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Recognizing Knock vs Noise

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Hello,

I have been road tuning my gt86 with a built motor + harrop tvs supercharger + motec m150. Motor has 11.5:1 CR, forged pistons and stiffer valve springs as well as stg3 piper cams. I am finding it hard to believe that at the 7-8 psi boost level I am running on premium pump gas (US 91 oct) that the motor is knocking at 10-12 deg of ign advance through the rev range during a WOT pull. The motor was running up to 27 deg of ign advance at WOT when it was tuned in NA form. I see the knock readings really increase whenever going into boost. Am I just seeing a lot of noise or is this real knock (attached a screenshot of 10-12 deg vs 5.5-7.5 deg ign timing).

P.S. I have calibrated the knock system as outlined in the webinar on knock control in an m150. Also found 15,500 Hz to be the freq that delivers the strongest knock signal when intentionally inducing knock at low rpm + 101kpa MAP.

Thank you for any guidance on this as I am afraid to continue to advance the ign timing if I don't full understand what is going on with these knock readings.

Attached Files
  • kev-05-knock-levels-wot-11-vs-6-ignAdv.jpg
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have you tried conforming the knock events with audio?

What are your intake temps as you may find that it is actually real knock your picking up, from the look of your log I'd be trying to add a little extra fuel to cylinder 1 to try and dampen down the raised activity on the knock sensor on your retarded map

@Chris250, intake temps are 22-25 C. I have not confirmed the knock with audio. Going to do that next.

You really need to get some audio knock gear on there. You need to be able to hear to verify it IMO. Knock is very easy to hear once you know what you're listening for. There are a few youtube videos showing the sound.

To give you some comparison I've tuned probably a dozen 86's now running on the Bullet supercharger system and a stock engine both on MoTeC and the factory ECU via EcuTek and on our local 98 octane fuel I generally find that I'm in the region of 20-23 degrees advance by 7500 rpm. Something doesn't sound right if you can only get 10-12 degrees into the engine without knock occurring. I'm not 100% sure how your 91 octane compares to our 98 though so it's not comparing apples with apples. Your lower CR of 11.5:1 however should be a help here.

I'd back up what's already been said about confirming the knock events with audio knock detection. In our own development car I've put a lot of work into accurately calibrating the knock control system in the M1. I've actually found that 2 cylinders tend to provide a better signal to noise ratio with a slightly different centre frequency to the others so I'm using frequencies of 13,500 Hz, 13600 Hz, 13,700 Hz and 13,800 Hz.

The only other aspect that could be a consideration is your cams and cam timing. I've only ever run the stock cams in these motors so your aftermarket cams may be part of the issue. I'd be very surprised for example if the optimal intake cam position is really 32 deg at 6800 rpm. With stock cams on the Bullet kit you're going to want to be down around 15-20 deg at this rpm.

If you haven't added your own IAT sensor then the M1 will be taking IAT from the MAF sensor which is pre supercharger and hence isn't a realistic IAT value for what the engine is actually seeing.

Your screen shot of the 5.5 deg pull also suggests that you need to adjust the gain for cylinder 1 at least to bring the average signal level in line with the others.

@Andre

I noticed in some of your webinars that you are at around 16 deg of ign timing on pump gas for the turbo'd gt86. Why is your bullet supercharger tune able to run so much more ignition timing (20-23 deg)? Is this a factor of turbo (heat and back pressure) vs supercharger?

Thanks!