383ss

iTrader: (14)

I blew both of my head gaskets screwing around with the nitrous on the street and found this when I got the heads off. this is the only piston/head chamber that has any damage at all. it is cylinder 4. is this caused from detonation? if not, what the f is it and am I screwed? I was thinking I'd just put it back together and do a leak down test

sorry about the big pics, but you need them for the detail.

1CAMWNDR

iTrader: (21)

Yep. That is detonation on a large scale. Those little silver specs are molten spots of aluminum coming off the piston. You might be able to get away with polishing the combustion chamber and replacing that one piston; but I would stay away from the juice untill you can build a forged bottom end.

1QuickT-A

iTrader: (12)

How the hell did you do that? How much spray and did you tune on the car any? Obviously you have some timing/fuel issues..

383ss

iTrader: (14)

I have a forged bottom end. guess I will just get the chamber polished, not spray it and see what happens I just built this f'n motor last fall. I would REALLY rather wait and take it out this winter. do you think it would be ok if I left the piston like it is?

why would it just be in one cylinder?

383ss

iTrader: (14)

I was trying to spray a 100 wet shot.

JoeyGC5

iTrader: (24)

John, what fuel system do you have?

383ss

iTrader: (14)

for the wet shot, I built a stand alone setup. for motor, I have a walbro in tank, stock lines and LS1 speed fuel rails with 42# injectors.

CAT3

iTrader: (9)

at what cyl did the gasket blow out? If around #4 you could have blown the gasket out, sucking in unmetered air and thus detonating. How much timing? What kind of gas in the nitrous fuel side?
Seems odd it was #4 and not #7, but you never know.
What compression is was this built at?
What kind of plugs and what do they look like, specifically #4? Can you post me a pic plz?
I find this very interesting, sorry it comes at your cost.

Charlie

1QuickT-A

iTrader: (12)

I don't see how you did that with just a 100 shot and with a good fuel system like yours.. Sounds like the tuning is out of wack or there is a major problem somewhere.

I am also curious to know the answers to CAT3's questions..

DONAIMIAN

iTrader: (18)

time to invest in a wideband.

1QuickT-A

iTrader: (12)

Hell I spray 150 Wet on my stock bottom end with 112k miles with the STOCK fuel pump.. Have put about 6 bottles thru it with 125-150 shot jets.. And I'm talkin raggin the **** out of it on the spray... Goin from low rolls up to 150mph...

Something has got to be wrong with his setup...

1CAMWNDR

iTrader: (21)

Damn dude, if you are already runing good pistons then you either have a bad fuel injector, or your fuel maps/timing maps are all screwed up.....but if it was the tune I'd think it would be more than one cylinder.
One bad injector maybe?
I like this possibility also.

y2khawk

iTrader: (5)

What did the plugs look like?

Honestly, it looks more like you lost a few small pieces of electrode/ceramic and bounced them around in there for awhile.

schultzsj

iTrader: (1)

That looks like "FOD" to me (Foreign Object Damage) caused by something hard bouncing around in the cylinder.

You may have sucked something in the intake or lost a platinum plug tip, something like that. The nicks look like they have carbon in them so the damage night not even be recent or have anything to do with the nitrous.

Detonation is an explosion in the cylinder that can result in broken pistons or their lands or blown head gaskets but not the kind of damage you see there.

You should be able to just polish the nicks to remove sharp edges (to avoid detonation-causing hot spots) and re-use the head and the piston - just make sure none of the grit from grinding gets into piston/wall gap or rings.

Steve

383ss

iTrader: (14)

sorry, I did misspeak. it was clyinder SIX. timing is running around 26-27. compression is about 12.8:1. I they are TR6's, almost new. I tried to take a pic of the plug, but it didn't come out. it looks completely fine to me though, just like all the rest.

I have a wideband. I was monitoring it and it was safe ~12.5:1, it is on this cylinder bank also.

a bad injector did cross my mind... how do I test that? I think my maps are fine. my motor has run great, again, wouldn't all they cylinders be f'd up, at least not just one?

I am starting to think that also. I don't think it had anything to do with the nitrous and might have been this way for a while....
I'm having the heads planed .003 to get rid of it, and going to polish the piston a bit.

here's some better piston pics and head gasket pics. I really f'd them up





Gasket top

Gasket Bottom

JoeyGC5

iTrader: (24)

John, tpis will test/clean injectors for like $15-20 ea

Ben R

I also thought the same Harlan.

Post some good pics of your plugs.

383ss

iTrader: (14)

I'll get some tomorrow. I just remembered I changed the plugs a few months back from TR55's. I didn't notice anyting at the time, but I'll see if I still have them and take a look to see if any are jacked up.

CharlieLed

iTrader: (1)

One thing that hasn't been mentioned and could be a source of your damage (don't ask how I know) is that you may have lost some of the head casting around the valve guide. If your heads are ported and the aluminum around the lower end of the intake valve guide is thin, then it is VERY possible that a piece broke off and rattled around that cylinder until it found its way out the exhaust.

Slowhawk

iTrader: (12)

12.8-1 compression ,12.5-1 A/F and 27 degree's of timing will definitely detonate the engine.
We've pulled a few piston's that looked like that.All Nitrous cars that ran 100+ shot's and thought the cars ran fine.