While looking through the provided XGauge codes on the SGII for my car, I came across the "knock retard" value and plugged it in, just for kicks and giggles. From what I understand, this gauge is supposed to report the degrees of ignition retard from the current timing due to detected detonation by the knock sensor. I didn't think this would provide much valuable information, as it initially just read 0 most of the time.
I later noticed, however, that when accelerating in the higher gears this gauge started reporting knock retard at above 24 in. Hg manifold pressure at 2400 RPM, and above 22 in. Hg after the torque converter lockup clutch engaged at 1500 RPM. I began using this gauge as a reference when accelerating, maintaining the highest possible manifold pressure without causing spark knock.
I had no idea that there was any spark knock going on in the engine, I have never heard it before. Apparently, this is the peak cylinder pressure that the 87 octane/E10 can handle in my engine with the default timing values. I guess I can run all the way up to 29.9 in Hg at 100% load, but it seems that this comes at the expense of retarding ignition timing, which I'm guessing is a cause of the loss of efficiency that I have seen with heavy engine loading in the past. Not to mention that there is detonation occurring that is damaging to the engine. This number would usually go up to about 10 or 20 under moderate acceleration, but I watched it go up to around 60 when passing. So this means that on 87 octane/E10 I can only expect a useful load of 74% from my engine.
I will experiment with some higher octane fuel when prices come down a little, or next time I am near the gas station that sells midgrade for the same price as regular
. This is an interesting find, it will definitely influence how I drive from now on. I am wondering if anybody else has had any experience with this value and might be able to enlighten me as to whether or not this is what is actually occurring.