[Brian894X4]

The higher or lower energy with the different fuels will come up a lot in this type of discussion. It's important to point out this has nothing to do with more or less energy in the fuel. Its entirely about the fuel anti-knock qualities and whether one fuel's anti-knock qualities will allow the engine to run at peak performance when it no longer has to compensate for the lower anti-knock fuel.

9 to 1 compression is not low and there's a misconception that it is. All things considered, 9 to 1 would normally need as high as 96 octane to prevent knocking, but computer management and fuel injection of the 1FZ and other engines that rate that high are able to compensate. However, if you could ever run 96, you wouldn't need to utilize the computer management system to retard timing and compensate for the lower octane and it would run at peak performance. There's a lot more to it than just compression of course, but that's where the theory is headed. Most engines, especially older EFI engines and just about any other engine with basic ignition advance systems, won't allow the computer to take advantage of the of the lesser knocking fuel, because engineers don't want to risk the engine going beyond safe parameters while still using a higher knocking, lower octane fuel.

Everyone seems to get stuck on the idea that there's no reason to design a motor that runs better on 92+ and especially 96+ when it's not available. It's not that engineers went out of their way to design the motor to run on gas almost no one will ever see. It's that the engines, via their higher compression these days and other factors, naturally will run better on the higher octane if the engine management system will allow it. But many don't for the reasons I just mentioned. It's not worth the risk in case the timing advances too far on low octane fuel and the knock sensors aren't working properly.

If you wanted to design an engine specificly to run only on 87 octane or even lower octane, the first thing you'd do is reduce the compression to as low as 7 to 1 or maybe 8 to 1 maximum. You're mechanically making the engine 87 octane friendly, and thus needing no or little management to compenstate. But when you mechanically limit the engine's performance, you limit it across the board. On a new engine with more advanced managment, its better to crank up the mechanical design and use the computer management to limit the engine's perfermance depending on which fuel it happens to be using.

That’s my theory here, based on what I’m reading and I think a lot of newer Toyota and a few other engines also take advantage of lesser knocking fuel, when available, because the engineers had more confidence in their anti-knocking system design.

So, a reasonable question would be then, why would engineers make any engine with higher compression than 7 to 1, if they are going to limit the management system as if only 87 octane was available. That's a good question and the answer may be that even with the engine compensating for knock, a compensated 9 to 1 compression engine will still out perform a non-compensated 7 to 1 compression on the same type of fuel, all else being equal.

Again, my theory, still researching......