Any Difference in MPG or Performance with Premium (93) or Mid-Range (89) Gas?

[ayap888]

Ok, yesterday was the first time I tried loading mid-range gas. Has anyone observed any difference in MPG and performance with mid-range gas (89 octane) vs. premium gas (93 octane)?

Do tell.

[specialist23]

when we had our 05 fx, i did notice about a 2-3 mpg difference. don't know about the ex yet.

[M45Caliber]

the only difference being octane, only performance at the high end of the spectrum should be affected. The car (all new cars) compensate for octane (or lack thereof) and adjust the timing accordingly. So, under full throttle or travelling up an incline, you would notice a slight decrease in total torque and horsepower, thus, performance.

In day to day driving it should be imperceptable. Your fuel mileage is controlled by a computerized air/fuel ratio and octane really doesn't impact that, so no mileage differential should be measured. However, most Tier 1 premium fuels have more additives and that might be beneficial in the long run for your intake, injectors, valves, piston crowns, etc.

If you are going to measure any difference in fuel mileage, you will need to perform a closed loop test with the exact climatic and driving conditons, using the same driver and technique. Furthermore, the driver can NOT know what fuel is being tested each time, so as not to impact the technique utilized. Way too many variables for us ere mortals to control, but you could use regular for a month, then premium for a month and see -- assuming you drive the same exact routes and speeds both months, which is still all but impossible to do.

You won't hurt the car using 89 octane, but Infiniti recommends premium for a reason. At $0.25/gal more, and figuring 12,000 miles a year at 18 mpg, you will spend about $167 MORE annually (or $14/month) for premium over regular.

You just bought a $40,000 car -- so you decide if it's worth it. Pennywise and pound foolish? Do you extend your oil changes out to 7,000 miles to save money? Why not? Think it through and do what you feel is best for your situation. If you are leasing and don't plan to keep the vehicle past the 36 month (or whatever) term, then regular will suffice and the next owner can deal with any issues that might arise.

[MI3]

Since we are on the topic of mpg, I would like to know if anybody notice mpg drop due to ethanol content. Some of the gas out there has ethanol as much as 10%.

[M45Caliber]

I think general research backs up about a 5% decrease in MPG on "ethanol enhanced" fuel (assuming 10% as you mentioned) I've heard the number for E85 is closer to a 25% reduction in real MPG. See research below:

23% extra fuel cost of using E85 with 2006 modelsThe EPA has measured the gas mileage of 2006 flexible fuel models. For the 31 models they tested the average reduction is 26% fewer miles per gallon. For example a car that gets 30 mpg on regular would typically get 22.2 mpg with E85. This is exactly what is predicted from the fact that E85 has less energy per gallon than gasoline.

For these calculations, the EPA assumes that E85 costs $2.00 and regular $2.20/gallon. Obviously they are on the low side, especially for ethanol, but this proportion is similar to what DOE predict for the next few years. The loss in mileage more than makes up for the cost savings, and on average the EPA predicts driving on E85 will cost 23% more than driving on regular.

[M45Caliber]

From the Web - Octane Myths• High octane gasoline improves mileage.In general, if your car is designed to run on 87 octane gasoline, high octane gasoline will not improve mileage. If switching to high octane gasoline does improve mileage, you might find that your engine, or its control systems, need repair.• High octane gasoline gives quicker starting.No, it doesn’t.• High octane gasoline increases power.If your car is designed to run on 87 octane gasoline, you shouldn’t notice any more power on high octane gasoline. Again, if it does make a noticeable difference, your engine, or the engine’s electronic controlsystems, may need repair. (NOTE: Infiniti recommends Premium)• High octane gasoline has been refined more – it is just a better product.Additional refining steps are used to increase the octane; however, these additional steps do not necessarily make the gasoline a “better” product for all engines. They just yield

[CaribMon71]

I usually fill up with 87 octane. I have compared the total miles I can get from a tank of 87 to a tank of 89 or 91. There is a definite difference in mileage every time between the 87 octane and the higher grades.

I get more miles with the lower grade octane. I believe this may be due to the reduced performance induced by the timing retardation.

Does this sound possible? I had a VW Touareg V8. I noticed the same thing. Same thing with my Lexus 250 IS.

[dividedhighw]

I get more miles with the lower grade octane. I believe this may be due to the reduced performance induced by the timing retardation.

Unless it's due to reduced temptation to squirt past other cars!!

Cheers,David

[CaribMon71]

But I'm not as tempted in Virginia! Actually, I drive like a pansy here. Now if I had this car back in Puerto Rico... OMG, would I have a blast! When I had my Touareg in PR, triple digit speeds were common on a weekly basis.

Even though there are many more police cars checking for speeding back home, they don't have radar detector laws, no photo radar, no laser detection, no speed detection from planes... and even if you get caught, your insurance rates don't go up. Besides, so many people speed, it's hard for them to focus on just one car.

Now back to my theory. I'm wondering if the amount of fuel delivered to the chamber is affected by the timing (advance/retard). When you retard the timing, combustion is occurring on the piston's down travel. But is it still the same amount of fuel that is being delivered?

If it is, then my theory is probably incorrect. If fuel is reduced, then I might have a point. Anyone know?

[scottrod]

Octane. The higher the value, the less likely the fuel is to detonate (knock).

Think of it as a "knock-value." Higher compression ratio engines, and engines that run advanced timing to adjust for cam curves, engine speeds, and the like need the higher octane rating to prevent detonation in the combustion chamber. For aviation fuels (low compression ratios) altitude is also a player.

All M45Caliber says is true. I don't know how the EX35 engine is designed (yet), but I'd bet it has a knock sensor or something similar that retards ignition timing or cam timing if knock is detected, like maybe when you're running on lower octane fuel and stomp on it. I can see how the mileage might be reduced a little with the lower octane fuels as the retarded timing will also decrease the power generated per stroke a bit.

I run the 93 octane stuff, but don't drive the car that much so the annual cost differential isn't too great. I'd say if you're an acceleration freak that likes to put your foot in it (ok, guilty, the wife too) I'd run high octane, as you're less likely to have detonation issues (which are very, very bad) and might even notice a little better performance if you're really tuned into your car on a zen level. OTOH, if it's just your wife puttering around town, I'd go for the lower stuff, certainly the mid-level fuel is fine.

Notice also BTW, the higher gas prices go, the better value the high octane is. When gas was $4 a gallon the high octane was the same 20 cents a gallon more than the lowest octane stuff (around here anyway).

I run BP fuels in my cars for the rebate they give me and Sunoco 94 octane in the Lotus for the detonation prevention as the accelerator is usually on the floor.

Anyone know what the compression ratio is in the EX35? That pretty much tells the tale as to where it's living with regards to detonation, seeing as how it must have reasonable cam profiles and timing for the masses.

[CaribMon71]

I don't understand your statement about airplanes having lower compression engines. I know that high altitudes (on land) normally only require a lower octane rating to prevent knocking and up in the sky temperatures are lower. It would appear that there would be a lower risk of knock. But why then are aircraft fuel octane ratings above 100? That made me think that aircraft engines were high compression engines.

(I searched and found this after my initial post): Aircraft piston engines are typically designed to run on Avgas. Avgas has a higher octane rating compared to automotive gasoline, allowing a higher compression ratio and thus more power out of an engine with the same engine displacement. Currently the most common Avgas is 100LL, which refers to the octane rating (100 octane) and the lead content (LL = Low Lead). Guess I'll be looking to wikipedia for that one.

As far as this statement:

I can see how the mileage might be reduced a little with the lower octane fuels as the retarded timing will also decrease the power generated per stroke a bit.

this is the opposite of what I was asking.

The last I checked (maybe 2 years or more), knock sensors were microphones. Timing was retarded once knock had already occurred. I believe you had to shut the car off and restart it to get the timing back to normal again. This was to prevent if from happening again. Has that changed?
Modified by CaribMon71 at 3:51 PM 4/6/2009

[scottrod]

High-performance aircraft engines like the aerobatic and racing engines have compression ratios in line with higher-performance automotive engines, around 10:1 or even 11:1 if you're really into it and have a death wish for your propeller.

The engine speeds are much lower though, only 2700 rpm or 2800 rpm wide open throttle. This is because what you want in aviation is torque, not horsepower. My 6-cylinder Lycoming engine has 540 cubic inches of dieplacement and makes 260 hp at sea level, but has 506 lb ft of torque. Compare that to the EX35 that has 297 hp at 6500 rpm but only makes 240 ft lb of torque.

The flame front in the huge combustion chamber of an aircraft engine is much slower moving (relatively speaking) than that a high reving auto engine and has a much greater propensity to detonate during flame propogation, hence the need for a higher octane fuel, regardless of compression ratio.

Also, you can't hear detonation in a plane like you can in a car, and it can burn a hole in your piston very quickly and kill you, also unlike a car. More conservative factors are applied to octane rating to help keep people alive (and decrease lawsuits!).

[CaribMon71]

Ok, I think I understand. Thanks for clearing that up! Cool, you have a plane?

[dividedhighw]

Notice also BTW, the higher gas prices go, the better value the high octane is. When gas was $4 a gallon the high octane was the same 20 cents a gallon more than the lowest octane stuff (around here anyway).

Well, I wish I was in the US because you folks pay much less, not only for cars, but also for gas.

In Ontario, 91 octane gas usually sells at $0.12 more per litre. Since a litre is hovering around $0.80, that's a 15% difference!!! (Sunoco 94 octane gas in comparison costs another $0.14 per litre, or 17.5% more.)

So, at only $0.20 more even on a $2 gallon, you're only paying 10% more for 93 octane!! What's with that?!? Do the oil companies think Canadians are just that much more gullible or simply that much worse at math?!!!!

David

[ayap888]

Is it because you pay more taxes in Canada, that gas prices are higher?I know that gas prices are also quite expensive in Europe. But Canada and Europe has free health care and heavily subsidized education, and we do not have that in the US.

So I suppose that's where higher taxes are going.

[BrokenTiller]

Yes. Higher component of tax in our fuel costs. Cost of oil and refining, transportation, marketing, etc. should be essentially the same as in the USA.

If you are curious, current price in Toronto is approximately $0.85 CDN for a litre of regular gas. Converts to ~ $2.59 US per US gallon.
Modified by BrokenTiller at 6:54 PM 4/6/2009

[RioD007]

After my +2 mod i have to ALWAYS burn premium or it will knock... not that i wasn't before haha.

[dividedhighw]

Hey RioD007 ... so, do you now have 20" wheels or 19" wheels?

FYI, PM is not enabled on NICO.

Cheers,David

[RioD007]

Hey RioD007 ... so, do you now have 20" wheels or 19" wheels?

FYI, PM is not enabled on NICO.

Cheers,David

Thanks for the info. Ill change that in my sig.

By + 2 I mean my engine's timing has been bumped up 2 Degrease to give it more power and more aggressive acceleration. It is possible in all of our cars to have this enabled but its difficult finding a dealer thats willing to do it. From what my stopwatch tells me on 100 octane and somewhat balled tired I did a 0-60 run the other day around 5.2 seconds. It truly did make a HUGE difference.



PS if you guy's would like any more info this just ask.

[ayap888]

I went for the mid-grade and it did affect MPG.

1st fill - 21.07 (premium - break in period)

2nd fill - 21.8 (premium)

3rd fill - 23.0 (premium)

4th fill - 20.9 (mid-grade)

5th fill - 22.95 (85% premium with 15% mid-grade) .. 365 miles with 15.9 gallons.

I'm going back to premium only ... mid-grade takes 10% off MPG.
Modified by ayap888 at 3:21 PM 4/13/2009

[cjre1]

the only difference being octane, only performance at the high end of the spectrum should be affected. The car (all new cars) compensate for octane (or lack thereof) and adjust the timing accordingly. So, under full throttle or travelling up an incline, you would notice a slight decrease in total torque and horsepower, thus, performance.

In day to day driving it should be imperceptable. Your fuel mileage is controlled by a computerized air/fuel ratio and octane really doesn't impact that, so no mileage differential should be measured. However, most Tier 1 premium fuels have more additives and that might be beneficial in the long run for your intake, injectors, valves, piston crowns, etc.

If you are going to measure any difference in fuel mileage, you will need to perform a closed loop test with the exact climatic and driving conditons, using the same driver and technique. Furthermore, the driver can NOT know what fuel is being tested each time, so as not to impact the technique utilized. Way too many variables for us ere mortals to control, but you could use regular for a month, then premium for a month and see -- assuming you drive the same exact routes and speeds both months, which is still all but impossible to do.

You won't hurt the car using 89 octane, but Infiniti recommends premium for a reason. At $0.25/gal more, and figuring 12,000 miles a year at 18 mpg, you will spend about $167 MORE annually (or $14/month) for premium over regular.

You just bought a $40,000 car -- so you decide if it's worth it. Pennywise and pound foolish? Do you extend your oil changes out to 7,000 miles to save money? Why not? Think it through and do what you feel is best for your situation. If you are leasing and don't plan to keep the vehicle past the 36 month (or whatever) term, then regular will suffice and the next owner can deal with any issues that might arise.

+1. Well put. BTW: 91 Octane will give you about 1-2MPG more. Proven study, plus a cleaner burning engine, quiter engine, etc. $40K car, you need to spend for the best. You did when you bought the car.