the engine was run in with stock carby and extractors for over 400 k's only then did i put the turbine on, anyways it was only 7psi i think this time around it was the tune that was to blame. i comp tested it this arvo and one cyl is down at about 80-90psi the restare hovering around 130 maybe have a set of cracked ring or a broken piston.... hmm wateva it is looks like im going to have to have a look inside. more updates next week maybe.

Look on the positive side. The head gasket could be leaking into the push rod holes.
Either that or it could be a broken ring land. Did the machinest give your bores a bit of extra clearance to allow for your pistons to grow a bit more due to your running boost?
Which cylinder was down?

maybe your right if it was leaking into pushrod hole could it be down on comp? it wasthe third cylinder.

hey guys another a15 turbo update, i pulled my motor apart tonight and it all looked perfect, bearings had not a score, they hardly looked used, the bores were the same, as for the crank bearing surfaces. i then got to the pistons, and i pulled em all and looked at no3 and it looked like it had a crack i wiped it clean and then took the rings out, whilst doing this i knocked out two broken ring lands...... i wonder what caused it ?? i got the engine hot at one stage, (no coolant) but i ran it after that and it held 135 psi across all four a few days after running hot.. maybe the slight amount of detonation i had is wat killed it??? ohh well looks like off to jeffs for another piston at least, and new rings bearing and gaskets. this time im gonna save up heaps of extra to get it done properly, ie tune, exhaust, engineering and that.

Maybe because fuel blew out the carbies and it ran lean and detonated. Detonation is actually happening and doing damage even before it can be heard. If you can hear it, its already doing its work.

Most people beginning to experiment with blowthrough, always seem to overlook the fuel leaking from their carbie.
Its the most important thing. Think about how much fuel you saw leaking and then think about how much fuel a carbie actually supplies to an engine.
A really lean mixture still burns. It actually burns hotter than a stoich mixture. Being hotter it makes the engine produce more power and appear to be running excellent.
Lean mixtures turn spark plugs white. For something to heat up and turn white, it is really past hot and beginning to burn. Now think about the rest of the combustion chamber.

Dont over look your leaking carbies.

i see where ur coming from but the mixture was never lean the spark plugs were never white or even close to brown, the exhaust is so badly blackened with soot, and the amount of fuel coming out was about a drop or so after driving for an hour or two, the fuel only just ran down the fuel bowl onto the carby body so was #### all fuel. im not saying it wasnt that it was running lean but surely if it was, the plugs would show a sign..... ohh well at least one thing came out of it, next time i know to not drive it when its out of tune like this time, i am going in search of a dyno tuner, ive heard mick's motorsport at milperra can dyno dellorto's, he has australia's fastest n/a gemini it runs webers so i think ill give him a call.

The engine actually runs on less fuel than you would call a carbie leak. Thats the whole thing - go start you engine you have running and look directly down the carbie and make note of how much fuel is actually being used.
An engine can be tuned to run pig rich enough to make everything black. When the engine was detonating did you turn it off and never run it there after? You have an engine that runs rich most of the time and under boost detonates. Its not like you have an engine that runs lean all the time and at service time you can check the plugs.

I am not saying fuel leaking is your only demon. Ignition timing could of been crap. Intake temps could of been crap.
But dont think the leaking fuel is nothing.
Fuel evaporates in hot environments.

Like the good Dokta said, Take it for a strap and shut it down at full noise(a "plug chop"), not a real good expierience for the turbo bushes, but still a better way to examine the plugs. Also a bit hard with the engine apart.

Another thing to inspect is the exhaust valves. When the engine runs lean, it creates a lot of heat, the exhaust valves copping a lot of it. How are they looking?

On the dyno with a sniffer is the safest bet.

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yep, it was caused by detonation. you used black rings, didn't you? on a boosted engine it doesn't take too much detonation to crack them, then the broken pieces work against each other. sometimes they can overlap and crack the piston's headland.

as for what caused the detonation, when an engine is running hot, it will be prone to detonating for sure. It may just have been that, and it took a bit of time before the broken rings actually caused the problem.


Otherwise, as phunk said, its either leaning out under boost, or running too much timing (what have you done to control the advance?), or it could be caused by a hot spot in a combustion chamber - have you done any work to them? sharp edges can cause hot spots, but so can carbon build up.

mmm turbo territory...still scares me...