Is One Knock Too Many?
01-02-2009, 10:08 PM
#1
Drifting
Thread Starter
Is One Knock Too Many?
I have been reading the knock counts on my car the past couple of days. I have found counts of 8, 3, 5, 4, 7, intermixed with lots of zeros.
In the past I have never counted even one.
The temperature is much colder now; 20 F yesterday, 32 F today. In the past I've done the counts (a couple of times) in the summer time.
I have tried two different AFMs with similar results. Yesterday the counts were 5, 7, 8 with several zeros. Today with a different AFM (my original unit) they were 3, 5, 4 with several zeros. I tried different driving styles - high rpm, low rpm, heavy load, light load. The knocks seem to be at high load, but the tests were not scientific enough to be sure.
So, my question is, how many knocks are too many?
Is one knock in 10,000 too many?
Thanks,
Dave
In the past I have never counted even one.
The temperature is much colder now; 20 F yesterday, 32 F today. In the past I've done the counts (a couple of times) in the summer time.
I have tried two different AFMs with similar results. Yesterday the counts were 5, 7, 8 with several zeros. Today with a different AFM (my original unit) they were 3, 5, 4 with several zeros. I tried different driving styles - high rpm, low rpm, heavy load, light load. The knocks seem to be at high load, but the tests were not scientific enough to be sure.
So, my question is, how many knocks are too many?
Is one knock in 10,000 too many?
Thanks,
Dave
01-02-2009, 11:28 PM
#2
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I have been logging knock-count runs lately and find that on two 993 turbo cars with extensive mapping show anywhere from 6-12 knock events per 10000. I have been told by tuners that anything under 15 is typical for any car.
01-03-2009, 06:02 PM
#4
Drifting
Thread Starter
http://www2.zhome.com:81/ZCMnL/PICS/...winterGas.html
The above linked reference states that winter fuel formulations actually have higher octane ratings. This would suggest less knocks; no?
What about the denser cold air? Does that mean higher compression ratios, as I would expect? And, therefore, greater knock count?
By the way, I put the other AFM back in today and ran additional knock count tests. I counted 6 a couple of times and 10 once in addition to several counts of 1 and 0. I ran High rpm, Middle rpm and Low rpm. I then ran some high load tests - wot :-) - with High rpm, Middle rpm and Low rpm. The high rpm, high load runs had the high knock counts.
I've also been searching for acceptable knock counts and found that a) turbo folks are very interested in knock and b) that there seems to be no clear consensus on an acceptable knock count, but that 10, or more, is to be expected.
Here are some random quotes:
Ever curious,
Dave
The bottom line is that when it's cold, winter gas seems to be the hot ticket for performance enthusiasts. Not only is the dense winter air good for horsepower, but the higher oxygen content and octane value of winter gas make the pot sweeter
What about the denser cold air? Does that mean higher compression ratios, as I would expect? And, therefore, greater knock count?
By the way, I put the other AFM back in today and ran additional knock count tests. I counted 6 a couple of times and 10 once in addition to several counts of 1 and 0. I ran High rpm, Middle rpm and Low rpm. I then ran some high load tests - wot :-) - with High rpm, Middle rpm and Low rpm. The high rpm, high load runs had the high knock counts.
I've also been searching for acceptable knock counts and found that a) turbo folks are very interested in knock and b) that there seems to be no clear consensus on an acceptable knock count, but that 10, or more, is to be expected.
Here are some random quotes:
Code:
chris walrod:
has been told by tuners that anything under 15 is typical for any car
no retard below 7
10+ is bad
knocks of 5+ msec are noted - knock duration counter vs hit counter
10-20 count is okay
60-70 time to worry
<10 on race gas @ wot
0-7 counts will not retard timing
usually 1-4 counts on a really good hard pulling run at the track
sample DSMLink log data:
1 count raw knock = .4 deg of timing retard
3 count raw knock = 1.1 deg of timing retard
12 count raw knock = 4.2 deg of timing retard
18 count raw knock = 6.4 deg of timing retard
It seems that unlike the 1G ECU, the 2G ECU starts
pulling timing when it see *ANY* knock.
The ECU learns what is considered "acceptable knock" over a period
of time. It then disregards this information as background noise
and establishes a baseline from there. This is constantly
changing as the car ages, mods change, sensors degrade, etc,
etc.
Dave
01-03-2009, 06:09 PM
#5
Nordschleife Master
It is said that winter gas and summer gas is not same same .
As the heat goes up , the need for higher octane grows .
Why they would make higher octane gas for winter ?
As the heat goes up , the need for higher octane grows .
Why they would make higher octane gas for winter ?
01-03-2009, 06:15 PM
#6
Drifting
Thread Starter
The write-up said
Higher octane seems to be a side effect.
I'm not sure it's correct. It's just one internet reference, but it seemed interesting to me.
Too much time on my hands, I suppose.
Back to work on Monday . . .
For reformulated winter gas, lighter, low-boiling-point components are added to the gasoline to increase volatility. This makes your car easier to start and accelerates converter light-off, thus lowering emissions. That's the official line on reformulated gas.
I'm not sure it's correct. It's just one internet reference, but it seemed interesting to me.
Too much time on my hands, I suppose.
Back to work on Monday . . .
