Hey all,

About half of my datalogs show 1 knock sum between 6000-7500 rpm's, but it's not always at the same rpm. It also doesn't always last the same amount of time. Sometimes it will last for 500 rpm's, sometimes for only 100 rpm's. It will sometimes pull 1 degree of timing because of this, but not always. Is this something I should get rid of? I've already dropped timing by 3-4 degrees in those load cells versus stock (and this is on a stock GSR with 91 octane). Should I drop timing some more?

The main reason I'm hesitant to pull more timing is because the knock is not consistent (I can't seem to get it to occur at the same rpm/load in back to back data logs of various gears). What do you all think? Should I tune for 0 knock?

 

Depends on you knock tolerance. I typically allow 2-8 counts of knock. That is COUNTS not degrees

Maybe instead of pulling timing, why don't you try adding a touch of fuel?

 

It's already running 11.0 AFR or even slightly richer sometimes at high rpm When you say you allow 2-8 counts of knock, do you mean up to 8 at one specific rpm? For example, if the knock sum stays at 1 from 6200 through 6700 rpm's, is that still considered just 1 knock sum? Thanks!

 

Yes, that is 1 knock sum. I wouldn't allow it to stay at 8 counts for long but a quick little spike, I don't worry about to much...If you start seeing 15-20 counts, you need to back off. There is such a thing as rich knock but I don't think that could be the case at 11:1

I don't know if a consensus on the allowable amount of knock has been talked about for the X specifically...most tuners(home tuners) like to shoot for just a hair of knock, some play it extra safe with no knock.

I tuned my previous eclipse (500hp) with 5-7 counts of knock at higher rpm's, and she ran for over 2 years until I sold her

 

its nothing 1 knock sum dont worry about it

 

1 is fine.

 

Thanks guys! I'll stop driving myself crazy trying to tune this out

 

It also depends on the heat of the combustion chamber/pistons. When heat rises the pistons expand and the clearance gets tighter (less chance of knock). The colder it is, the more the clearance and the more chances of knock. Don't do WOT runs when the engine is cold.

In my case, I allow 1-3 counts of knock.

 

1 is fine.

occasional/random 2 is ok

 

Thanks all! While we're on the topic, has anyone noticed random knock in low rpms? I seem to get it a lot when starting from a stop. Anywhere from 1000-2500 rpm's, I'll sometimes get up to 6 knock sum on a completely stock car with stock timing down low. It's very random, and happens maybe 20% of the time. Most of the time it's just 1-3 knock sum though.

 

^Ive seen that low rpm knock as well. I chalked it up to a noisy engine and perhaps the knock sensor picking up the clunking from the clutch? When i saw it last i was driving normally and shifting from 1st - 2nd and in closed loop.

I also have knock sum of 1 from about 3200 - 3600 rpm that i was about to try and start tuning out. I was making the assumption that the knock sum was per collection interval / load cell (this is all using Tephras mode23 logger btw). I've been holding off however since I started thinking "well its a SUM not a count so maybe i'm ok". Looks like based on the above the knock occurs at the load cell that its first reported at, then sticks around until that knock count is reset.


How often does that knock sum reset?


Thanks

 

There is no knock learning. There is Octane Percent that will drop from 100% depending on amount of knock, and more importantly, the duration. A drop from 100% will start interpolating between the High and Low octane maps.

One thing to note is that this % quickly resets. You let off, drive a little, get on it again, octane will be at 100% again until an event drops it again.

 

Thanks for the info! Have you ever seen timing drop lower than your maps specify even though there is no significant knock? Sometimes I've noticed the car seems to be running a couple of degrees less than the high octane timing map specifies, but I don't have any knock greater than 1-2 occasional hits. I haven't continuously logged octane level but anytime I did check it, I saw 100. Maybe I need to log octane level more.

 

There are other timing compensation maps that can come into play, like low/high intake temps, coolant temps, etc

-bryan

 

Bryan, thanks once again for reminding me of these things I was just reading all of this in the service manual last week, but perhaps I've been looking at too many datalogs lately to remember anything