Silly question, but you are running a rising rate fuel reg, with a return line aye?

i was just talking to jeff taylor he reckons the piston went from overfueling, he said the fuel gets forced past the rings by the boost pressure, and ignites around the ring lands and burns them away, sounds pretty logical tome... dont know what im going to do now, think i need to go searching for someone who knows how to tune dellrtos coz i aint driving it untuned again my pockets are getting worried after one blown engine ....

I dont see heaps of logic in that. I am not saying its wrong. Just dont see how it could happen. Any boosted engine is gonna have blowby under boost.
The ring lands were said to be broken, do they look burned?
Nissan has always been known to overfuel their boosted engines.

The closest logic to that I can think of that, is anything like that is what I have been told from an oldbloke that tunes/messes with alcohol engines.
Guys that run alcohol easily suffer engine problems from bad tuning. The reason being is alcohol is so cold. If they run an engine and it detonates. The next lot of alcohol to enter that cylinder is going to cool the hot metal to quick and cause problems.
Fuel is nowhere near as cold as alcohol, but enough of it will still cool without igniting.

The only way I can see to prevent unburnt fuel from passing the rings, is to ignite it as its entering the cylinder, And that just isnt going to work.

Only real way to know the cause of the problem, is to run/tune the next engine with a good gas analyzer.

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or you just fix all the probs right now with EFI.

poorly tuned EFI is just as bad as poorly tuned carbs and dissies.

I'll ask again. have you done anything to control the mechanical ignition advance?

fuel being burnt around the rings? aren't the rings designed to be the barrier of the combustion process? There is always fuel/air mixture around the rings - that's what they (compession rings) are for - to hold the explosion (burning fuel) and extreme pressues above them so they can be converted into useful work on the top of the piston...

if it was in any way caused by fuel being burnt around (ie past) the rings, there would be lots of scoring on the piston skirts where the oil was burnt off them...

bad luck kegs aye. just thought i would point out the irony of the title of the thread.

my thoughts on running it in next time
remove the turbo exhaust and use a standard exhaust put filters on the carbys and run it in as a normal engine for a few ks
then once its run in then comence putting the turbo system on. may have a better survival rate ....my turbo runs very rich indeed but when it comes on boost it certainly uses a fair chunk of gas ,Id be more inclined to say it was lean and timming .

this is a weird sutiation in that all the main thing that would cause this dont match up, it wasnt the rings, in a sense that they hadent bedded in, i ran 5-600 k's with stock carby, and it had heaps of comp before going. also it doesnt seem like it was caused by detonation, because the way i see it if it was detonating that bad to break the lands and not the rings, then there would be damage on the piston tops....also the rings like i said werent damaged. the reason jeff says its the reason he did is beacuae when the car came on boost it trailed massive amounts of black smoke, i cant see it being lean with the amount of smoke???
i know everyone says efi is the best way to go and it is, but i really wnna get this setup to work properly, the lotus' used the same setup and theres no way they wouldve run them for the amount of years they did with them running like ####. sux because even people that know the lotus setup tell u its exactly ther same sept for the mods ive done so must have something to do with the combination of parts i have inside the carbs ......... oooohhh the fun continues

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I must have missed the part where you said the rings were OK. I assumed they had broken and then cracked the headlands.

but I disagree about the lack of damage to the piston tops -you did say the headland were broken! factory A series pistons don't stand up well under boost. it doesn't take much detonation at all to crack them.


what have you done to the dissy?

how much boost?

what CR?

l18b110, Quote:
when i said the lands were broken i shouldve specified, the lands were broken below the first ring and below the seond ring ill take a photo.
dizzy is electronic stock a15 import one, has been regraphed to i dunno what specs as i dunno what they do.... jeff says its regraphed for turbo but i dunno what that means. i didnt have vac avance conectted to manifold. boost was only 7psi, comp ratio was around 8-8.5 to one, again this is what i was told by jeff taylor as i dont know how to check.... although a fair amount has been removed form the piston so i belive it would be around that.no further material than the stock depth was removed only the dish was made a larger diameter pics below.


ok this pic shows the lands where theyre broken, notice theres no yellow or white spots to show white hot lean out.... only thing that worries me is the scuff marks on the skirt i dont know whther i did this when taking it out or whther there is tighter clearance there, maybe the lands caught the bore? surely rings would go before that happened???


the small crack looking thing on the left isnt a crack is just dirty part or something. notice theres no damage only a few tiny little pin-dot marks from detonation ( i was told thats what it is) theres also no spots that would show lean out. the sides above the rings of the piston are completely black same as this.