Knock Safety by M-Engineering

Hello everyone!  We'd like to start a short and sweet weekly Tech Tuesday article where we can highlight custom features we integrate into the OEM McLaren ECU, Calibration related questions, or just general technical discussions based on what piques your interest.  Since we specialize in software and engine calibration that will generally be the main focus of these discussions.  However, over the past two years of setting world records, iterating calibrations based on experiences, and listening to the wants of our customers we've learned a great deal about the mechanical side as well.

For our first Tech Tuesday we will be discussing:

Knock Safety by M-Engineering

• Why it's useful?
  • Plain and simple it can save a motor from catastrophic failure from cylinder pressures being too high.  Increasing engine torque and power output is generally done by increasing cylinder pressures.  Knock can create drastic spikes in cylinder pressure in very short amounts of time.  High levels of knock under high load / high cylinder pressures are typically what cause engine damage.  That engine damage can come in all shapes and sizes.  By monitoring knock levels we can close the throttle if dangerous levels of knock are present, potentially saving the motor from catastrophic damage and alerting the driver to a potential issue.  For the sake of brevity we will not discuss what knock is in this short article.  If there is interest in that topic let us know and we can discuss it in a future Tech Tuesday!
• What does it do?
  • The Knock Engine Safety is custom logic we've written and integrated into the OEM ECU to monitor knock corrections every hundredth of a second (100Hz) and drastically lowers load / boost / throttle if dangerous levels of knock are detected.
• How it works?
  • There are two separate ways a knock safety can be triggered.
    • large singular knock event in any one cylinder
      or
    • multiple smaller knock events across multiple cylinders
  • Since cylinder pressures will change based on boost, ignition advance, charge temp, etc... Each map slot has a calibratable knock threshold.  Map slots with a higher base cylinder pressure under WOT (e.g. higher octane, more boost, etc...) will have a decreased threshold and are more likely to trigger a safety if knock is present.
• What happens when a knock safety is triggered?
  • The load is drastically reduced and the throttle is closed
    • We chose a load level where you can still safely navigate traffic if the safety occurs.
    • After 10 seconds of low throttle pedal input the safety will reset and allow for full throttle again
• Why do we implement it in all our McLaren calibrations?
  • Every situation is different.  What we mean by that is McLarens come in all conditions. We advise that you're up to date on all routine maintenance, keep close tabs on your oil level, and decrease your oil service intervals, but we also try to mitigate as much risk as possible when you choose to tune your car.  We do this with heavily vetted calibrations as a starting point, however mechanical issues can and do arise.  When an issue is encountered on one of our calibrations we can generally attribute to a situational cause rather than the calibration itself.  Our most common situations for a knock sensor being triggered are from bad gas or improper map slot for the situation.  Improper map slot refers to an end user running a map slot that is more aggressive and designed for higher octane, with a lower octane fuel in the tank.

To better illustrate Knock Safeties here is a break down of the calibratable knock safety tables in M-Composer that were used in a Stage3 McLaren 570S on E85 that recently made 850whp.

The example will instantly trigger a knock safety if any single cylinder hits -10* or if 3 or more cylinders hit -2* or more of correction. 10 seconds is the cooldown time needed after an engine safety is tripped to allow full throttle operation again. And load will need to be above 100 for the knock safeties to be active. For reference, a stock McLaren 720S with a stock calibration will pull -6 to -8 degrees of timing routinely under heavy load on the super crummy 91 octane fuel found in California.

Knock Safety is just one of many custom engine safeties that M-Engineering has written and integrated into the OEM McLaren ECU all in an effort to give our end users the fastest, safest, and most reliable calibration on the market!

Thanks everyone for reading, we hope you find these informative! Engagement and questions will motivate us to keep this series going. Since this is the first Tech Tuesday any input is welcomed!

More info can always be found at www.M-Engineering.us or by emailing us at info@M-Engineering.us

- M-Engineering Crew