Melted Pistons Only On Intake Side?

[Shockster0429]

Here are some pics of the damage this is the #6 cylinder piston and it is the worst. All 6 of them were damaged. Also a few close ups of 3 spark plugs, as far as I can tell they show no signs of pre-det from what I can tell. Just carbon/oil marks from being rich and well burning oil due to serious blow by.

As you can see in the pic the damage is ONLY on 50% of the piston all on the intake side. The exhaust side of the piston is as smooth as they day I bought them...

Timing was 16 degrees WOT @ 16-17 psi through the 67mm. 2.7 liter 8.5 to 1 compression. Super super conservative. 93 octane A/f's were 11.0's WOT till 7250rpm were I was letting out. Intake temps around 30-32 C, coolant 88-92 C. I didn't appear to be having EGT issues during this time. It was before when my exhaust adjustable cam gear was super retarded w/o me knowing (finally found the issue) and I was missing 50% of my power when my manifold/turbine housing would be glowing as red as a stop sign after a pull or two.

Question comes down to what does a knowledgeable person on reading pistons feel would make it only melt on the intake side?

[The Mafia]

this is a weird one, I have no ideas

[Adriano]

My guess would be it has something to do with the exhaust cam timing issue.

[Lithium]

Thats crazy, I would be clutching at straws really to give anything haha. Is there ANYTHING else about the setup that you think you could share? What kind of air filter were you running? Its a bit weird there isn't obvious pitting/strange shape in the piston - ones I have seen from lean run or det are usually a lot less "smooth" than that, its almost like its been machined and I'm sure you'd have mentioned if the spark plugs had melted or anything like that. Its rather odd.

The more I think about it, the more I think its gotta have been detonation.... did you have knock mic on it etc when tuning?

Edited August 21, 2008 by Lithium

[unique1]

i have had something similiar happen to my rb27 in the past making big power (600hp+). Mine didnt melt any plugs but did some serious damage to 3 forged JUN pistons and the other 3 were starting to go as well, also on the intake sides only, cylinder 1, 3 and 6 from memory. My head looked the worst, have u got any pics of the chambers of those cylinders to see what its like?

how much power u pushing at the time?

send me a pm with pics if u like and i can let u know what was causing mine.

Edited August 21, 2008 by unique1

[RPMGTR]

"Super super conservative"

Um no.....you have detonated it to death.........

See the pic with the side of the piston eaten away....det does that, and yes generally on the intake side.

16 degs (altho it may sound low) can be way too much sometimes, it all depends on the individual engine/setup.

Some combos only cop single digits, while others love 25+...

[RS500]

i would be pointing to detonation aswell, especially given your comment about the fuel you used - '93 octane'

[VB-]

i'm willing to bet he's in the US, meaning '93' is actualy about 98 by our standards (give or take a bit)

[zeko33]

thats wat happened to me, except all 6 pistons were just fktttt....... It was the bad fuel and topped it when i took it to echuca ....... My friend has access to echuca Airport after hours and its insane man....... but ye now a rebuilt engine with forgies and i will never treat her with standard unleaded again.... Giving my 33 normal unleaded is like slapping god in the face.... YOU JUST DONT DO IT hahahahahaha

[Martin HKS]

Looks like a big case of too lean.

Why it does it on the intake side is due to cylinder inefficiencies on intake. Swirl in the chamber or intake valve shroud or short side radius air flow etc etc. will cause one part of the piston/chamber to have a problem with detonation first.

I suggest you find a new tuner if they reckon all is well.

Cheers

Marty