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Old 10-24-2003, 07:18 PM   #1
Hole-Shot
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Default Knock sensor…Could loud exhaust trigger it?

Are all knock sensors created equal? Are there variations from the L98 to LT1 to LT4?

Is it possible to trigger the knock sensor with loud exhaust? (my exhaust is VERY loud, headers into true duals, into straight through 12” resonators.)

If I run my timing @6 btdc I get ~10 degrees of timing retard and dozens of knock counts. If I retard my timing to 0 degrees BTDC I get a lot less knock counts and little to no spark retard.

I do not hear any pinging or knock from the motor. :confused:
I guess that I just need some input on this.

Thanks for your help.
:cheers:
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Old 10-24-2003, 08:46 PM   #2
95AquaC4
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Default Re: Knock sensorÂ…Could loud exhaust trigger it? (Hole-Shot)

I was told that it could. When we go test and tune, we never know who we're lining up against. I go sometimes with a guy with a AA modified that runs 7's. (extremely loud exhaust)We were lined up together, but at the last minute the starter sent him and I seperate. I asked why, and this was one of the reasons that was explained to me.


[Modified by 95AquaC4, 8:46 PM 10/24/2003]
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Old 10-24-2003, 08:52 PM   #3
Hole-Shot
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Default Re: Knock sensor…Could loud exhaust trigger it? (95AquaC4)

Quote:
I was told that it could. When we go test and tune, we never know who we're lining up against. I go sometimes with a guy with a AA modified that runs 7's. (extremely loud exhaust)We were lined up together, but at the last minute the starter sent him and I seperate. I asked why, and this was one of the reasons that was explained to me.
Hmmm… interesting.

I should add that I just replaced my knock sensor and I didn’t get as much knock/retard with the old sensor. Maybe I will put that one back in and hook up the Diacom to it and see where things land.


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Old 10-24-2003, 09:14 PM   #4
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Default Re: Knock sensor…Could loud exhaust trigger it? (Hole-Shot)

You can wrap teflon tape on them to desensitize them, but at the risk of engine damage though....Torque of the sensor is another reason for sensitivity as well so only tighten them to spec.

LT4 has a knock module designed for them because of timing chain, roller rocker and other noise issues that give "false" knock.

You could add some octane booster to see if the "knock retard" goes down or away. Then you may know that you are actually detonating instead of getting header noise involved.
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Old 10-24-2003, 11:33 PM   #5
pablocruise
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Default Re: Knock sensorÂ…Could loud exhaust trigger it? (Hole-Shot)

I have headers into true duals into flowmaster 3 chambers and my EASE diagnostic software showed no knock counts(this at 6*)
I understand by the time knock is audible, it had been going on way before.
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Old 10-25-2003, 12:35 PM   #6
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Default Re: Knock sensor…Could loud exhaust trigger it? (Goody)

Quote:
You could add some octane booster to see if the "knock retard" goes down or away. Then you may know that you are actually detonating instead of getting header noise involved.
Right now i am running high octane additives in the gas.

Maybe the LT4 knock sensor is worth trying.
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Old 10-25-2003, 05:38 PM   #7
REDZ28
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Default Re: Knock sensor…Co uld loud exhaust trigger it? (Hole-Shot)

What Kinda fuel you running? That video you have of your car running last year shows it detonating. You need very good fuel for your motor. As you know I know the guy who buily it. He used to use Toluene in the fuel so it wouldnt detonate(cause knock retard).
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Old 10-25-2003, 07:51 PM   #8
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Default Re: Knock sensor…Could loud exhaust trigger it? (REDZ28)

Quote:
What Kinda fuel you running?
RedZ28,

I always run 100 octane unleaded race gas in the car when I am at the track. Otherwise I run the same formula of toluene that Lasiter ran/recommended. In regards to that video clip, when you see that puff of black, it actually threw a code 15 at that point and put the car in limp home mode. I seen the SES light come on and it really coincides with where I was on the track. So, no it was not detonation. I am extremely careful when it comes to those types of issues. I checked the code immediately after getting back to the pits. After I limped back home, I changed the sensor and everything was fine once again.
:thumbs:




[Modified by Hole-Shot, 7:51 PM 10/25/2003]
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Old 10-26-2003, 12:32 AM   #9
88_vette
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Default Re: Knock sensor…Could loud exhaust trigger it? (Hole-Shot)

Yes your exhaust can cause issues with the knock sensor, finding out that it is the exhaust is not easy. I found my car after mods would have reports of knock around 3,000RPM with just reving no load. upon heavy research found these to be false.
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Old 10-26-2003, 12:36 AM   #10
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Default Re: Knock sensor…Could loud exhaust trigger it? (88_vette)

Hmm...I wonder if my new exhaust might cause false knock counts...(Hooker 2149's into Dual Mandrel Bent 2½" Piping, Into a Center 3" Dynomax Race Bullet, back out to dual 2½" Mandrel Bent Piping)
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Old 10-26-2003, 09:07 AM   #11
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Default Re: Knock sensorÂ…Could loud exhaust trigger it? (Hole-Shot)

Yes. I've done lots of research/testing with knock sensors.

We have a late model stock car with 4" open exhaust and all racing goodies in the engine, etc. We installed a couple of GM knock sensors and circuitry connected to a dash light. With the car in neutral, certain RPMs cause just the right resonance to trigger the sensor, but definitely no detonation. Also, cranking the engine triggers it, and if you lightly tap the chassis/engine with a hammer, etc. Under load in a race we don't see it on, unless the engine detonates.

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Old 10-26-2003, 09:07 AM
 
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