And in your case, learn what may happen to the timing advance in your engine when the recommended octane isn't used.

Long before you will hear a knock, your Delphi engine management has already retarded the timing to prevent detonation.

 

I agree completely. I have three bikes that I ride consistently (two main ones) - my wife has 2, but really only rides 1. On my 3 bikes, I average around 9,000 to 11,000 miles a year. They are my babies. I pamper them. In my truck, I use regular. In my car, I use regular. In my bikes, I use premium, if available. If not available, I use the mid grade. They may not need premium, but premium won't hurt them at all.

 

all the petrol volkswagens i have had has run 1-2km longer per liter off fuel with 98 compared to 95, that was messured on the tank not trip computer.

since we are regulated up are asses here in denmark only shell has 98, so i now only use 95 ill have the bike dyno with 95 so i know it runs 100% for that fuel.
and yes on can say that the ecu can regulate for the lower octan fuel, is the bike/car optimised for 98 it will lower the performence alot more the if it´s is tuned to 95.
ps. here in denmark there are shell refinery in jutland and statoil on sjaelland the cheap companies get fuel from the bottom that means there is alot more crap in that fuel compared to the one´s that pay alittle more that is a fact.
over here the meters are checked regulary so you get what you pay for(you may get a little more on the cold evenings and mornings)

regards
RIX

 

Rix, the fuels we get in Europe are rated by a different octane rating to the one used in North America. Daft but true! The octane numbers are similar, but not the same and a US 91 octane isn't the same as a EU 91 octane.

 

Im going to chime and in and be the Devils advocate here. Seems most would agree that premium is best. I have a 2005 Sportster R.. (supposed to have a bigger cam) Ive always ran regular gas in it. Right now I have a tank of 91 octane in it (premium) and it runs like CRAP! Im playing with the choke at stop lights, there's a hesitation at low end - crap! It even RAN ON after shutting it off which is has NEVER done before!

2) In the "old days" I built and raced 1/4 mile cars. The best engine I built was a 350 that was bored and stoked into a 383. It had small cc heads (I can't remember the capacity of the heads but they were 2:02" valves. This car was making huge compression, somewhere north of 14:1 and we ran AV gas in it.

Later in life, I was studying to be a commercial helicopter pilot. We had to learn about gas. The AV gas was BLUE so we students couldn't F*** it up by putting the wrong gas in the wrong helicopter. As it turns out, AV is nothing more than kerosene. So if the 14:1 1/4 mile race car would run on something as heavy as kerosene, why won't a 9:1 Harley run on regular gas?

3) there was a recently a TV show on this topic. They tested cars on the emissions after running regular gas vs "better gas" and guess what? NO DIFFERENCE.

3b) they DYNO tested the same car, with "regular gas" vs expensive gas and guess what? NO DIFFERENCE!

No PERFORMANCE difference, NO EMISSIONS difference!

SO why does Harley "recommend" 91 octane? I think it comes down to this; THERE LEGAL DEPT!

If you read their manuals, EVERYTHING says after it "NOTE: THIS COULD CAUSE INJURY OR DEATH"

Its basically a way of covering their asses, saying "we told you so". Something wrong with the motor? oh? can you "PROVE" that you have ONLY run 91 octane in this bike since new?" of course not. NEXT!...

It's a crock of sh** folks! Like the gas companies are not already making enough money? It's just marketing off your fears! Here's the show...

 

Get your **** straight......AV gas is not kerosene, Jet A is. It's a refined form of kerosene, and is not considered AV gas.
Put it in a piston operated machine and the engine will seize up.
Take from someone who has seen more then once the aircraft wreckage from someone putting Jet A in a piston popper.
Jet A (kerosene based) is only for turbine engines. Today's Jet A isn't even suitable to run in today's diesel engines.
https://en.wikipedia.org/wiki/Avgas

I do agree with you, 91 octane is not required in most Sportster motors.

 

That "corn crap" was used for long time before lead was discovered to be a cheaper "octane booster". Some guys got rich quick on leaded gasoline and they fought against ethanol comeback with everything they had. Your statement is actually theirs. There is nothing wrong with ethanol or methanol, they both have much higher octane rating than gasoline. This is why they are used in racing engines. There are some drawbacks, like ethanol blend is not very stable, you do not want to store it for a long time. But it is absolutely OK to pour into your tank and go for a ride.

 

You're right. there were two types of machines we used for training the Bell 206 which was a jet helicopter and the R22's and 44's (piston machines)

When doing the DI's (daily inspections) we had to make sure the right gas was in the right machine and sign for it.

With the race car, back in the day, they used to let us drive right on onto the airport to fill up.

Point is regular gas is fine for a 9:1 compression engine.

 

I run 91. It's not a big difference financially.

 

It is claimed up to .8 gallon is the gas pumped previously.

It depends how hard you are on throttle. Go wide open and the low octane fuel will detonate instead of combustion.