Smart Car of America Forum banner

1 - 20 of 41 Posts

·
Registered
Joined
·
786 Posts
No problem, mileage does not suffer. The issue with the hi-octane is simple. As with all hi performance engines (can you belive that hi performace engine in a smart car) the compression is high.

If you have a low compression engine, you can use lower octane gas with no problem, but, take that same engine and mill the heads, put in a long travel crank, a high dome piston etc and it increases the compression.

When the compression is higher, you need to run a higher octane gas so that it EXPLODES with the spark from the plug, not to early due to getting compressed and then heated (like a diesel).

Bottom line is, with lower octane gas in this engine, you may, and that is a may due to computerized controls experience lower performance and/or "spark knock". You will NOT have lower mileage.
 

·
Banned
Joined
·
4,883 Posts
I don't know much about engines but I know that if I fill up my smart with regular gas my mileage drops about 4-5 mpg... I've only done it twice and both times it happened.... Seriously though.. you're talking about what 20 cents a gallon at the most??? Just put the premium in it...
 

·
Registered
Joined
·
197 Posts
When I use regular I always get a 20% drop in milage(low 40's to low 30's) and engine knock. Since premium is less than 10% higher, its cheaper to use premium.
 

·
Registered
Joined
·
499 Posts
US model Mitsubishi's with 10:1 compression ratios (like US smarts) specify mid grade (89) octane gas. My local Mitsubishi service manager told me running premium is a waste of money unless you have 10.5:1 compression or higher OR a turbo engine. I've been running mid-grade for the last few weeks and am getting between 41-45mpg which is what I got on premium.
 

·
Registered
Joined
·
334 Posts
This topic has been completely beat to death in other threads and there is no consensus as many have very strong opinions here. For the extra cost for an entire tank of gas (between 1.60 and 2.40 depending on the differential between the two grades) I'm going to put in premium like the book says to. Its less than a cup of coffee at Starbucks and you still spend less in gas than most other vehicles running regular.
 

·
Registered
Joined
·
66 Posts
Ditto...

Running premium fuel as opposed to regular grade raises the cost of day-to-day ownership a whopping.... 1/2 cent per mile - that's it! Am I willing to pay 1/2 cent per mile for:
A) Better acceleration
B) Smoother idle
C) Less 'stressed' engine management
D) A liitle better mileage (yes, it's true)
E) Overall general peace of mind

Darned right I am! Besides, you get the added benefit of always watching the OTHER people's faces as you fill your tank with premium for about half of what they pay to fill their's with regular. To coin a phrase... Priceless!

Cheers,
Jeff
 

·
Registered
Joined
·
22 Posts
Premium Performs Better for Me

I did a 2000 mile test on my 2008 Passion Coupe, 4 tanks running 92 octane and 4 tanks running 87 octane. I got significantly better mileage with premium (41.0 mpg) than with regular grade gasoline (36.8 mpg). The mileage was enough better with premium that, even with the higher cost of premium, I got a slightly lower cost per mile with premium ($0.10) than with regular grade gasoline ($0.11).

MrJack
 

·
Registered
Joined
·
11,471 Posts
I did a 2000 mile test on my 2008 Passion Coupe, 4 tanks running 92 octane and 4 tanks running 87 octane. I got significantly better mileage with premium (41.0 mpg) than with regular grade gasoline (36.8 mpg). The mileage was enough better with premium that, even with the higher cost of premium, I got a slightly lower cost per mile with premium ($0.10) than with regular grade gasoline ($0.11).

MrJack

And once again, common sense rules ! :D


:smartje.rd.zw:
 

·
Registered
Joined
·
81 Posts
This is the way I explain it to my guest when they ask that question.

Look at it from the numbers standpoint, the car is configured to look for 91 octane or better.

If you run regular 85 octane, the vehicle is going to try and get to that magic 91 number. It is going to dump more fuel trying to get to 91.

What this means to you is loss in mpg, you can get a rotten egg smell, this is from unburned fuel getting into the cat, and you can get engine ping.
 

·
Premium Member
Joined
·
10,363 Posts
Since it is a eight gallon gas tank, it would not cost too much more to fill up with premium. I changed to premium and the cost difference is not much at all; especially with premium now less - at most places in NJ - to less that $3 per gallon. :)
 

·
Registered
Joined
·
833 Posts
I did dump some regular in my smart today. It was $1.99 a gallon. Put $10 in to top off the tank. I just couldn't pass up $1.99 gas. I usually put premium in and there was 3 gal. of it left. I never thought I would see $1.99 gas again.
 

·
Registered
Joined
·
9,026 Posts
Listed below are the four basic qualities of fuels. As in everything, there are trade-offs. You can't make a fuel that has the best of everything, but you can produce one that will give your engine the most power. The key to getting the best gasoline is not necessarily buying the fuel with the highest octane, but getting one that is best suited for your engine.

1. OCTANE: This does nothing more than rate a fuel's ability to resist detonation and/or preignition. Octane is rated in Research Octane Numbers, (RON); Motor Octane Numbers, (MON); and Pump Octane Numbers (R+M/2). Pump Octane Numbers are what you see on the yellow decal at gas stations, representing the average of the fuel's MON and RON. VP uses MON because this test method more accurately simulates racing conditions. The conditions under which fuels are tested using the RON method are not as demanding, thus the number is normally higher than the MON rating. This leads many other fuel companies to rate their fuels using the RON in an effort to make them appear more resistant to detonation. Don't be fooled by high RON numbers or an average -- MONs are the most relevant ratings for a racing application. Be aware, however, the ability of fuel to resist detonation is a function of more than just octane.

2. BURNING SPEED: This is the speed at which fuel releases its energy. At high RPMs, there is very little time (real time - not crank rotation) for fuel to release its energy. Peak cylinder pressure should occur around 20° ATDC. If the fuel is still burning after this, it is not contributing to peak cylinder pressure (which is what the rear wheels see).

3. ENERGY VALUE: An expression of the potential energy in the fuel. The energy value is measured in BTUs per pound, not per gallon. The difference is important. The air:fuel ratio is expressed in weight, not volume. Generally speaking, VP's fuels measure high BTUs per pound and thus, have a higher energy value. This higher energy value will have a positive impact on horsepower at any compression ratio or engine speed.

4. COOLING EFFECT: The cooling effect on fuel is related to the heat of vaporization. The higher a fuel's heat of vaporization, the better its ability to cool the intake mixture. A better cooling effect can generate some horsepower gains in 4-stroke engines, and even bigger gains in 2-stroke engines.

jetfuel
 

·
Registered
Joined
·
163 Posts
I have run on 87 oct regular , only because I was on a trip in a region where premium was not available at all for a couple weeks. The Smart ran fine as would be expected BUT there was a noticeable decrease in power output at a given rev range which was easily noted when going up grades. Also I would drop several miles per gallon. I didn't have any problems with starting issues or anything like that.

I would NOT run regular fuel including ethanol again without a good reason as in premium fuel was not available. The Cabrio runs OK on it, but it don't like it.

YMMV
 

·
smart happens here!
Joined
·
1,830 Posts
Two added "benefits" of premium.....

This happened to me months back during the initial gas price spike above the $3.00 gas range. Word got out of the impending increase, and the lines at our local SAM's were long. But evidentally what made them longer was that the regular pumps were running slow - like 10 min/fill!! I pulled in with my 8 gal smart, selected premium and was filled in a minute or two! (Boy did I get some evil looks from the SUV owners!)

And of course the second "benefit" goes along with the first - less likely for a station to run out of premium!?
 
1 - 20 of 41 Posts
Top