Sharp Piston Edges

[Joryn]

One other thing i should note was the noise the car made whilst it was running. Normal operation was perfectly fine, no pinging/knocking or anything. as soon as the car was under boost something like bad rattling came from either the engine bay or something loose in the dash. I couldn't ever find anything in the dash so unfortunately that rattling is likely from the engine bay.

The question being is this another symptom of piston slap? from what I understand slap should be heard at all times, in my car it idled and cruised noise free (aside from typical valve train noise). This rattling was a boost only problem. amount of boost didn't matter. I heard it at any boost level (7, 10, 13). I don't know if that helps clarify the issue, or just makes it tougher to figure out but I thought it best to mention.

Joe

[turbovanman]

You would hear piston slap all the time so on that note, sounds like your detonating badly under boost, hence the jagged edges and blown head gaskets. What kind of fuel are you running? are you running an aftermarket cal? how much boost?

[Joryn]

Fuel at the time of knock was always premium (91 is best we can get here, 94 if we get ethanol blended), cal is a 86-7 GLHS STage II, boost was bypassed as best I could (wastegate into vac manifold) and usually maxed out at 10-11 psi. So nothing serious that would cause the knock.

Unless a lean condition a fairly long time ago caused the piston ridge, which made the cylinders prone to pre-ignition which is what caused the problems with blown headgaskets. I do recall a 1/4 pass where boost spiked to 18 psi and settled to 14, could have caused problems but on forged pistons?? It just didn't seem that likely.

[turbovanman]

Weird. Maybe your lean? cam timing out, base timing out? Too much compression from head and block milling so now its super sensative, crappy intercooler?

[Joryn]

Hmm, lets try answering those one at a time.
Lean: I checked the fuel system at a shop recently, fuel pump is new, fuel filter new, injectors and rail checked out accordign the specs. It is possible I had a bad FPR, might have to check into that.

Timing: while possible I don't believe that it woudl be out by that much (maybe 1 tooth) and from what I understand this isnt more then a few degrees advance/retard. Not enough to cause this amount of detonation. Also the dist timing was set pretty conservatively at 10-12 degrees.

Compression: No milling has been done on the head or on the block so this is unlikely.

Intercooler: It's not the most effecient but it flows really well and is quite large (ebay unit 24"x9"x3"). The cold side is always quite cold at the track.

I'm going to have to pull the head off soon, pull the pistons, look for damage and see if I can find anything else out. as a side question will I have to replace the rings if I pull the pistons out of the cylinders? I'd like to keep this fix as cost effective as possible.

Thanks again,
Joe

[XxPichulonxX]

Quote:

Originally Posted by Joryn Intercooler: It's not the most effecient but it flows really well and is quite large (ebay unit 24"x9"x3"). The cold side is always quite cold at the track.

Lean more towards efficiency than more flow... too much flow won't let the air charge sit long enough to dissipate its heat, but cheap is cheap.

[turbovanman]

Quote:

Originally Posted by Joryn I'm going to have to pull the head off soon, pull the pistons, look for damage and see if I can find anything else out. as a side question will I have to replace the rings if I pull the pistons out of the cylinders? I'd like to keep this fix as cost effective as possible. Thanks again, Joe

Before you pull the head off, perform a leak down test, this will tell you how much the rings are leaking-if at all. If the leakdown is good, then when you pull the pistons, just make sure the rings go back in the same bore.

[Joryn]

Quote:

Originally Posted by XxPichulonxX Lean more towards efficiency than more flow... too much flow won't let the air charge sit long enough to dissipate its heat, but cheap is cheap.

Yeah I know that fully, but the price was right and from what I can tell it does a heck of a good job so I"m pretty satisfied. I haven't gone so far as probing in/out temps but that might be worthwhile...just to see what this style of IC can do.

Quote:

Originally Posted by turbovanman Before you pull the head off, perform a leak down test, this will tell you how much the rings are leaking-if at all. If the leakdown is good, then when you pull the pistons, just make sure the rings go back in the same bore.

I don't have a leak down tester at my finger tips nor do I know where to get one easily. All i can say for sure is that compression is pretty good (~120 across). I know that doesn't say the same thing but still it's a good sign. also to note is that there's no blowby that I can see either. Any ideas on how to do a quick easy leak-down test?

[turbovanman]

Quote:

Originally Posted by Joryn I don't have a leak down tester at my finger tips nor do I know where to get one easily. All i can say for sure is that compression is pretty good (~120 across). I know that doesn't say the same thing but still it's a good sign. also to note is that there's no blowby that I can see either. Any ideas on how to do a quick easy leak-down test?

You can rent one, there cheap. There is no easy way without the tester. You can still have good compression but leaking rings.

[Joryn]

For those who are interested in what happened to this engine, check out this thread :
Damaged Pistons