I am still very new to this ...only a week or two. My collected knowledge and data is still very minimal, so I thought I would post this and see what anybody had to say before I started playing with my actual flash.

I am curious about the knock counts that I get when i get to the rev limiter, and then once I lift off the throttle.

Here is an example from a 3rd gear pull:

RPM...........Knock...Timing......Load
5562.5.......0..........10............216.41
5718.75.....0..........11............218.81
5843.75.....0..........12............217.62
5968.75.....0..........13............210.52
6093.75.....0..........14............209.39
6218.75.....0..........15............205.86
6375..........0..........17............201.25
6468.75.....0..........17............197.74
6625..........0..........18............197.74
6718.75.....0..........20............193.19
6843.75.....0..........21............189.7
6968.75.....0..........21............184.79
7062.5.......0..........22............188.19
7156.25.....0..........22............184.79
7281.25.....0..........22............181.38
7375..........0..........22............181.38
7468.75.....3..........22............177.98
7312.5.......9..........23............160.97
7437.5.......19........31............100.25
7375..........0..........28............-8.15
6843.75.....0..........28............-8.21

As I take my first bounce off the limiter, the knock starts .....and only gets worse for a few samples when I lift off the throttle.

My question is this ....is there a reason why there is so much timing in the low load portion of the high rpm's??? Is there some need or advantage to giving a free-running motor a crap pile of timing??

This picture is two runs, including the one above. The white and light blue dots represent when the knock is occuring.



This is my stock map, not the one I am actually using. The relevant portions of my actual map are the same though.

Could it be helpful to drop the timing way down in the area that I bordered in white??

I can't really imagine a scenario where I would be at 7k, low load in any situation than coming off throttle after a pull.

/thanks malibujack for the load calc app!

 

Well, in reality the knock is due to the rev limiter, or letting off the throttle, Its going to be somewhat unavoidable because its a product of cutting fuel (and ignition in some circumstances) However I wouldn't be too concerned about knock in those circumstances because their not due to combustion..

 

I've been wondering about this as well, after seeing huge knocks at the rev limiter. MJ, can you elaborate on your answer? I mean, if it's 'not due to combustion', but rather the cutting of fuel (or even ignition), does that mean it's harmless?

How do you make that determination? Is it harmless because w/out the fuel, there is no significant energy left in the chamber to cause any actual damage?

I used to bang off the rev limiter all the time when autocrossing my old 300ZXTT, and I occasionally hit it in the EVO as well. I always thought it was harmless, but I never really had a sound reason or factual explanation for that belief.

 

If your not over 15 psi, load, or high cyl pressure I would ignore it. Log a two step to really get paranoid

 

Its basically nothing to be concerned about if the engine isn't under load.. The rev limiter and launch control are rough on the engine, and in turn ot responds by showing as knock.. In reality its not completely harmless, but its the lesser of evils...

As long as you don't get knock under boost, with high levels of load, small amounts of knock are otherwise unavoidable in daily driving.. The same goes for Deceleration, rev limiter, shifting, and launch control, where you will get in some cases very large knock sums...

 

I don't like lift knock though, and I can get rid of it by retarding the 100-180 load range from 3000 upwards so I do. ECU ignores it though.

 

I messed around with this some today just for the hell of it. I brought the timing way down in the high rpm/low load cells ....and it made no difference.

I guess i should have just listened to the advice given and not wasted my time

I did some more logging of coming off throttle ...but not at the rev limit ...and found that I do not have much knock in those circumstances anyway.
I did a 1-2-3 gear pull, shifting before the rev limiter ....and only got a few counts at max torque in 1st gear. Otherwise completely clean. I guess if I want to be paraniod I just need to keep it off the limiter when possible.

 

Pulling some from the lower load zones sorted my lift-off det...

 

Yeah I typically make adjustments to that unless it degrades my daily driving.. In this case it shouldn't because it would be in areas that you may not typically hit.

 

Mine is like that also. I did a 3rd gear 3000rpm all the way to 4th gear redline..0knock..decel 0 knock also..then about 5 min later did just a 4th gear from 3000 to redline and had a few 1's and 2's.. this is all in the same driving time and car never turned off or parameters changed. It is like with the stock ecu you can never completly rid yourself of knock. Also after that last 4th gear pull when I let off my knock shot to 9 counts at 45 load so it was as I was in decel. So I am going to tune my airfuel as close as possible and leave my timing alone for right now until I get my cams that I just ordered and go to the dyno to tune.