This guy has it right and rather than type all this I just did a copy paste but I agree with what this guy posted he has it right and he explains some of the myths about fuel.
Within practical reason premium fuel and regular fuel burn at the same rate. Premium fuel resists detonation better than regular so the explanation that it burns slower or faster was invented to explain this in-explicable phenomenon. That is called an old wives tale. The burn rate is the same. Period.
This gets murky, however.
As long as we are talking pure gasoline then premium and regular burn at the same rate.
There are very special blends of gasoline that do have different burn rates....like the magic stuff of formula 1 legend. We are talking pump gas here, right?
There are other ways of improving the octane rating of the fuel than just making better gasoline. Adding lead, as mentioned, will increase the octane rating and will not affect the burn rate. Adding alcohol (either methanol or ethanol) or some other oxygenates will also improve the octane rating of fuel. Alcohol burns slower than gasoline so gasoline spiked with alcohol will burn slower than straight gasoline. I believe this is the reason for some of the confusion and explains some of the "testimonials" from experts that claim "their motor made more HP on regular fuel than premium" and that "regular has more energy than premium." Likely they tested with some premium gasoline spiked with alcohol and they didn't change the jetting and spark timing accordingly.
As a matter of fact I have seen many engines on very accurate dynos run on both premium and regular fuel (these were engines designed for regular) and the power was exactly the same and the optimum spark timing was exactly the same. If the fuel burned slower or the burn rate changed then the optimum spark would change accordingly. Proof that the burn rate stays the same.
Normally aspirated engines at altitude are running somewhat throttled due to the lower atmospheric pressure. The cylinder pressure of an engine at WOT at altitude will be like the same engine at 2/3 throttle at sea level. That is why octane requirements at altitude are reduced and premium fuel at altitude will always be about 3 or 4 points lower than fuel at sea level.
Don't confuse octane rating (the fuels resistance to detonation) with volatility (the vapor pressure of the fuel). Volatile fuel will boil or generate vapor at lower temperatures and/or volatile fuel will create more vapor at a temperature than a lower volatile fuel would. Volatility affects the fuel's ability to vaporize or atomize in the intake tract and combustion chamber. Winter fuel is much more volatile than summer fuel. High altitude fuel is much less volatile (within the same season) than low altitude fuel. Volatility can also affect HP significantly depending on the engine and fuel system as the better the fuel atomizes the more completely it can burn and the more oxygen in the air is used. Many times power differences blamed on premium/regular are really due to differences in volatility without the tester realizing it. Aviation fuel is very low volatility even though it has high octane rating. I have heard lots of people claim av gas "won't make power" without realizing why....it's the volatility, dummy.
Some racing fuel can have very low volatility, also. Low volatility helps resist vapor lock ..... vapor forming in the suction side of the fuel line as the fuel pump tries to pull the fuel from the tank. I know of one specific case where a racer ran some race gas and pump gas and found more power with the pump gas and presented the results as proof that the lower octane fuel had "less energy in it". Wrong. The race gas was too dead to atomize completely and hurt the air/fuel distribution to the point that the power dropped. The pump gas was more volatile, atomized well and distributed well and made more power.
Old wives tales die hard....but there is usually an explanation out there to explain how they got started.
BTW....it is detonation or pre-ignition. "Pre-detonation" is not a word and not a condition.
Detonation is the spontaneous combustion of the end gas in the chamber. Detonation happens after the spark ignites the charge in a normal fashion. Causes a very very rapid pressure spike in the chamber that "rings" the structure of the chamber much like hitting it with a hammer. That is what you hear. It is NOT the sound of the flame fronts colliding. Another old wives tale.
Pre-ignition is a situation where the charge is ignited BEFORE the spark plug ignites the mixture. You will never hear pre-ignition. You'll hear the piston breaking up and parts chewing each other but not the pre-ignition that caused it. Pre-ignition is always deadly because the piston is coming up while the charge is burning and creating huge pressure trying to stop it. Piston looses.
Detonation often occurs near the exhaust valve because the exhaust valve is hot and heats up the mixture making it prone to spontaneously combust and cause detonation. Not because it ignited the tail end of the mixture. If that happened it would have lit it off much sooner and been pre-ignition.
