//scottInSoCal

Anyone know the story on engine knock? I am curious about when and if it occurs (stock and/or chipped). Also, has anyone done any modifications to counter knock - by default, the ECU probably retards the timing. I have a buddy who is a diehard Buick turbo fan, and he has an alcohol injection kit on his car that is activated by the knock sensor (timing is almost never affected by knock with this kit installed). I realize this may be a little overboard for an S4 (which is by no means a drag racer). Any feedback is appreciated. Thanks,

TRM

Please chime in experts: Knock is basically pre-detonation of the air fuel charge before the cylinder has reached Top-Dead-Center? I could be off. But it is a common term for Detonation.

It's bad! It does really nasty things to the valves and cylinder heads.

With the Nissan 300ZX, basically these kids would run really cheap gas in their chipped 300ZX Twin Turbos. Low Octane Fuel, 1.1 Bar of Boost and Hot Temperatures on Drag Days do not mix.

If the knock sensor was not working properly, they would have problems because they would retain full boost and get detonation. You can hear it too. Typically it sounds like a ball bearing rattling around in a coffee can.

I assume the S4 has a decent knock sensor and would bump you into saftey boost or limp mode if knock was occuring.

NASA racer

this can be very subtle...the car just doesn't make full power. With a chipped car it can be dramatic and lead to hesitation as the ECU quickly cuts timing then adds it then cuts it.

You should never hear knock in your engine but that doesn't mean that you aren't getting preignition.

The cylinder temperatures/pressures of a turbo engine mean at ALL TIMES you need the highest octane you can possibly get...this is even MORE important for a chipped S4.

//scottInSoCal

That is what I figured. My question now is, if I use 93+ octane with stock IC's and the air temp is say 90degF - will my engine get to the point, under hard acceleration, where it is susceptible to knocking? I am wondering if some means of knock reduction is worth exploring.