Hi all, now have the new motor in. I bought the ACL forged 8.5comp pistons, cometic head gasket. It is still detonating on 10psi with timing at about 10deg ptdc, it is fine @7deg but too slugish. Also have colder plugs 7 series, might have to use the 8 series plugs. Am using good fuel too. Before rebuild it would run 15psi @15deg without a prob with the standard 6 series plugs. Obviously the real fix is computer, bigger injectors, and a good tune, but does anyone have any thoughts?

definitely a big issue there.. theres no reason as to why you cant run simlar psi on the new motor.. id say chagne your plugs back to standard vlt spec and go from there.. i dont see why you would need a new computer etc.. Best thing is to check whats wrong with it on a dyno.. My guess is dodgey batch of fuel....

It had the standard plugs in about a week ago, I only just changed them. They did allow me to advance the timing a little bit. There has been alot of rain around most likely a bit of watery fuel.

Did you raise or lower the compression from the previous setup, i'm assuming you raised it? Without knowing your setup, i'll assume it's fairly mild: IE T3, front mount, 3" etc. With that sort of setup around 10 deg would be the ballpark max you could run at that compression and boost with the standard computer. The real problem with the factory computer is you're trimming timing out of the whole map, mostly where it's not needed, to cure detonation in certain areas. As above though it could be bad fuel, but to be honest I wouldn't expect to run much more than 10deg advance (probably less) with the factory ecu. As above though i've assumed a lot about your setup, could definitely be some other reason.

has a stage 2 cam, and turbo has a large t4 front housing and wheel. Yes raised comp from standard 7.8 to 8.5 I had it on the dyno at south coast rotary (kevin webbs) dyno before the rebuild and it put out 298hp @ the wheels on 13.3psi with the clutch slipping.

Would be good to know what the real injector pressure is across the load range, good dyno shops should be able to datalog that ? Definitely dont need a new computer yet for that setup, best to diagnose issues before changing too many things at once, edit: If this is the stock VLT ECU then it has fairly well relaxed timing and is already quite conservative, if however you are running an N/A computer and done the workaround to make it run with VLT injectors then it will be a problem..!

any possiblity of a fuel system issue? blocked injectors or poor performing pumps?