Octane Question

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Permalink Reply by canuck451 on April 22, 2008 at 8:51am

I was thinking about it last night and realized this:

The guy selling the car at the dealer is just that... a sales guy. He's not a mechanic or a wrench head or an engineer... he's a sales guy. He's good at what he does: sell cars. (S)He probably doesn't know how fuel octane is measured or even what it means.

That said, even if they DID know about octane ratings in Europe and North America... which conversation do you think they'd rather have:
1) "You have to fill it with 91 octane... see... right here it says that... moving on..."; or,
2) "See here where it says fill with 91 octane... fuel is measured differently in Europe and octane is blah blah blah" (gets out pencil to write down equation, etc).

The first one is MUCH easier and quicker. I wouldn't be surprised if they were told not to get into the second conversation because it might make it seem that they're trying to pull a fast one on Mr. New Car Owner.

That said, it's unfortunate because hitting people in the wallet just after they sign on the dotted line to buy the car by saying "you have to fill it with the most expensive gas there is" is not really a selling point.

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Permalink Reply by mr bad example on April 29, 2008 at 7:25pm

i just took a leap of faith and topped off with 87 PON (the pump had the sticker with MON+RON/2) i'm not a leadfoot and my car rarely gets over 3000 rpms.

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Permalink Reply by Smart Enuf on April 30, 2008 at 4:03pm

Your general explanation of PON, RON, and MON is correct. However, Smart doesn't recommend 91 RON for the 451, they recommend 91 PON. On page 170 of the 451 manual I was given in California, it says:

"Only use premium unleaded gasoline with a minimum Posted Octane Rating of 91 (average of 96 RON/86 MON)."

This comports with the label on the fuel filler flap, which says to use "RON 95 (min. 91)". The "91 min." reference, while a bit ambiguous, seems to be a reference to 91 PON, since 91 PON would result from (96 RON+86 MON)/2. Interpreting this to mean the recommended octane is 91 PON (premium gasoline) is the only way I can see to harmonize what the filler door says with the 451 owner's manual.

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Permalink Reply by mr bad example on April 30, 2008 at 9:08pm

i don't know if it was psychosymatic, but driving home, it seemed i had to press down farther on the go pedal. i didn't hear any weird noises. i had about 6.5 gallons of 87 octane and probably 2.5 gallons of 93 octane, so i figure my mix is about 89 POM in my tank now, i'll top it off in 3 days with the 93 before my trip to road america. weather is supposed to be crappy saturday morning, cold air is good for the engine, (supposed to be cool and humid!) (i fill it up pretty close to the top, ignoring the clicks off)

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Permalink Reply by Jim Mottin on May 12, 2008 at 11:15am

I don't have my manual yet, so can others follow up on this aspect of the octane discussion please.
Thanks,
Jim

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Permalink Reply by canuck451 on May 12, 2008 at 11:29am

Smart enuf is definitely correct and I am half correct. Confusingly enough the gas tank cap definitely indicates 'RON 95 (min 91)' but the manual also definitely indicates a min of PON 91 as enuf indicated.

All I can say is that I have filled 2 tanks with PON 91 and 4 tanks with PON 89 and have noticed no difference - no backfiring, pinging, lack of horsepower or fuel economy.

In this thread: http://www.451s.com/forum/topic/show?id=1912846%3ATopic%3A23194
Smart indicates that you can run regular fuel with 'no damage to the car' but running premium will give you ~2mpg better fuel economy. That last part doesn't make sense to me because your fuel economy can't get BETTER... it can only get worse if you run a lower octane than recommended causing your engine to knock, which the knock sensor will detect and cause your air/fuel mixture to change such that you're burning less efficiently.

To sum up, I don't believe there is a definitive answer... just lots of speculation. To my mind there's no difference between 89 & 91... so I'm gonna switch back to 89 on my next tank.

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Permalink Reply by Smart Enuf on May 12, 2008 at 2:44pm

I think we're both right, and Smart needs to hire a new technical writer. As you suggested, the filler door label's "RON 95 (min. 91)" could easily be interpreted as a minimum RON of 91 and a recommended RON of 95, which would translate to a minimum PON of 86 ((91+81)/2). This would mean filling up with regular unleaded (at PON 87) would comply with the filler door label. It could also be interpreted as min. PON of 91, as I suggested, which would mean filling up with supreme unleaded is required.

All Smart has done with the conflicting door label and manual instructions is to give us smart owners some ammunition to fire back with if Smart tries to claim an engine problem is due to our use of below-spec gasoline. I'm hoping it does not come to that, but hey, it's their messed up manual and filler instructions!

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Permalink Reply by Matthew A Ziminski on April 22, 2008 at 9:41am

It's been a while since my AAS degree in Internal Combustion Engine Technology, But I agree with canuck451. I am intrested in how ethanol mix will change the performance too.

All in all, I will be getting 2-2 1/2 times better gas milage so a dollar here or there, I won't worry about.

beep-beep

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Permalink Reply by Daniel Coté on April 22, 2008 at 10:06am

Matthew,

What's your secret? I'm presently getting 42-43 MPG. I want to know how to get 2-2 1/2 times that (84-105 MPG)

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Permalink Reply by mr bad example on April 29, 2008 at 7:23pm

i think he's referring his smart over his older vehicle.

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Permalink Reply by davel on February 22, 2009 at 9:46pm

FWIW, the 2009 manual recommends 91 PON.
From page 247: "Minimum Posted Octane 91 (Avg. of 96 RON/86 MON)"

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Permalink Reply by smarttask on February 23, 2009 at 8:37am

Shell V-Power 100 ottani petrol in the Smart Turbo 84cv and Shell V-Power Diesel in the BMW


• 100 RON petrol is Shell's new premium fuel
• Shell claims fuel improves power and performance

Shell claims that V-Power provides your car with more power and responsiveness, and it does it in three ways. A higher octane rating of 100 RON means that the fuel burns more effectively, while additives in the fuel reduce the loss of energy in the engine by reducing friction in the cylinders.

The fuel also contains cleaning agents designed to remove unwanted deposits from your engine. Shell says V-Power can clear years’ worth of build-up in just a few tankfuls.

100 ottani, 100% Ferrari.

Migliorare l’accelerazione, avere un motore sempre perfetto e ridurre le emissioni di zolfo. Con Shell V-Power 100 ottani è possibile.



Roger

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