Quote:
Originally Posted by steve shadows
Hi Chris
We use active knock detection such as Det cans and we have a knock box but I have never heard knock before reaching correct timing in each cell and achieving knock...at least yet on a Nissan motor.
This is an AGE old tuning debate that was actually discussed even this weekend at the EFI University session we had with Seth from EFI University. Seth backed up my same opinion on tuning off MBT and not being sole focused on knock precautions. Most knock sensors are not even properly configured for the motors they are running on and most oem knock sensors are not designed to pick up the minor knock you are mentioning.
It might also be good to note here that knock IS NOT detonation / extreme engine pressure or typical preignition referred to by most people referring to it...Knock is also not flame fronts meeting in the center of the quench zone of the combustion chamber...
Knock is literally the sound waves of the air inside of the combustion chamber reaching such a pitch and velocity that they explode the fuel air mixture milliseconds prior to TDC during a piston stroke. This vibration is what will actually damage your internals. And also note that on most nissan motors inaudible knock will first start to effect ROD bearings, not pistons in most cases. This is another misnomer.
I think you present an excellent point in that MBT will not always tell you if a motor is tuned in a way to avoid all knock. However tuning with det cans or after market knock senors is an even more risky way to tune off of, based on the fact that most aftermarket knock sensors are extremely hard to properly calibrate due to each individual engine having a different voltage threshold to properly identify actual engine knock and not some other vibration or cam noise in the engine.
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Steve, I agree with you that tuning to MBT is a safer and really, a better way to tune a engine IF that engine reaches MBT before it's knock threshold. That being said, many of the vehicles we tune at our shop reach their knock limit before or very close to MBT, and I am not referring to SR20's. This is why when I tune vehicles, I do both, watch torque and monitor/listen for knock, I'm sure you do the same.
As a side note, many of the late model european turbo cars that come through our shop, straight of the dealer lot, knock. The knock control systems on those vehicles are apparently good enough that the manufactures feel comfortable to calibrate them that way. As an example, we had a brand new Porsche Cayman that was consistently pulling up to four degrees of timing. With the engine cover removed ( the car is mid engine so the engine cover is right behind your head) you could drive it around and hear the engine momentary knock at times as you rolled into the throttle. It was not very loud, but it was definitely there.
- Chris