Originally Posted By: OVERKILL
Further to what stchman is digging at, anybody who has ever played around with cars that had a distributor and could manually change their ignition timing knows that at some point you stop getting gains and will actually start losing power. Every engine has an ignition advance "sweet spot".
So, further to that, an example, the 5.0L Ford (stock, the old pushrod one) shipped with 10 degrees of base timing. This gave the ECM the ability to advance total timing to something like 32 degrees IIRC (forgive me if that's off, it has been a while). It was found, via numerous dyno tests that throttle response and power (to the tune of 5-10HP IIRC) could both be improved with more initial (which subsequently increased total) advance. This engine was 8.8:10 compression IIRC, had your typical wedge shaped chamber and a 4" bore. The "sweet spot" for this engine was 14-15 degrees initial, anything after that didn't increase gains and going much beyond that, as I noted earlier, resulted in a loss of power.
The penalty for this? Well, you had to run 89 or 91 (varied a bit by engine) to ward off detonation. 94 didn't yield any more power and wasn't required to prevent pinging.
With modern computer controls that include a knock sensor and an ECM that varies timing based on the feedback from that sensor, the realization of some additional power MAY be had (greatly depending on the engine, compression ratio, chamber design, bore size....etc) through using higher octane gasoline.
HOWEVER
There will be a limit to how much total timing the ECM will add. It isn't going to just keep adding timing until it pings, the table used for advance has a limit, established by the factory and if 89 for example prevents ping at maximum total advance there is ZERO benefit to running 91 or 93/94.
This is why cars like my wife's '06 Charger for example spec 87 but "recommend" 89. Total advance can only happen with the higher octane fuel. However it will run just fine on 87.
A car with forced induction is another beast all together however, as elevated intake air temps will by themselves create a necessity for reduced ignition advance due to pinging/detonation and depending on how high you drive up ACT's will determine how far down it has to be pushed. Add increased boost and that's a whole other topic altogether and a bit outside the scope of this rambling however
As I've mentioned before, what we were able to glean from our very secretive customer (most good info was obtained via whispers in the corners of dyno rooms or electronics labs) was that they intended to have the knock detection system drive the timing...they really wanted to run at very light knock, far below what the driver could perceive. Whether this really panned out or not, I don't know.
