C20LET - Fried forged pistons nr. 2-3, 1-4 ok

[Pet]

These Wiseco's were 8.5:1, low temp thermostat (82C) and 100 octane fuel.....

[GintsK]

 It is not considerable as "conservative" map. It is weird map - retarded, where it can be safe at almost any advance and advanced in dangerous area. If your engine was not tuned, result is as it should be. Some seconds with hard knocking and - done. Also you use original hot spark plugs. IMO it is not a safe way. Black dots on isolator was months ago. Usually it is from knocking.

 It is rare when all pistons are melted.

Gints

[rob@vems.co.uk]

I'm looking at this:

What is the deck surface like between 2&3 especially in the area where those two black half moons are?

They look as if they might be pitted.

Also can you raise the pistons so that we can see the crowns more clearly?

[MWfire]

your map is very bad, probaly knock at 3000rpm. At high rpms you need more advance, no less.
here is little retarded map for c20let 8.5:1, safe map(not for max power).
http://img263.imageshack.us/img263/5743/mssparkv2set3.jpg
btw opel c20let stock exhaust mainfold is crap, cly 2 and 3 have many better flow.
what is your trigger tooth and rising or falling?

[Pet]

your map is very bad, probaly knock at 3000rpm. At high rpms you need more advance, no less.
here is little retarded map for c20let 8.5:1, safe map(not for max power).
http://img263.imageshack.us/img263/5743/mssparkv2set3.jpg
btw opel c20let stock exhaust mainfold is crap, cly 2 and 3 have many better flow.
what is your trigger tooth and rising or falling?

Thanks,
  my trigger tooth is 8, trigger angle 68 (was 74), rising edge.
Here are detail pics of piston 2 and 3 + head is destroyed too

[rob@vems.co.uk]

That last picture is a perfect example of detonation.

[NOTORIOUS VR]

That doesn't look like an overly aggressive timing table @ all...

[rob@vems.co.uk]

It doesn't have to be aggressive to get detonation.
If the inlet temperatures are too high, or the octane too low (I know that this was running 100octane fuel) then detonation can occur.
In this case it may be possible that the timing was out on cylinders 2 and 3, or it could be that the water flow was not right and the middle cylinders overheated and that this started the detonation.

[MWfire]

i take a look to my c20xe settings, and i have trigger tooth 9 and 69deg.
So 9*6+69=123deg, and you have 116, so you have 7 deg advance more than me. My setup is 100% correct for that type c20xe. So scope your engine again.

[GintsK]

I have 6*9+63=117
 

[Pet]

Thanks, I'll check it, asap I get some new pistons and head....
Here is detail of one melted piston, I must say, the most upper ring was very strong to hold together....

[MWfire]

I have 6*9+63=117
 

as i sad, i saw two types of trigger wheel on c20xe(123 deg is from one c20xe with motronic 2.8. That c20xe has heavier flywheel and blue injectors(241cc)). Difference is 6deg. So you can't only copy config for c20xe.
So far did 4 c20xe and 2 c20let, and two have 123 deg, 4 have 117deg.

[GintsK]

Ah, remembered: "LET" was builded from XE !

[Pet]

So the engine is running again and I have really 117deg version, so now I have trigger tooth 6 and 81deg angle, checked with timing light. Thanks.

[max]

And remember that you shouldnt drag-race before you your car is correctly mapped