always faster

iTrader: (6)

So after a pass on the dyno may car began to smoke and the dispstick had pop really high with a good flow of oil :ack: I took everything apart because my new blcok is coming home in maybe a week or so.
The no 7 cylinder is busted,again since i got a new block coming i dont really care .Here are the result in pics:





My pass side head is perfect(of course) but my driver side head got some small pieces of the pistons stuck on the valve rod(seems to be melted) and some other fragment on the face of the heads(just under the intake valve),no hole on the face of the head.I took a lot of the fragment carefulley with a scrapper and a 800 sand paper but i stopped because i dont want to risk to mess those heads. They are less than 300 miles new (PRC LS6 2.5 CNC).The valve still seal perfectly and when i push it down the rest of the rod is clean.







So do i need a new exhaust valve ?
Do i need to take it to a machine shop or i can just continue to sand the fragment ?

Thanks
Eric

Old Geezer

iTrader: (3)

Detonation is the probable cause..Compare the 2 cyls.. 5 looks to be contaminated w/ oil. 7 is fried dry...
The head[s] have to come apart, and the valves checked. If you see the piston melted onto the #7 stem, it could be on the valve faces, too.
Injector failure?
Fuel psi good at WOT?

remauto1187

iTrader: (1)

I second the detonation. That will melt a piston in a heart beat. Looks like your pistons(s) melted all over the place. You got something causing detonation. Leaky fuel injector, Low octane....Your tune.

always faster

iTrader: (6)

My AFR on the dyno session was 12.8 all the way,so its not a fuel issue?
I always use premium 91 octane gas.
Maybe too much timing could have done that ???

JS01

iTrader: (10)

Hard to tell from the pics but it looks like it was detonated pretty bad. Does the piston have a sandblasted finish near the top or is that just a bad pic.

A.R. Shale Targa

iTrader: (2)

Definite on detonation...What's the compression ratio w/those heads ????
Factory timing in usually about 21deg. total...Most tuners bump that to
23-28 depending on combo but IMO 91 octane (especially 10%MBTE)
will not support the higher timing like 93-94 octane will...FWI cam timing
also plays an integral role in cylinder pressure(cranking compression)

always faster

iTrader: (6)

Yep the top of the piston looks like it has been sandblasted

Right around 10:8:1
My timing is at 27-28 at top

always faster

iTrader: (6)

Could a leaky/pinch/not perfectly sealed intake port gasket done this result ???

LS1-450

iTrader: (33)

Maybe. If un-measured air is entering the cylinder, it may run lean enough to pre-detonate. Sounds like the combination of things. Intake runner leak + 27-28* of timing + 91 Octane. Usually, 26* of timing @ WOT is around the highest depending on compression & fuel. 27-28* on 10.8:1 doesn't jump out as a definate issue as long as the tuner checked for engine knock @ WOT. Personally, I'd have the timing maxed @ 26* without knock (log for knock to check) & always use 93 octane. Any time that your not using 93, don't make any full throttle pulls & it will be alright.

always faster

iTrader: (6)

Heads are gone to the machine shop.

Trying to find a place to check my injectors without the cost of a brand new set

defaultexistence

iTrader: (11)

To much timing caused detonation , to much heat and not enough ring gap caused ringland fail..

always faster

iTrader: (6)

My 383 will be here in less than 2 weeks(callies/wiseco).What kind of timing should i be aiming for with a 240/244 .608/.612 on 113lsa with some PRC 2.5 CNC LS6 heads and 11:1 CR.

Trying to prevent any issue

Thanks
Eric

LS1-450

iTrader: (33)

Pretty much already answered. Log knock sensors to confirm. If there is knock, reduce timing. 26*is average max. that most can achieve without pre-detonation during WOT, 12.5-13.0 :1 A/F ratio @ WOT, RPM dependent.

For reference, your car will be running timing in the mid to high 30's or more @ idle.

always faster

iTrader: (6)

Thanks for the info.

But i would like to ask a question,not to argue but only to learn

My friend got a 2002 ss with a ls6,ms3,fast 90/90,prc 5.3,9 inch with 4.10 and all the bolt on.He run 91 octane gas only and his peak timing is 31 degree.The car made a a huge amount of drag and currently run steady high 10s. A lot of my other friend got cam only car ,still running 91 octane gas but 28 degree of timing.Neither of them got knocking or pinging problem with a steady 12.8 AFR

I mean,i was running a g5x3 wich is close the the ms3,the same FAST setup,same injectors and was running some slightly better heads than the 5.3 with less timing than him (28).It wasnt pinging or knocking,we log it on the dyno.The fuel data was perfect straight 12.8 too.So really close to the same setup and you see what happen with mine.

So are they all very lucky or im the one that is not

JS01

iTrader: (10)

Best way to go about it is to read the plugs or hop on the dyno and found out.

crainholio

iTrader: (2)

#7 cylinder seems to be the most failure-prone on the LS1, based on reading posts here. Theories have been presented that it's due to the lack of a coolant outlet at the rear of the cylinder heads on '01+ engines, but no conclusive data has been shown to my knowledge.

I can think of three possible explanations for your relative misfortune:

1.) You had a vacuum leak at #7 intake seal which allowed that cylinder to run lean.

2.) Your #7 injector was underflowing relative to 1,3,5. Bear in mind that your O2 sensor is seeing all 4 cylinder exhaust outputs, and the PCM operates on the presumption that all injectors flow the same rate when pulsed...one injector out of spec will cause mayhem.

3.) Their engines are detonating as well, and just haven't let go yet.

JPH

iTrader: (2)

Keep these engines @12.8 afr, 26.5* max timing on 93 octane and #7 will live along time, otherwise anything leaner or more aggersive timing will kill this cylinder over a period of time.

josh4ku

iTrader: (10)

I have broke the ringland on #7 twice now. After the second time I send the injectors in to be flow tested. 3 injectors were 6% richer than all the others. I am guessing that 7 did not have one of the richer injectors. Now that I know the flow numbers of my injectors the leaner ones are going in the back. To much air gets to the back of the intake which causes the back to cylinders to run lean. From what I have seen the fix is to find out the flow numbers and put the leaner ones towards the back, and avoid detonation as much as possible.

disc0monkey

iTrader: (10)

Just gonna fix this typo...

From what I have seen the fix is to find out the flow numbers and put the higher flowing ones towards the back, and avoid detonation as much as possible

josh4ku

iTrader: (10)

haha thanks!