Thread: getting some knock starting around 4800 rpm.. any suggestions?

Originally Posted by 97AutoXVette

Hmm, that's interesting.. How does the IC play an effect into the equation outside of normal inlet air temp cooling? I was under the impression that I wouldn't need an intercooler as soon with running E85 since the added fuel can take excess heat out of the air. Appreciate any more info you have on that end.

AFR is pretty conservative and around 7/1 to 8/1 anytime the engine is under load/boost (down to around 7/1 @ WOT).

I think what it boils down too is E-85 quality. It 87 mixed with ethanol. Perhaps other states use higher quality base fuel to mix with ethanol. I'm in Canada and the E-85 in my region wasn't impressive.
It was about equivalent to 100 octane gasoline at best. AV gas alone at 104-108 octane was far superior.

But I was running 2.6 pulley with the worst possible set up for KR. Just so you know Ethanol although very high octane, the threshold for knock resistance in some situations is much lower than Leaded race fuel. Leaded race fuel tolerates leaner mixtures a lot more than Ethanol. Also leaded fuel tolerate higher intake temps than E-85. E98 or pure Ethanol is another story. The little bit of cheap unleaded fuel is what causes the knock.

So you could be too lean at the moment. Way too rich can cause rich knock as well. You need to provide A/F ratio data.

In your case with the 3.5 and your mods you should never see any knock. What's your A/F ratio I don't think you answered this yet ?

Originally Posted by TwinV6GTP

In your case with the 3.5 and your mods you should never see any knock. What's your A/F ratio I don't think you answered this yet ?

A/F values (on my Wideband tuned for pump gas) are 14.7 @ cruise (target 9.85 on E85).

@ 28% throttle, it adds 1 to the A/F values, which yields between 12.5 and 13 on my WB.

after 45% throttle, full PE targets kick in which are set to 8/1. That yields around 10.8 - 11.0 AFR values on my wideband. I originally targeted 7.3 AFR values as base PE, but was seeing my wideband values of 10.0 - 10.3 during WOT, which seems too rich considering that is sub 7 AFRs on E85.

Let me know if all that made sense!