Filed under: MPG
Can using premium gas increase your efficiency? If so, is it worth it?
creative commons - NatalieMaynor
The issue of premium vs regular gas has always been a controversial one. Oil companies have long claimed that their premium blends provide more power or efficiency than regular fuel. The problem is that real world results tend to be be very mixed. While it's true that using a higher octane fuel can allow an engine to generate more power and/or run more efficiently, the engines have to be calibrated to take advantage of these fuel properties. Many modern engines with sophisticated electronics are capable of doing this, but not all.
According to AutoCar one machine that does benefit is the Vauxhall Astra VXR. While Saturn dealers only get the normally aspirated 1.8L Astra, the VXR version gets a turbocharged 2.0L engine. In testing with premium and regular gasoline, the engine produced 17 hp on premium while also getting a mileage bump from 22 to 25 mpg (18.3 to 20.8 mpg (US)). Turbocharged engines like this definitely have an advantage because they can run higher boost levels compared to normally aspirated engines which have fewer parameters to adjust. The question is, does a 13 percent bump in efficiency outweigh the extra cost of the fuel and the extra energy to refine it? That question remains unanswered.
[Source: AutoCar]
Reader Comments (Page 1 of 1)
Mike Z 8:15PM (12/14/2008)
"The question is, does a 13 percent bump in efficiency outweigh the extra cost of the fuel and the extra energy to refine it? That question remains unanswered."
Regular: $1.65
Premium: $1.85
Difference: 12%
Your question is no longer unanswered.
Of course, we gas was $4, the difference was more like 7%.
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Mark 8:35PM (12/14/2008)
*very* tough question. I believe you must split the discussion into turbo and non-turbo vehicles.
I have a 1995 VW VR6 non-turbo that supposedly requires premium fuel. I did a test for a while where I did 3 tanks 87 octane and 3 tanks 91 octane... back and forth for a while. I couldn't make heads or tails of the results. MPG varies so wildly for many other reasons. I do have a pretty regular drive schedule of 30 minutes on the freeway twice per day on my long commute.
However,, my car now has 215k miles on it and during the hot months this summer it was tending to knock under load so I swtiched to high octane for the summer and back to 87 for the winter.
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Mike Z 10:03PM (12/14/2008)
Incidentally, I am the only one who loves it when I'm driving though the middle of nowhere are get to fill up from one of those old analog pump?
It just seems to a step back a simpler time.
I remember seeing a gas pump in a junk yard that could not go over 99 cents a gallon and had a sign saying the price was '2X' I guess the first time gas went over a dollar.
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Dr. Kenneth Noisewater 10:08AM (12/15/2008)
Yup, I recall filling the bike up at an olde style pump in eastern Oregon, very hilly, dusty terrain, glad I actually had cash!
Incidentally, for some reason which I can't fathom, in my state mid-grade gas is like 30-50 cents more per gallon, and premium is an additional 20-40 cents.. WTF?
Benoit Cerrina 10:52AM (12/15/2008)
a post like this in an automobile blog is kind of weird I think.
There is nothing misterious at all to this. You should follow the recommendation from your manufacturer and you will be fine.
And contrarely to what is said in the article it is not when your engine is "modern with sophisticated electronics" that you can best take advantage of it. An older engine which requires premium can be damaged by pinging if you use regular (specially the kind available in the US) while a more modern engine will just loose efficiency AND power at the same time but will not be damaged.
I could see this very clearly recently when after Huricane Ike there was no more premium or silver at the pump, both our cars which normally should take respectively premium and silver (an MX5 and a 3.5 magnum) had to go with regular, both felt noticeably more slugish and drank noticeably more fuel
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Phil L. 11:28AM (12/15/2008)
Older engines couldn't automatically detect the level of octane in the fuel, and adjust the engine to take advantage of it.
Modern engine control systems with knock sensors can advance ignition timing to *just* the edge before detonation occurs. If it senses the beginning of pinging, it will retard timing - which is why your cars didn't like post-Ike gasoline. So yes, it has much to do with electronic engine controllers.
Of course, old time hot-rodders knew how to advance their distributor. But they had to do it by hand, and couldn't account for other variables that affect detonation. Which explains many of the trashed motors I heard about when I was a kid...
kide- 10:57AM (12/15/2008)
I didn't find any difference between regular 95 octane and Shell V-Power (~99,7 octane).
I'm driving 2007 Seat Ibiza FR. (1,8 Turbo)
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charlie w 11:27AM (12/15/2008)
Yeah I thought that the standard recommendation was common knowledge for auto enthusiasts....
premium gas cars built in at least the last 10 years will not be damaged by using lower octane, but you'll probably get less power and efficiency. Cars designed for regular will get no benefit from using premium.
with regards to the Autocar test: I don't know about the Astra VXR, but turbocharged cars usually specify premium fuel. If Vauxhall specifies premium (91 to 93 octane) fuel for the car and then they ran it with regular (87 octane) versus 99 octane, then this is a very misleading article. The electronic engine control would retard the engine to decrease heat and prevent knocks... obviously decreasing output and mileage, but using 91 octane fuel would have gotten you the full performance, you wouldn't have needed 99 octane.
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Gabe 11:33AM (12/15/2008)
The octane rating just tells you how the gas can handle compression.
Gas will combust from either compression or spark. If it combusts from compression (pressure), than it fires off of the timing and you get engine knock and possible damage. So you need enough octane (or equivalent on the rating system) in your gas to keep your engine from combusting the gas. Each engine has a different compression ratio, so each engine has different octane needs.
If you have a high preformance, high compression engine, than you should use a higher octane. Follow the manufacture's instructions.
Some/most modern, high compression engines (that normally use premium) can downtune (lower the compression) themselves to use regular gas, but because the engine is running is using less air, it can't make the same power than it can on premium.
Getting miles out of a gallon on has nothing to do with the gas itself, in terms of energy content.
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Luke 12:05PM (12/15/2008)
I've tried various grades of gasoline in my vehicles, and it makes no measurable differences in the mileage.
Furthermore, the owner's manual for my 2.5L I4 Ford Ranger says something to the effect of: "Under no circumstances does burning high octane gasoline provide any benefit, even if you live above 7000'". Having experimented with these parameters while checking my mileage and listening for knocks, I have no choice but to agree with the team of highly experienced engineers who designed my engine. :-)
Gabe @ 9 has hit the issue right on the head. If you want to get some benefit from high-octane gasoline, you need to change your crankshaft and your ECU. Most of us don't have the stomach for that -- I'm a reasonably-useful backyard mechanic and an engineer-of-sorts, and I'm not about to make those kinds of changes to any engine I rely on.
If you want better efficiency without a lot of number-crunching, get a lighter vehicle with a smaller frontal-cross-section. Or failing that, get a hybrid with an advanced aerodynamic shape -- like the Prius.
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CNCMike 12:08PM (12/15/2008)
With my current car,2004 Mazda 6 Sport Wagon, and my previous car, 1998 Plymouth Breeze, I always got better mileage on 87 octane. Both cars will top 30 mpg but only on 87.
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Robert 1:08PM (12/15/2008)
We don't get the Astra VXR in the US and we don't really need it having the Mazdaspeed3, GTI, and even the new Cobalt SS. However, that wonderful 2.0T engine does come in the Solstice GXP, Cobalt SS, and HHR SS. It's one of the few cases, the only case I can think of, where the hi-powered engine gets significantly better mileage then the base one.
Can you think of any other examples of this? I know the defunct Honda Accord hyrbird was a bit of a hot rod and I guess the Lexus LS 600h fits the bill too. There's talk of the 2.0T being a Camaro engine if gas towards $5/gal again as it eventually will. Audi has done well selling the 1.8/2.0T in their seemingly oversize products. BMW would be very wise to put a 2.0T in the 1-series and pass it off as the new 2002 Turbo.
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kballs 2:35PM (12/15/2008)
Same old story. If your engine was designed for 87, you won't get any benefit from running premium gas. If your engine was designed for premium gas, you WON'T save any money by running 87 as MPG goes down proportionally, and you WILL lose performance.
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bradkaye 7:26PM (12/16/2008)
Actually, running 89 in a car designed to run 87 can improve mileage, at least in the case of my 2000 Isuzu Rodeo. I had been running 87 for quite a while in it and was aware around town how it would perform under different conditions, one of which was a considerable I-75 South hill climb about 4 miles north of downtown Atlanta.
At 75 mph, about 2/3rds up the hill, my truck would always kick out of overdrive to make it up the hill. When I upped to 89 octane, the low rpm performance improved and because the engine wasn't about to knock under load in top gear it would stay in overdrive for the entire hill climb.
I gained about 1 mpg on the freeway on that V6 engine by running 89, and overall drivability improved because it didn't hunt lower gears as often.
Ironically, my fire-breathing 445hp (Diablo-tuned) 2006 SRT8 Magnum gets better mileage on the highway at any speed than that 205hp SUV did, of course, I have to run premium in it though.
side note:
Before this latest gas outage this fall, 93 octane premium was always only 20 cents / gallon more expensive than 87 octane. 10 cents/gallon for 4 octane points from 89 Mid-Grade was a no-brainer in a performance car, but when fuel rose over $4/gallon, there was a 30 cent price difference between the 3 grades.
Now, fuel is under $2 for 87 in Atlanta, yet premium is still 30 cents more expensive. I don't imagine this discrepancy will ever revert again.
Paul 3:32PM (12/15/2008)
I did my own tests on my '06 Lexus GS300. It was, as others have attested, a mixed bag. I actually got BETTER fuel economy, but I chalk this up to vastly reduced power and a feeling of "OMG, I'm going to kill it" if I ever tried to punch it a little. The car felt anemic. And it just screamed THANK YOU when I put premium back in. So for me, I decided it wasn't worth it. I might actually have saved a little, but why on earth would I want to pay extra for a (semi) performance vehicle and then lose all semblance of the fun that I paid for just to save a couple bucks a fill-up?
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