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Old 07-25-2007, 02:32 AM   #1
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Default Hey JasonC question about high rpm knock

I got a few weird knock events at high rpm in the link (96-97 obiwan). I am running a 99 head, 8.5:1 compression and 18 psi from a T04E .50.

I got some knock in the 7000-7500 rpm range. Was this due to spark scatter? My timing curve was not very aggressive above 6500 so I don't see why it had a knock event.

I saw one of your old threads on FM about Link suffering from spark scatter and that this could manifest as knock at high rpms. Any further comments?
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Old 07-25-2007, 03:48 AM   #2
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Add race gas. If knock goes away, it was knock.
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Old 07-25-2007, 12:34 PM   #3
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hmmmm... what about just a quart of toluene
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Old 07-25-2007, 03:34 PM   #4
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P.S. It's probably not knock because at such high rpm the motor is least susceptible to knock (lower VE, less time that the mixture sits and detonates while waiting for the spark).

The Link uses a highpass filter for its knock sensor and not a bandpass filter, so it's not that good at differentiating knock from normal noise.

You can see how much spark jitter (scatter) you actually have by setting timing to all 10 then taking a timing light and revving the motor up and down.

A weak ignition can contribute to knock (partially unburned mixture left behind tends to detonate), but I've heard conflicting reports that the stock ignition is adequate at such high power.
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Old 07-25-2007, 04:30 PM   #5
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And the thing is that I have gotten such behavior before from high rpm use when I was trying to autotune the 12 psi range on the old turbo with not particularly aggressive timing settings (close to default) and I got knock readings up around 7000.

Last edited by beerslurpy; 07-25-2007 at 05:57 PM. Reason: spelling
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