sonofthehill

iTrader: (1)

So, what are the dimples on the valves? FOD maybe?

18psi

iTrader: (76)

probably from when his pistons commited suicide

sonofthehill

iTrader: (1)

But aluminum putting marks like that on a valve face? I guess it it was moving fast enough.

sonofthehill

iTrader: (1)

And at that temperature

ysleem

iTrader: (5)

Jesus! Yeah post logs so we can see what was the true cause here

elior77

Head shop marking

Eunos91

I would assume these dots cause heat spots. Didn't they have edding markers?

Mudflap

Marking them for what? Those valves are rock hard - they'd have to really strike them to get those marks.

elior77

Marking them in order to know which goes where - I believe this is not the first head it been done to.

Could it be responsible for hot spots and the pre ignition that melted the pistons ?

Thanks
Elior

18psi

iTrader: (76)

No. You are

Savington

iTrader: (31)

Lol, fire your tuner.

elior77

I tuned it and there were no abnormal signs while tuning, could be the few 20psi peaks did the kill.

I'll try better next time - in a week or two.

hi_im_sean

iTrader: (3)

Those pistons are eroded, that doesnt just happen with a few spikes. You were consistently detonating. You need to make or get a set of detcans. There most deff was abnormal signs with the way your pistons look, you just didn't pick up on them.

psyber_0ptix

iTrader: (4)

Take pictures of that motor too.

sonofthehill

iTrader: (1)

I have heard of dimples on combustion chamber surfaces, to reduce detonation.

Just be sure to set your base timing at idle before you drive anywhere next time.

psyber_0ptix

iTrader: (4)

Never forget Singh Grooves.

Mudflap

Severe detonation can melt a piston nearly instantly. I've had pistons on a two-stroke go from new to totally melted down in less than a 1/2 lap of a track. Mild detonation can also slowly erode the softer metals. But that to me looks pretty catastrophic (instant).

On second look, those are clearly marks from the engine builder. 6 marks on intake/exhaust valve, 7 marks on another set. That is a stupid way to mark them, just use a marker pen. Yes, those could initiate detonation due to a point source of heat forming, but they aren't the cause. The cause is you thinking you can run 20psi without proper tuning and fuel.

-removed my rude comment, unnecessary-

elior77

As I said, fuel was 11.5-12 all the time (could be the sensor is off, it is my ls4.2 spartan running for 7 years now).
The timing map is @ less then 10deg from 180kpa and up (could be base timing is off I got -13deg for ecu offset).
I understand the rising edge vs falling can advance timing too.

I'll double check everything on the new build with a new digital WB and 4.9 sensor.

Thanks for the input guys

elior77

New engine to burn

Mudflap

I'm impressed, 2 weeks and you got the block re-bored and decked with new pistons? Or is that just new pistons only? No matter, I can barely change spark plugs in 2 weeks.