Originally Posted By: DBMaster
Some on here claim that using premium fuel allows the engine to re-tune itself. I haven't bought into that.
I bet an engine like that would absolutely benefit from a higher grade of fuel. I've found that with most modern engines. Our MDX calls for premium and we use it, and feel and see (via Torque app on my phone) timing advance differences when using regular gas. Our Ridgeline calls for regular gas, and we use premium in it. Same deal as the MDX -- you can absolutely feel the difference in power and response with premium, and that's supported by timing advance numbers you can see in black and white on Torque. Hills that are JUST steep and long enough to cause the transmission to unlock the torque converter in high gear with regular fuel can be crossed without unlocking the torque converter with premium fuel. And that's with a relatively old design 10.5:1 V-6 engine. It's obvious that both of our V-6 engines have the range in spark advance to be able to take advantage of the greater octane, despite Honda rating one for premium and one for regular for obvious marketing reasons.
I bet a thoroughly modern 12+:1 4-cylinder could absolutely use the extra octane from premium fuel. Said another way: it's probably not advancing the timing on regular as much as it would if you were running premium. "Re-tuning" is an instantaneous process, and is really simpler, I believe, than some make it out to be. In short, the computer is always looking to advance the timing as far as it can without inducing damaging spark knock. Regular fuel just causes it to not advance it as far as it could on premium.
I'm sure there is a practical limit to the range of advance. But I bet the range it uses on regular fuel isn't it.