Dealers and MPG

[lhoboy]

Originally Posted by fishrdnc

To provide an inkling of what the effect of retarded ignition timing can be in order to accommodate lower octane gas, I have my numbers.

In the process of setting up my 1691cc Ford Kent Crossflow engine on a dynamometer we first ran it up on 93-octane, unleaded, ethanoled, road gas, with the necessary timing, to 103 ft-lbs of torque at the flywheel. Subsequent runs on 110-octane, full-lead racing gas, at its proper timing, produced 109 ft-lbs of torque at the same RPM. That is a 5.5% increase in engine output.

Note the Crossflow is not fuel injected and ECU controlled; it is fed by two twin-choke Weber side-draft carburetors (40 DCOEs), and in road trim it was originally intended to run on 97 RON leaded. Only the timing by rotation of the distributor was involved, and the jetting stayed the same.

I used to formulate gasoline in a different life. The additional torque (on the same engine) from the racing fuel actually is a result of two issues. 1) higher octane, allowing a more advanced spark, and 2) blend components providing a balanced distillation curve across the entire distillation range. The latter allows a smooth, timed burn throughout the combustion cycle of the engine. Most commercial grade gasoline is blended to optimize cost rather than performance. As a result cheap components with low distilation ranges are blended with a bit of high octane, high distillation range components, leaving a blend with little in the middle and a very uneven burn.

[MicroNut]

I thought it might be interesting to estimate the smart

[mr_Cash]

fishrdnc,
ihoboy,

if a new smart owner prefers lower priced 87 octane (smart still working on it, but for now, they say 91 octane premium only)

what octane gas do you recommend for a 2008 smart?

thanks.

[SmartBob]

They say lower will work, but for me....no lower than 89 with the info we have now.

[Old smart]

Originally Posted by Mr_Cash

fishrdnc,
ihoboy,

if a new smart owner prefers lower priced 87 octane (smart still working on it, but for now, they say 91 octane premium only)

what octane gas do you recommend for a 2008 smart?

thanks.

Sometime in the past on this forum someone reported that the inside of the gas cap, or the area surrounding the gas fill, was labeled 95 RON, 85 MON. The way the U.S. figures "pump octane number" is PON=(RON + MON)/2, or in this case 90 PON. Also, Euro 95 RON "roughly" corresponds to 91 PON, so perhaps smart took the higher number. It is said to be "4-or-5" numbers different. I would be inclined to burn 89 (just one point below 90) if the 95/85 thing is true for 451s, and if I wasn't putting the car to hard usage. I have the option of mixing our 93 and 89 50-50 to make 91 at a nickel a gallon savings. Fifty cents a tankfull may not be worth the bother though.

I do notice a drop-off in performance and MPG in the H-6 Subaru by burning 91 vice 93.

At high altitudes, Colorado for instance, you can get away with lower octane without pre-detonation (knocking, pinging), but there will be a bit less power too.

[Old smart]

Here’s something. I came across a document that, among other things, compares the results of combined mileage testing between the Euro method (NEDC) and U.S. testing (CAF

[lhoboy]

Originally Posted by fishrdnc

Sometime in the past on this forum someone reported that the inside of the gas cap, or the area surrounding the gas fill, was labeled 95 RON, 85 MON. The way the U.S. figures "pump octane number" is PON=(RON + MON)/2, or in this case 90 PON. Also, Euro 95 RON "roughly" corresponds to 91 PON, so perhaps smart took the higher number. It is said to be "4-or-5" numbers different. .

Typically the difference between RON (Research Octane) and MON (Motor Octane) is 8-10 points. Therefore, the 4-5 point difference between RON and the average PON.

I would be inclined to burn 89 (just one point below 90) if the 95/85 thing is true for 451s, and if I wasn't putting the car to hard usage.

I wouldn't push this issue. The Smart is generating 71 hp/liter. That's equivalent to punching out over 400 horses on a 5.7 liter V8. I suspect the compression ratio on the smart is over 9.5 or 10:1. You never know when you'll need to put your foot into it, and the knock sensing technology that is employed may not be sufficient to retard the spark enough to prevent detonation (permanent damage). Besides, if something does go wrong, that 89 octane gas will void the warranty.

I have the option of mixing our 93 and 89 50-50 to make 91 at a nickel a gallon savings. Fifty cents a tankfull may not be worth the bother though.

$30 vs. $30.50 per tank. As you say, probably not worth the time to reset the pump and reswipe the credit card.

I do notice a drop-off in performance and MPG in the H-6 Subaru by burning 91 vice 93.

I bet you would also notice a difference between 91 and 89 octane on the Smart.

At high altitudes, Colorado for instance, you can get away with lower octane without pre-detonation (knocking, pinging), but there will be a bit less power too.

You can safely run 2 octane points lower on a normally aspirated engine at mile high altitudes. The power will be down, but that is primarily due to the reduced air intake at the higher elevations.

[lhoboy]

Originally Posted by Mr_Cash

fishrdnc,
ihoboy,

if a new smart owner prefers lower priced 87 octane (smart still working on it, but for now, they say 91 octane premium only)

what octane gas do you recommend for a 2008 smart?

thanks.

I would err on the side of caution. Stick with the manufacturer's recommendation (certainly don't buy higher octane). Without adequate engine testing (which the manufacturer is well qualified to do), using lower octane fuel could cause serious engine damage and void the warranty.

[Old smart]

Originally Posted by lhoboy

As you say, probably not worth the time to reset the pump and reswipe the credit card.

I once had the occasion of filling a few pre-hurricane season jerries with 87 for the generator and chainsaw. Then I put half a tank of 89 in the car. When I tried to put another half-tank of 93 in the car (to make 91), American Express took umbrage and shut me off! Had to go inside and pay cash for the 93. Before I got home AMEX had been on the phone with a fraudulent card use alert.

[lhoboy]

Originally Posted by fishrdnc

I once had the occasion of filling a few pre-hurricane season jerries with 87 for the generator and chainsaw. Then I put half a tank of 89 in the car. When I tried to put another half-tank of 93 in the car (to make 91), American Express took umbrage and shut me off! Had to go inside and pay cash for the 93. Before I got home AMEX had been on the phone with a fraudulent card use alert.

I had the same problem on a long distance motorcycle ride. AX will cut off a card if it is used for gas more than 3 or 4 times within the same day. That happened when I rode 850 miles from DC to Florida in 13 hours.