Overheating Verdict: blown headgasket allowing cylinder pressure into the water jacket, boiling the water out until there isn't enough left then it overheats.

Piston top destroyed from failed spark plug. I haven't pulled the piston out yet, but there are NO signs of detonation on the piston top. Cylinder is lightly scored (from spark plug debris?), so I'll hone it and throw in 4 new 8.8:1 JE's next week. So long high compression, hello easier tuning.

Pics to come.

Shitty.

You were running 9.5:1, right?

yep, 9.5:1. Here are the pics:








Shitty pic, but you get the idea.

i'd say the low compression numbers are more likely from valve damage from the debis present in the cylinder than damage to the actual piston or cylinder bore.. just food for thought.

I will be checking the valves out, but the only apparent damage to the head is the quench area on both sides. I thought it was interesting that only the quench areas were damaged on both the piston and the head. Unfortunately for the piston, I would never be able to get rid of all of the high spots (which would become hot spots - can you say pre-ignition?) so I have to replace them, even though they probably seal fine. I think the compression leak is from the head gasket going.

That sucks man, hope ya get it all back together soon..

I was talking to my mechanic at Mitsu today telling him I wanted to turbo charge (Hahn Stage II)by next summer and he said to be careful b/c the 420 pistons are casted alum. and don't stand up to it very well. He actually recommended Nos, which I thought was funny. Anyway, I've heard what he said before but the exact opposite. And now I see this thread on here about pistions. So what's the truth?


AEM intake/SpiralMax/Plugs-Wires/GST Exhaust/Mirror Tint/Grillcraft grill/EBC brakes/Brembo rotors
Coming:BoredTB

His pistons are not the stock pistons and the problems that he had have nothing to do with the structural integrity of the pistons themselves. It looks like he simply got unlucky and had a plug break on him and the pieces from the plug damaged the piston and the head.

What your mechanic said about our pistons being cast is true, but as many of us can testify, they will hold up to 7-8 pounds of boost (HRC Stage 2) for a very very long time if tuned properly. I started boosting my car about a year ago (13000 miles ago). I had about 79000 miles on the engine when I started boosting. 1000 of those miles I boosted 12 psi which is more than anyone recommends and when I tore apart my block this past week, the pistons looked fine and the cylinder walls looked like they were still brand new. So, to answer your question, yes the pistons can take it, but once you change over from n/a to turbo, you need to be prepared pay to play because shit definately happens.

I appreciate your comments and find them informative. If you don't mind me asking, what kinds of things have you had to "pay to play" without going crazy on detail :7



AEM intake/SpiralMax/Plugs-Wires/GST Exhaust/Mirror Tint/Grillcraft grill/EBC brakes/Brembo rotors
Coming:BoredTB

just a headgasket so far... everything else I have done by choice rather than by force :thumbsup Lets hope it stays that way hehehe

I would really look into getting your cylinder head decked/milled. The stock MLS headgasket is bullet proof, and in no way that should have leaked like that if installed properly, and if you used the sealant spray on the gasket on assembly. My guess is that, improper HG installation, or a warped head caused the leak. Another guess is that with the leaking coolant into the combustion chamber, it causes a rapid heating-cooling effect on the spark plug, witch can weaken metal, and it broke.. Also, if you can feel the scratches by running your fingernail over them, then you most likely will have to bore the cylinder, not just hone it...

I am having the cylinder head surfaced, hopefully they won't need to take off too much. I don't want high compression again. As for the cylinder walls, you can *just* feel the scratches with your fingernail, but you can't get your nail *into* them. The deepest scratches are at the very top of the cylinder - where the rings can't reach.