Premium Fuel

why is there a need for premium fuel? It seems that this will negate most of the fuel savings

Permalink Reply by Ian Pellant on December 14, 2008 at 10:04pm: US Octane ratings are different to most of the world that uses the RON standard. Add a few points to US octane to get RON equivalent.

US premium unleaded equates to 95 RON. I've been using 98 RON more than the recommended minimum of 95 RON, due to availability. The current service station trend here seems to be to drop the 95 in favour of 98. There does not appear to be any performance difference in the pulse turbo between 95 and 98. Australia does not get any fuel lower than 91 RON... except maybe some of the ethanol mixes.

It seems that using a higher octane fuel than recommended generally does not give a performance increase... but using a lower octane fuel than recommended will generally downgrade performance.; ▶ Reply to This

Permalink Reply by DAN on December 15, 2008 at 2:45am: Dear Ian,

I got it. My 05 Smart does says to add 95 RON fuel to it. All this time by using Premium 93 I was following the instructions. As to my 08 Smart always premium. I have noticed that some stations sell gas with 10% ethanol and some have 15% ethanol. Never the less smart is very censitive to quality of the gas. Sometimes as and always I go the gas stations with higher prices simply to make sure that I get what I paid for. But on weekend it is a disaster. I could not wait for 245 miles to pass to end the tank with gas that does not feel to be 93 eve when I paid for premium.

Thanks again,

Dan; ▶ Reply to This

Permalink Reply by Ian Pellant on December 16, 2008 at 2:57am: Hi Dan,

I've had the same experience over the years... run low on fuel and pull into the nearest service station and have to buy some dubious fuel, or nothing... A tankful of bad fuel is a curse. With my smart, when new and just delivered the fuel was a bit dubious, but it didn't need to be top stuff because one should not rev and stress a new engine. However, consumption was way higher than expected and I ran down to the flashing low fuel gauage very unexpectedly, in the boonies. There was only one petrol station... looked like a reject from a redneck '60s movie. Dubious... I put just enough of their "premium unleaded" in the tank to get back to civilisation.

I haven't used standard (91 RON) unleaded in the pulse and won't unless really desparate. I unwittingly filled with an ethanol mix with my Subaru, a few years ago; it has a 95 RON recommendation. The ethanol blend was notably down on performance and economy. I have no desire to use ehtanol blends in my smart.; ▶ Reply to This

Permalink Reply by Daniel Coté on December 14, 2008 at 9:59pm: "93oct and the car runs faster."

You're kidding, right?; ▶ Reply to This

Permalink Reply by mr bad example on December 15, 2008 at 5:00pm: i've been running my smart on 93 most of the time and once in a while i run 87, i don't notice much difference, but i'm not hot-rodding my smart. i got a scan gauge now, so i can monitor the ignition advance (right now i monitor RPM, GPH, MPG and coolant temp, i did have it on ignition advance and it was all over the place for a short run) 93 and higher octanes are for high power, high reving, hot running engines that might pre-ignite with more "flammable" lower octanes.; ▶ Reply to This

Permalink Reply by Ian Pellant on December 16, 2008 at 2:57am: The ignition advance reading on the SGII will shift all over the range, similar to the LOD gauge. The only way I can get any sort of meaningful reading is on dead flat cruise trying for a steady state, or more telling is I have a hill nearby with an 80 kph speed limit up a km of road (a sod to cycle up!) and a set of traffic lights at the bottom that love to turn red. Early morning, no traffic, stop at those lights, then accelerate briskly to and hold 80 kph and monitor LOD and IGN on the 'Gauge. I saw more retard (less advance) on the Subaru when using RON 91 than RON 95. I haven't done these tests on the smart (haven't used RON 91 fuel).

In theory, the smart ECU will retard the ignition and avoid knock (pre-ignition) with lower octane fuels... Other factors: you're under snow now? Winter mix fuels have something added to assist cold starts?

PS: got the SGII fine tuned, It predicted 16.6 litres to fill. At the pump today: second click off at almost 16.7 litres... most accurate setting to date.... mark that as a pump to use next time!; ▶ Reply to This