Metric Mechanic Pistons

[pantelones]

You should have posted this photo, it's by far the most telling... Obviously what happened is that the thinnest part of the piston gave way under heat and pressure.




My guess is bad tuning... And why a 272 cam? Do you have a pressure differential in-favor of the intake side? Meth makes me think high boost and as stated before...

If you run enough ignition timing nothing can stop the detonation, meth isn't a cure all.

[Bmwb]

that's my bad on not posting that pic didn't really pay attention , the motor had the 272 when I got it so I kept it in there .its fine either way I had back up motors just in case something like this would happen I just wanted to see what everyone thought

[LJ851]

That piston fucked.

[kronus]

based on that pic i get

thin valve relief to piston ring metal -> gigaboostu pushes piston skirt out -> piston drags up on wall, deforms valve relief -> clearance to valve decreases below 0 -> contact

[LJ851]

You should have posted this photo, it's by far the most telling... Obviously what happened is that the thinnest part of the piston gave way under heat and pressure.

Take a look at the surface roughness on the side of the piston at the upper ring land. See that textured, sandblasted look? That is aluminum being eaten away by detonation which caused massive heat and pressure and pushed the softened piston upwards til valve contact. I bet if you measured the piston it would also have a flat spot there from being pushing in as well as up by the forces.

[TobyB]

to me it looks like it got hot and deformed

beat me to it...

t

[Bmwb]

shit happens , im fine with it got a 2.8l stroker on the way , and a boosted stock m20 going to get dynoed

[LJ851]

^I hope this is another tuner than the one who made the timing map for the last one.

[Bmwb]

yea what ever , im going to toma here in Calgary everyones telling me they know there way around megasquirt

[TobyB]

Buy a WBo2 sensor rig, too. Pretty cheap insurance...

t

[LJ851]

Buy a WBo2 sensor rig, too. Pretty cheap insurance...

Truth.

[Bullhead]

That's good info, I have seen the exhaust side of a piston do that or the reverse but not the intake side. But then again I haven't messed with boosted engines much either. Good calls and info here fella's.

[DesertBMW]

That is result of pre-ignition or detonation. Result of poor combustion chamber characteristics, you can't just slap some pistons and expect it to be all OK. You got to have correct quench areas for the flame front to start ignition always at the center. As I see there the compression ring got hot so much that it acted as a spark plug.

[digger]

i would look to paul burke for turbo pistons and find a good tuner

http://www.performancepartsracing.com/products.php?cat=38

[Old city bimmer]

Metric Mechanic Pistons

By looking at the pics .... You have detonation at full boost and It was starving for fuel big time. What injectors were you running ? Definetly the tune also needs to be looked at.


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