Can some explain *knock*
Thread Starter
Joined: Mar 2002
Posts: 5,778
Likes: 4
From: SW Chicago, IL
Can some explain *knock* I think I somewhat know what it is, but I would love to get a basic explaination so I would understand it better. How does it effect the car, How is it caused ect... 
TECH Fanatic
Joined: Nov 2002
Posts: 1,248
Likes: 0
From: Oklahoma
Re: Can some explain *knock* Knock is simple: Detonation before the spark.
The computer detects knock, and retards timing to make it go away, robbing HP. You will probably notice knock if youve done a lot of air mods, and havent given it more fuel. Also, extreme heat will blow the mixture prematurely, hence the 160* thermostats and whatnot.
If you have done a lot of air mods, and dont want to go for LS1 Edit just yet, grab a MAF translator. It lets you ritchen (or lean) your mix back to normal. Also, try running 93+ octane gas instead of 87 if you are, it requires more heat/pressure to detonate it, reducing knock (sometimes).
If you are getting 3.9* of knock retard at all times, join the "3.9 KR club". Some LS1s suffer from this, and I am not for sure if anyones figured out why.
I got my knock sensors wet from washing my engine, and had to pull the intake manifold to replace them. (I wouldnt wish this on my worst enemy.)
Knock = Bad
The computer detects knock, and retards timing to make it go away, robbing HP. You will probably notice knock if youve done a lot of air mods, and havent given it more fuel. Also, extreme heat will blow the mixture prematurely, hence the 160* thermostats and whatnot.
If you have done a lot of air mods, and dont want to go for LS1 Edit just yet, grab a MAF translator. It lets you ritchen (or lean) your mix back to normal. Also, try running 93+ octane gas instead of 87 if you are, it requires more heat/pressure to detonate it, reducing knock (sometimes).
If you are getting 3.9* of knock retard at all times, join the "3.9 KR club". Some LS1s suffer from this, and I am not for sure if anyones figured out why.
I got my knock sensors wet from washing my engine, and had to pull the intake manifold to replace them. (I wouldnt wish this on my worst enemy.)Knock = Bad
TECH Enthusiast
Joined: Aug 2002
Posts: 585
Likes: 0
From: CLARKSVILLE,TN
Re: Can some explain *knock* Just to add a little more from a mechanical stand point. Normally When the piston gets to the top of the cylinder and the fuel is compressed the spark plug fires and the pressure forces the piston back down. The trick is that the fire burns at one speed and the engine runs at different speeds so you have to make the spark happen actually before the piston gets all the way to the top when the engine revs up. If you don't it'll fire too late and you won't make nearly as much pressure in the cylinder. Detonation happens when you get fire (pressure) too soon and it pushes down against the still upward bound piston. When the knock sensor hears that going it simply slows the spark and you end up with the not enough pressure thing happening which will cost you mucho power. So the object is to run the advance right on the edge without pinging. 
Thread Starter
Joined: Mar 2002
Posts: 5,778
Likes: 4
From: SW Chicago, IL
Re: Can some explain *knock* Thanks guys!
I personally don't think my car has any knock, or enough to affect it majorly. But I was reading up on knock and didn't exactly know what it did. But now I do somewhat do
.
Another reason I was asking is because some guy in a talon ran a best of 13.1 at RT66 and said he could do better but his knock is around 25... and said that it was too cold outside which is why he had it (60 out yesterday). He was saying that he runs best in 70-75 degree weather because his knock goes down... so I'm guessing that his spark happens to late instead of too soon?
I personally don't think my car has any knock, or enough to affect it majorly. But I was reading up on knock and didn't exactly know what it did. But now I do somewhat do
. Another reason I was asking is because some guy in a talon ran a best of 13.1 at RT66 and said he could do better but his knock is around 25... and said that it was too cold outside which is why he had it (60 out yesterday). He was saying that he runs best in 70-75 degree weather because his knock goes down... so I'm guessing that his spark happens to late instead of too soon?
Re: Can some explain *knock* Actually it's the other way around, you have less problems with engine knock with a cool engine. That's one reason some people put in a 160 T-stat. The cool air also gives the engine more power by increasing the density of the fuel-air mixture. The best way to control knock is by retarding the timing until it goes away.
Thread Starter
Joined: Mar 2002
Posts: 5,778
Likes: 4
From: SW Chicago, IL
Re: Can some explain *knock*
Actually it's the other way around, you have less problems with engine knock with a cool engine. That's one reason some people put in a 160 T-stat. The cool air also gives the engine more power by increasing the density of the fuel-air mixture. The best way to control knock is by retarding the timing until it goes away.
Teching In
Joined: Oct 2002
Posts: 24
Likes: 0
From: west palm beach, fl.
Re: Can some explain *knock* I'll throw in a gallon or 2 of 100 octane at the track on really hot summer nights to quite down the knock. Usually works. No problems with knock in the winter.
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Teching In
Joined: Oct 2002
Posts: 24
Likes: 0
From: west palm beach, fl.
Re: Can some explain *knock* On hot summer racing days, I'll throw in a gallon or two of 100 octane along with the 93 octane in the tank. This will only raise the total octane 1-2 points, but it's usually enough to quiet things down.
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