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Hi Andre I have a concerned about using 93 octane (98ron) pump gas tuning cars,
for some reason it seems no matter how much time i spend on dyno making sure it is knock free. I will always get occasional knock on every car for example my evo on pump gas would always randomly knock once or twice a week with knock sum of 6 or 7,
And Subaru would also always randomly get a minus 2.8 on pump. At first I always thought those were false knock because thats what every tuner told me in the past that these cars have very sensitive knock sensor and report false knock all the time.
But as soon as I started playing with e85 a year ago non of my car ever gets those random high knock anymore, so this proofs that all those rare random high knock event in the past was all real.
How can we ensure our tune will never knock on 93 octane (98RON) pump gas or that's just not possible because pump gas octane isn't high enough for every situation?
The Evo engine i am not really too worried since it has forge piston so those rare high knock doesn't concern me much,
however Subaru Fragile piston really worry's me and with Subaru it is very very common to see at least minus 2.8 degrees of knock every 2 days on pump gas if ambient temperature is high like summer time.
I tune on 98 pump gas probably more than any other fuel and it is challenging. The situation you MUST avoid is consistent and repeatable knock under sustained high load driving. If you are continually getting knock under a 2nd-4th gear accelerate pull then revisit your timing map. It isn't uncommon however to still encounter the occasional random knock event and in many cases we probably don need to be too concerned about them.
If possible you really need to log to find out when and under what situations the knock is occurring. If it's heat related then you may be able to address this based on ignition trims. I tend to see knock occasionally if the car hasn't been used under high load for a while (which is pretty typical of a lot of street cars) and then is opened up to WOT. You will quite often see an initial knock event and nothing subsequent.
While I apply a bit of experience to the situation, I'm usually not concerned if I see one random knock event. E chances are that to never log any knock you would need the timing set so conservative,y that you'd be giving away huge chunks of power everywhere. Understand also that this is why the ECU is equipped with a knock control strategy so let it do its job
Is there any way to avoid that knock on the EVO if the car hasn't been used under high load for a while,
for example going wot on 1st gear couple times before going wot on 4th gear?
I find cars are a lot less likely to encounter random knock on 1st and 2nd gear but usually Random knock is always 3rd or 4th gear pull.
Nothing I can specifically think of sorry. I've never really come to any firm conclusions as to exactly what causes this. I've got my theories but they are simply theories.
You're suggestion is probably as good as any I could offer. You find that 1st and 2nd gear don't apply as much load to the engine since it accelerates so quickly through those gears. In all honesty though it's probably less of an issue than you think it is.