sense but is a confusion of chemicals that fools everybody [thing] but that may be folklore.

I would need a deal of convincing about hot spots and water flow and so on before I would really consider it to be a problem that required drastic research.

In my opinion det changes a whole load of characteristics in the engine, spark too soon and you're firing the gases in the manifold before they get into the combustion chamber and a whole load of parts get subjected to unusual heat. It isn't just restricted to the crown or sides of the piston when det occurs.

Not sure if this comment leads anywhere, just more info to consider really.

David API

No. 4 went on mine!

Scott

have any pics of the piston ?

Carlos H.

No, its still in the engine ;) and will be for a few weeks at least!