Timing, AFR, Knock
Thread Starter
TECH Resident
Joined: Sep 2009
Posts: 859
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From: Frozen Tundra, WI
Timing, AFR, Knock Will an engine always lean out before it knocks (pre-ignition)??
I am checking because I have read a few posts about how the motor will lean out if when timing is advanced...which makes sense.
If I don't ever let it get leaner than say 14.5:1 (cruise) or 13:1 (wot) then it won't knock??
So...can a wideband = knock sensor (preventer)??
I am checking because I have read a few posts about how the motor will lean out if when timing is advanced...which makes sense.
If I don't ever let it get leaner than say 14.5:1 (cruise) or 13:1 (wot) then it won't knock??
So...can a wideband = knock sensor (preventer)??
TECH Regular
Joined: Jan 2005
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From: Orlaanndoooo
Short answer, no.
It is entirely possible to be on the rich side & still have a combustion chamber hot enough for preignition...or too much timing for the conditions. If you have too much timing for the conditions it will still detonate.
A wide band will only help you see the air-fuel ratio. You need that info along with rpm & manifold absolute pressure and it will help you tailor your fuel curve to your engine.
It is entirely possible to be on the rich side & still have a combustion chamber hot enough for preignition...or too much timing for the conditions. If you have too much timing for the conditions it will still detonate.
A wide band will only help you see the air-fuel ratio. You need that info along with rpm & manifold absolute pressure and it will help you tailor your fuel curve to your engine.
Thread Starter
TECH Resident
Joined: Sep 2009
Posts: 859
Likes: 2
From: Frozen Tundra, WI
Thanks for the reply. I kind of figured that was the case but I was hoping there might be a nice easy way for me to prevent knock since I don't have the sensors (it's carb'd). Oh well...it was worth a shot. 
TECH Senior Member
Joined: Apr 2002
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From: So.Cal.
There are 5 things that can cause knock, and each one can do this independently of the others:
- dynamic compression ratio,
- ignition advance,
- AFR,
- combustion chamber temperature,
- load.
- dynamic compression ratio,
- ignition advance,
- AFR,
- combustion chamber temperature,
- load.
