To the OP, your statements seem pretty accurate. 18* timing is probably riding the ragged edge, which is unnecessary. Optimum timing in mild n/a motors comes well before detonation. So, you will reach peak power, and still have several more degrees of advance before you reach detonation. Let's say you actually peak at around 14*. You're not likely to see any difference at 15, 16, or even 17* advance. At 18*, you're flirting with detonation, and before you hear the motor ping, you're likely to start losing power. So, you'll see it on a dyno before you pick it up by listening. Adding any more advance is only going to make the detonation worse, and your power output will suffer as a result.
You're right, most people here don't have stock compression. The OP does though. So why does he need more octane than I use in my 10.5:1 setup?
Because he wants to run more timing, and make the most power he can. Plus, 10.5:1 is only one part of your motor's story. What are the cam specs, and how much timing are you running on 87 octane?
[qoute]The point is, you shouldn't be upping timing to the point where you are upping octane to.[/quote] That's an opinion. Others are willing to pay a bit extra for the extra power or the added insurance against detonation.
not true
In fact, you're probably losing power by doing so.
Explanation, please?
If you're running 18 initial timing with 93 octane, you're probably running at least 38 degrees total. What for?
For the fact that some cars want 18* initial timing. My old car ran a best ET and trap speed at exactly 18* initial. Of course, it had AFR165s, and a custom cam. I had that car on multiple dynos and was at the point of tuning fractions of a degree of timing, and 18* on the nose it what worked best.
I'm not saying that this timing is right for the OP's car. In fact, I'd tend to believe his pointer was off before I believed his motor liked 18*. However, the likeliest possibility is that he's advanced his timing beyond MBT, and is running at the ragged edge with no gain in performance. Backing it off is probably right, but dropping octance probably isn't, if he's going to shoot for peak power.
Didn't you know, just4bob50 too, that 87 octane has more energy in it than 93 does?
Theoretically this is true. However, the difference in thermal energy is negligible, and the difference in power from more advanced timing is not. In other words, the thermal efficiency gained in the combustion process by advancing timing with higher octane fuel outweighs the loss in its chemical potential energy.
In pretty much any N/A application, the experts will tell you somewhere between 32-36 degrees total timing will give you the most power, depending on exactly what your setup is like. So if you're running 38+, you're really losing power.
Are you sure that the A9L strategy advances base timing by 20*? Second, we cannot establish with certainty that he is really running 18*. The pointer may be inaccurate. Third, my pointer was not inaccurate when I got my best performance from 18*. So, the expert apparently has a flawed opinion. Something tells me that there's more to the story.
I have tried this time and time again at the track, 91 octane and more timing doesn't get me down the track any faster (sometimes slower) than when I use 87.
How much power were you expecting? Is your driving consistent enough to see a 5-10hp difference? Were you keeping track of your coolant/engine temps, and the tracks are temps? If every other variable is held constant, you should see only a delta of .05-.1 in ET and .5-1mph in trap speed.
Chris