Can being too rich cause detonation?

[Fred 86 GN]

My GN is running well, but it keeps getting some knock retard and a knock count at WOT. It never goes above 3 degrees of KR, and most of the time is less than 2 degrees. I would like to tune for zero knock.

Here is an example of when the knock retard occurs:

boost pressure = 17psi
4000rpm
820mv from oxygen sensor
27ms of injector pulsewidth
LV8 = 255
MAF = 225
fuel pressure static with vacuum removed = 42psi
running a mix of octane in the tank -- 10gal 93 and 5gal 110
chip base timing at WOT = 23.6 degrees

The KR is not occurring at a shift. It really does not seem to be triggered by anything shown on DirectScan. The DirectScan A/F ratio is less than 10:1 when the knock retard occurs.

Engine has a RJC power plate installed, 009 injectors, TE-44, CASV4, 3-angle valve job and relief above the valves in the stock heads. The power plate has reduced the KR some. :smile:

I don't think the engine can use 90-95% of the fuel capacity of the 009 injectors at 17psi. That would be over 450hp, and based on a 107-109mph trap speed I believe the engine is more like around 380hp in the present tune.

So if it is rich, can that cause KR?

Thanks,

 

[azgn]

seems rich.....turn the boost up or fuel pressure down & see what happens.....cannot live & die by an 02 reading, but the only way to tell is to experiment (or get some more tuning devices. like an egt, WB 02)

 

[REDS HOT AIR]

my car has no knock problems at all and it runs best (by butt dyno) with the 02's in the 820 range...thats were i run mine all the time.

 

[TurboDave]

Just because you're running rich, isn't going to stop detonation. There's a point when you're going to go beyond the fuel's octane ability to supress knock (that, after all, is what octane is all about).

17# of boost in 3rd gear is pushing the limit on ordinary premium fuels, especially now days.

Lot's of folks seem to forget the basic premise of octane ratings and what they're for, and concentrate too heavilly on the amount of fuel being delivered. Doesn't matter how rich you run, once you get past the fuel's ability to suppress knock (octane), usually with too much boost for the octane being used, it's going to start detonating.

 

[Fred 86 GN]

Thanks for the replys

Guess the next experiment is to run the gas level down a little bit more and add another 5 gallons of 110 octane then see if the KR is reduced.

If no change, then figure it is either a rich detonation condition or something mechanical is banging. Then I can try turning the boost up or the fuel pressure down and see if the KR goes away.

If no change, then something mechanical is causing the knock sensor to ring and I can ignore it. The shroud on my CAS V4 intercooler does buzz when I rev the engine...maybe it could be to blame.

 

[gnXfan]

What chip are you running? Are you spinning the tires when the knock occurs?