EU vs US octane rating & the benefit of higher octane

GTamas · Apr 26, 2024

In Europe we use a different octane rating than what is used in the US.
The standard fuel here is 95 octane, which AFAIK equals 91 octane in US system. It is an E10 blend.
What octane fuel were the 94-95 5.0s designed to run on? If lower than 91 and I use 91 fuel, what can I do to use the benefit of higher octane? Advance the ignition a little? Any drawbacks? Is it worth it?

shovel · Apr 27, 2024

If you have the stock heads then your compression ratio is 9:1 and you could run Euro 90 (US 87) at sea level without a worry in the world. If you aren't running forced induction or increasing your compression ratio there isn't much you can do to deliberately take advantage of a higher octane fuel. You will have more freedom to adjust timing with a more stable fuel but the performance value of doing that with a compression ratio of 9 and above sea level is negligible. If you tuned rich and advanced the base timing a degree or three you might see some WOT power but you'd also be depositing a lot of soot on your oxygen sensors, cats and EGR valve which doesn't strike me as a long term strategy worth hunting.

If you greatly increased aspiration (performance heads, cam, intake manifold) then you'd be filling the cylinders with more air and even with the same compression ratio you'd want to run a little more advance. Flames travel faster in denser air so you start the fire earlier. A higher octane fuel would allow that to happen just right in a wider range of temperatures and throttle positions without knock.

ju015dd · Apr 27, 2024

GTamas said:
In Europe we use a different octane rating than what is used in the US.
The standard fuel here is 95 octane, which AFAIK equals 91 octane in US system. It is an E10 blend.
What octane fuel were the 94-95 5.0s designed to run on? If lower than 91 and I use 91 fuel, what can I do to use the benefit of higher octane? Advance the ignition a little? Any drawbacks? Is it worth it?

Does your car still have the cats and egr?