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Old 05-04-2015, 01:27 AM   #1
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Default Alcohol/E85 knock detection methods

How is everyone detecting knock?

With just det headphones its really hard to tell, does anyone have some good clear recording as examples?

Is knock windowing accurate with alcohol and good enough?

I have just pulled the head off a car running 11.2:1, 25psi, and 20* timing with no signs of knock, but when I tuned it it was so hard to be sure.

Thanks,
Dann
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Old 05-06-2015, 12:15 AM   #2
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Should I have this moved to race prep or something?
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Old 05-06-2015, 12:57 AM   #3
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It shouldn't be hard to tell unless the car is straightpiped or something. If it's unclear, improve the quality of the headphones or go to a mechanical set (nylon hose from the engine block to your ear).
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Old 05-06-2015, 02:40 AM   #4
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Thanks andrew, Ive never heard knock on alcohol, and all of the more experienced tuners near me claim that its almost impossible to hear, can you point me to any recordings, or does it truly just sound like gasoline?

Thanks,
Dann

EDITED: Used australian terminology

Last edited by nitrodann; 05-06-2015 at 02:55 AM.
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Old 05-06-2015, 05:15 AM   #5
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When you hear knock on e85 it means either a catastrophic failure or that your ethanol sucks.
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Old 05-06-2015, 07:16 AM   #6
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So how do I tune if the engine is knock limited on E85?
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Old 05-07-2015, 12:41 AM   #7
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Quote:
Originally Posted by nitrodann View Post
Thanks andrew, Ive never heard knock on alcohol, and all of the more experienced tuners near me claim that its almost impossible to hear, can you point me to any recordings, or does it truly just sound like gasoline?

Thanks,
Dann

EDITED: Used australian terminology
If it knocks it will sound the same, it will sound the same because knock results in the same thing, hammering the bearings.

As for how to tune it if it's knock limited, I'd say use det cans, with either a dyno, a drag strip, datalogs on a long road, something to compare power to see how much timing helps power.
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Old 05-07-2015, 01:30 PM   #8
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I dont think knock windowing will need to be adjusted, but you should check it to make sure. If you start running spark advance numbers that push outside of your knock window then you're going to have to change it, but you're not going to get there at WOT, just cruise.
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Old 05-08-2015, 10:08 AM   #9
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Quote:
Originally Posted by nitrodann View Post
So how do I tune if the engine is knock limited on E85?
I believe what the previous post meant was not that you can't have a knock limited E85 motor, but such a thing is pretty hard to pull off with a Miata engine.
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Old 05-08-2015, 11:46 AM   #10
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I though that this 11.2 motor running 25psi would be getting close but apparently not.
Can anyone confirm that alcohol knock sounds like normal gas knock?
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Old 05-08-2015, 12:25 PM   #11
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you need like 250F intake temps for E85 to knock
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Old 05-08-2015, 02:36 PM   #12
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It's easy to tune e85, add timing as long it's making more power. When it makes less you are over the limit and very close to knock and engine failure.
Most tuners don't even go this far and that's why they "have not heard knock on e85".
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Old 05-09-2015, 08:54 PM   #13
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New to this engine so have a question. Why so rich on E85 ? Most other cars I have tuned prefer E85 to be run closer to 12:1 for the smoothest power. As you stated, knock is hardly an issue with this fuel.

Harry
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Old 05-10-2015, 12:38 AM   #14
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Quote:
Originally Posted by ztunerz View Post
New to this engine so have a question. Why so rich on E85 ? Most other cars I have tuned prefer E85 to be run closer to 12:1 for the smoothest power. As you stated, knock is hardly an issue with this fuel.

Harry
He is talking about compression ratio not air/fuel.
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Old 05-10-2015, 01:45 AM   #15
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Quote:
Originally Posted by ThunderKunt View Post
He is talking about compression ratio not air/fuel.


Ahh, makes sense now - ty
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