Knock Reference and False Knock when tuning a Polaris RZR

Follow

Question:

"When tuning on a Polaris RZR turbo engine, what is the max safe Knock Reference Level? As I see it will always read some amount under a load. I was wondering at what point there is actual detonation occurring? Also in other applications it would show up in a distinct “saw tooth” pattern so you could tell the difference between it and false knock. Is this the same for the Polaris?"

Answer:

There is no “saw tooth” pattern with a piezoelectric knock sensor since it’s basically a microphone. There is always noise as the customer has seen, but the sensor only reads during the timing window for when knock could be occurring on a cylinder (these tables are in Power Core). If there is noise at the frequency it’s looking for during that timing window, then it lets the ECU decide if it should pull timing or not. At that point, the “Knock Control” table is referenced to see how much timing advance should be removed.

 So you can’t just look for a specific reference level since it matters very much when it occurred.  It is also possible to get “false knock” if there is any other noise that happens to occur during the timing window and has a frequency that matches what the knock sensor is tuned to listen for. Rattling heat shields, exhaust rattles, etc etc can all cause false knock at times. The only way a calibrator would know for sure if knock is “false” would be to use a set of Det cans, or fill the vehicle with a high enough octane that it’s not possible for knock to occur and see what the ECU reports.

Also, a log cannot capture every event since we log at about 16-20 hz. If we call it 20 hz, that’s 20 samples per second. At 9000 RPM on a 2 cylinder engine,  there are 150 combustions  per second… which means we can’t capture everything while logging and the ECU is too busy running the engine to send us data at anywhere near that speed.

Was this article helpful?
0 out of 0 found this helpful

Comments

0 comments

Please sign in to leave a comment.