I'm at my wit's end trying to get rid of my engine knocking since moving to Colorado where you can't get higher than 91 octane. For the first 40K miles on this bike in TX, it always got 93 octane and while there were occasional knocks in the hot summers, it wasn't really an issue. Since being in CO on 91, it will knock every single ride, no matter what temperature outside, once engine temp gets above about 220F, MODERATE throttle use either accelerating from a stop or on the highway to pass, I hear light knocks and my PV registers knock events. Obviously it gets significantly worse as engine temp increases.

I've tried everything to adjust my tune to get rid of it. I first tried running PV logging runs and pulling timing in trouble areas, in some places up to 6 goddamn degrees. Didn't make a difference. So I said **** it, I'll just go back to stock spark tables and let adaptive knock control do its thing. Doesn't work, still knocking at moderate load. It doesn't seem like adaptive knock retard is doing anything to mitigate the knocking and there's no way I can see how much spark it's pulling. So I've resorted to pulling back timing in basically the entire spark table one degree at a time and now at 2 degrees across the board(except idle) I feel a decrease in performance but NO decrease in knock events. And this is still with adaptive knock control on. What the hell?

And when I say it does it at moderate load I'm talking 50-70 Kpa MAP. It actually DOESNT knock as much near WOT.
I'm running a closed loop tune with adaptive control on. My fuel map runs on the richer side, with closed loop cruise areas at 14.3(0.976 lambda). On average closed loop integrator trims 5-8% back at this altitude, so in other words, I'm not running lean anywhere on the map.
I've scoped the cylinders, noting a normal but not excessive amount of carbon on the piston tops. I use combustion chamber cleaners on a semi-regular basis.
Plugs are NGK DCPR8E and always look very light brown and dry. No notable metal specks showing signs of detonation.
Bike burns no oil.
At 45K miles and mods are listed in my sig.

Are these engines not designed to run on 91? I just don't get it. Should I just ignore this knocking and not worry about it? In my experience, knocking at mid-load isn't nearly as serious as at wide open, but I still worry that years of even light knocking will cause excessive wear.

 

When i had my 14 sgs out there i got a lot of pinging, i took it to the Harley dealer in loveland, they had me use octane booster which helped alot but didn't eliminate totally.

They also told me that they have taken engines apart with 50k or more that spent their entire time up in the mountains and seen no issues with the pinging.

 

Yeah the thing is that octane boosters only add a tiny amount of octane and they're not good for O2 sensors long term.

But that's good to hear at least. Thanks.

 

while it is true that ping is the sound of most efficiency, still not a good thing.
When cylinder pressure peaks before TDC, bad stuff happens. Why? It could be one or more of the following things: too low a fuel octane, an insufficient cooling system, a poorly designed combustion chamber, too hot a spark plug, too much static compression, too little overlap between the cam's intake and exhaust lobe, too lean an air/fuel ratio, too much preheating of the intake charge, or in the best case, an improper ignition curve.
i will throw this slinky out and see if it walks.
i had a dodge 440 with the same issues and nothing worked and still had good results but the blame was on me, sooooooo
i installed a holley water injection system and nary a peep. it was vacuum controlled and temperature controlled.

 

Have you tried OEM spark plugs?

 

Yes, of course. And funny thing is when I went to Mile High Harley to get new plugs recently, they only had the NGKs available.

 

I would try copying the spark tables and paste them over to the left one column and see what happens. Because at altitude you’re cruising at a lower kpa now than before. If the VE tables are TPS based then I would also want to collect data and get those corrected for the altitude. Yes it’s not going to have as much power as it does in Texas because the pressure is lower.

 

Welcome to the fuel we get west of the Mississippi river. Be glad you can at least get 91 as even that's not everywhere in the west, you can typically count on finding 89 octane but in some areas all you can get is 87. Your going to need to retune your fuel side first then work on your timing tables.

 

I understand your thinking, and obviously I understand density altitude's effect on performance. But 50kpa is 50kpa whether it's at sea level or mile high. Detonation risk is based on timing at a certain kpa(for a given temperature), so if for example I'm at 40 degrees advance @ 2500rpm and 50kpa, the variables that matter are the same regardless of the local altitude. You may be right about the TPS based VE tables needing adjustment, but as I stated my tables are biased towards the rich end, with closed loop always pulling back fuel. So there's no way I'm running too lean. I did move my lambda table values over to the left to compensate for the fact that at this altitude my max kpa is now 85 instead of 100 at sea level. That was to ensure that the AFR at WOT is appropriately enrichened. Again, I'm not really knocking much at WOT, it's at mid throttle settings.

 

Remember one cubic foot of air is not the same amount of air at both sea level and 6000'. The more important thing is the amount of Oxygen in the air and it is reduced the higher you go. It's more a stack of small changes that occur as you travel higher that add up to get you into trouble along with the lower octane fuel. Now if your VE tables and everything else in your calibration were MAP based it would be much closer but that's not how HD has done it. Go back and get the fuel corrected first than work on the timing.