I've always ran 91 octane in my 05 Sportster, which is a carbureted bike. It doesn't take much gas and doesn't get much miles since I live in Canada and we only get like 6 months riding time and Harley says so.

In my cars however, I run regular. I've tested premium in them but doesn't seem to make any difference. Regular in Canada is 1.16/litre (thats 4.39/US gallon).

Watch this...

 

premium gas is not worth it if your owner's manual says your car doesn't need it.

 

I run what Harley Recommends- premium. We don't pay quite as much for gas as you guys do. Right now I'm paying about $0.50 per gallon more than our E10 87 Octane, but for that extra money, it's E0, which is becoming easier to find around here. So it costs me about $2.50- $3.00 additional per fill. I don't know how well (or poorly) the bike would run on the 87 octane stuff, manual recommends premium so I figure they know better than I do.

In the car and truck I run 87 octane E10- what the manual recommends. We can't get 87 octane E0 around here, and technically we're only supposed to use the E0 stuff in motorcycle, boats, lawn mowers, classic cars, etc..... Not sure how if that is ever enforced though.

 

Pretty much any non-tuned engine can run regular. Makers anticipate various fuel quality levels coming from who know which station in who knows which city.

Comes down to compression (not really the ratio but the pressure). I always use Premium but it's not likely needed in most of my vehicles. Anything tuned - definitely, unless the tuner deliberately tuned you for standard gas - I know I need high octane in some of mine.

In Canada, you standards may be better (or better monitored). I would run premium in any high performance engine.

 

Its all about engine compression and octane, high compression engines require higher octane than lower compression engines.

 

So where's the cut off? Most Harleys are at about 9:1 - 9.5:1 compression. I can't see that requiring 91 octane. I built a few motors for a 66 Chevy II 1/4 mile car I had. It had high compression pistons and heads about 14:1. We ran Av gas in that. Why should 9:1 HD's require 91 octane or more? Some family cars are as low as 7:1.

 

I haven't ran premium gas in any vehicle I've had in the past 10-12 years. And I've never had any problems at all. When I want them to move, they do. The only one in the past 20 years, was one that had a turbo powered engine and I used premium with it.

 

It's not just the static compression ratio. Cylinder pressure is what matters. Timing, CAM duration, air temp, other factors all affect pressure. You need to know your pressure.

 

Reaper's engine is built to 10.5:1 compression. If I run low octane gas, she pings like crazy. So for me, yes, it's worth it. I always get the highest octane available.

Cheers!

 

Depends on the vehicle...
Most of the vehicle I have owned (except the diesels) we run regular unleaded.
But some (very few) actually do better with higher grade fuel.
We had a Honda civic SI that actually got better fuel mileage (if driven the same) with supper unleaded.
My bikes, the EVO, 01 & 09 twin cam's did fine with regular unleaded, But my 17 103 does not like the lower grade fuel.
So I started running the higher grade/octane, but only from a place with separate hoses.
I am not sure what the pump & hose hold, but I have been told it's more than you might think.
I keep my tanks on the top half, so that is about 2-2.5 gals at each fill up on the bike.