Just a preface, with my daily commute on regular 91 octane I get around 260-280 miles out of full tank till the empty light comes on. 17 mpg roughly.

Last weekend I went golfing to Sonoma as usual. On the way back I was running out of fule so I stopped at the racing track and treated my car to some 96 octane. $3.52/gallon, I got $32 worth. After fillup my gas gauge was reading two notches above half. Engine revved smoothly and sounded good. For the next 4 days. And belive me, I was revving it more than usuall. Today at 230 miles light comes again. According to my calculations this is 25.5mpg, and that's mostly city driving with lead foot in hilly San Francisco on short distances with not much time for proper warmup.

I'm shocked. I also want to know where do I go as a consumer to urge manufacturers to sell higher octane at any pump, because even at $3.52/gallon it makes a lot of sense, not to mention that I waste less fuel and car feels more responsive.

***04 G35s 5AT/Sport***
***04 Volvo XC90 T6***

I'd be amazed too if I suddenly got 7-8 mpg better mileage with a change in fuel. But I don't find your method of calculating this particular mileage very compelling. You're relying on a guess of how much fuel was in the car at the time you added the 9.1 gallons of race fuel and a second guess of how much fuel remains in the car when the fuel light comes on. That makes your calculation of 25.5 mpg a guess too.

I've never found my mileage to vary much from the 17.5 mpg I get in daily driving. I haven't taken many road trips but that's where I would expect to see the improvement.

Octane is added to fuel to prevent pre-ignition and detonation. Especially important in high performance/high compression engines. It adds nothing to the power component of the fuel. A high octane fuel has a slower burn than a lower octane fuel. If you don't experience pre-ignition and detonation (knocking) with 91 octane fuel, you're only decreasing the engine's performance by adding high octane (slow burn) fuel. Your gas mileage should go down not up as you have less power available from the fuel for similar driving.

Anyway, gas companies have very successfully marketing high octane fuel as high "power" fuel when it is really low power fuel. It's just that high performance engines need low power fuel to run properly. When you exceed the point where you solved the problem of detonation (91 octane for our G35s) adding additional octane is actually counterproductive.

By the way, my car feels faster after I've washed it. I think this might be some of the effect you've noticed from the 96 octane fuel.

Cale

04 G35X

Ethanolized or MTBE oxygenates mixed with gasoline decrease the BTU per gallon so it takes 3-5% more gasoline to go a mile. Racing fuels use higher aromatics to meet octane they don't require oxygenates to add octane, so in theory you might get 3-5% better mpg [maybe].

Premium gasoline only sell at 13% of total [87% reg and midgrade combined] Nationally.......and that is with only a 20 cent differential............

I know what you mean about car being faster after a wash
It didn't seem faster per se, but engine kissing redline felt very smooth.

The only logical explanation that I can think of is that gas from the track doesn't have any of the "engine cleaning" additives we get here in Cali. I will be going golfing every weekend and will definately continue experimenting with that.

I though that when light comes on solid ( no on-off crap) we have close to 3 gallons left in the tank. Again I refiled today with regular gas managed to squeeze in 16.8 gallons. So that number is pretty consistent. Fact is the fact from one light to another with 9.1 gallons added - 230miles.

This is the second time I'm getting flamed for using high octane on the internet. If my mileage is consistent with existing observations, I will just start silently doing this every time I have a chance and be quiet about.




***04 G35s 5AT/Sport***
***04 Volvo XC90 T6***

OMG q45tech once in while said that it is not BS



***04 G35s 5AT/Sport***
***04 Volvo XC90 T6***

He said 3-5%. 3-5% of 17 is 0.8 mpg. even 13% is 2.1 mpg



Better Life thru Chemistry
Black on Black 03.5 Sedan 6MT - Goodyear F1 GS-D3's 225/55/17, Custom Intake Tube, '03 "Z" Suspension, Magnaflow resonator, 6 Wire 4 Guage Grounding Kit

MOTOP:

I've got your back on this one, MOTOP. You are not imagining this.

I have several times in several cars experienced what you speak of, i.e., using a higher octane grade fuel giving me better MPG vs. a lower octane fuel. Whether or not it makes up the difference between the extra cost of the fuel vs. the extra mileage is a case by case basis, but the car usually runs better and I (therefore) have a smile on my face that's worth something. Depending on the car and/or engine, it sometimes makes no difference at all.

For example, in my '91 Pontiac Bonneville SSE (3.8 liter naturally aspirated V-6 w/4AT), I got 2-3 MPG better with premium 91 octane vs. mid-grade, and I experimented with this several times, in both around town driving and long highway runs, both. Same story with my wife's '96 Accord EX w/SOHC VTEC 4 Cylinder & 5MT, and my son's '98 Acura Integra.

No discernable difference in the '86 Mazda Pickup (carbuerated 4 Cyl w/5MT), and in fact, I believe it ran better and stronger with regular unleaded while getting the same mileage, so Cale Johnson may have something there, too.

I live in the east bay area, and hope to make a trip to the Sonoma area soon, and visit the Infineon Raceway to fill up on that racing fuel and try it out myself.

Keep reporting your results, I, and a large silent majority, would like to know how it plays out, and your observations. I'm sure you'll keep more precise records in the future (by completely filling the car up, then zeroing the trip odometer, then filling it completely the next time and precisely calculating miles driven and fuel consumed). This will help quell the flamers, but will more importantly settle the matter for you, yourself (which is what's most important).
My $0.02 .......

Sport Sedan Fan - 2004 6MT Sedan
Sport/Navigation/Premium/Aero; "Invisiguard" Bra, Madico Onyx Tint
Obsidian Black/Graphite & "Titanium"
SHE'S SILVER & BLACK - GO RAIDERS!

Geez. Thanks for explaining how percentages work. Maybe next time I can have a trigonometry lesson.

Usually Q45tech is very sceptic about stuff like that, but this time he said MAYBE, which I hear very rarely from him here and on Nico. So that means it is not unusual to see mileage gains from higher ocatne, even though not as drastic as the ones I had.




***04 G35s 5AT/Sport***
***04 Volvo XC90 T6***

Dbarnes, we posted at the same time. Thank you for support. My previous reply wasn't addressed to you.

***04 G35s 5AT/Sport***
***04 Volvo XC90 T6***

Sorry, but I simply refuse to believe you found a 50% increase in fuel economy by changing the gas. (17mpg x 1.5 = 25.5mpg) I'm not saying you aren't telling the truth. I'm just saying I don't believe it. I was surprised by your claims and wanted to know if you might have made a mistake in calculating the data. It's been said that I sometimes lack tact, my apology.

04 G35X

MOTOP, one real effect you might notice with higher octane fuel is determined by the range of the ECU's timing maps. I suppose it's possible that your perceived smoothness may be due to a lack of detonation, and the ECU running with the most advanced curve (of its multiple curves). Although I'm frequently at Infineon, it's always with my truck (kart in the back). I've never been tempted to pay nearly double for fuel - it wouldn't help on the truck anyway. I did notice better mileage on a trip to Oregon after running on "real" fuel (no MTBE). This was with a Mopar perfomance ECU mod., which is designed to accomodate racing fuel octane. However, the difference was only about 2 mpg. (not really statistically significant given one sample). It would certainly be useful in understanding the ECU algorithm better to have some additional data, with accurate mileage computations. As stated, added octane lowers the energy density of fuel. However, it does allow for more timing advance without detonation, which increases engine power output (up to a point!). When the ECU senses detonation, it will retard timing. It's possible that there is an optimal fuel octane which balances these two opposing effects, timing retard (and lower efficiency) - too little octane vs. poor fuel energy density - too much octane. Maybe that point, for our engines/ECU is somewhat higher than 91?!? Anyway, I would expect changes in your driving style to much outweigh fuel differences. Maybe you drive differently after a long day golfing??? A couple of mpg improvement seems feasible, but your results seem too good to be true. Well, keep us posted anyway. Now if we only had a timing advance ****...

2004.5 G35 Sedan | Garnet Fire + Willow | 6MT | Z-Tube, K&N panel | Stillen Cat-Back

MPG is pretty simple.
The factory dyno the engines and measures the volumetric efficiency vs rpm and throttle opening. Within a narrow range the engine can only absorb so much air for the atmospheric pressure, the MAF tells the ecu how to adjust for temperature , pressure, and humidity.

So the ecu KNOWS within 3% [or better] exactly how much air is in the cylinder. For emissions purposes the O2 feeds back a correction signal to adjust fuel to 14.7 {+- 0.2]................now oxygenates FOOL the O2 sensors into believing that the exhaust is too lean, so ecu trims the normal mixture to make the O2 HAPPY...............this tiny extra fuel use with oxygenates is where the decrease mpg comes from.

Indeed MPG is that simple assuming a theoretical cycle. It appears that it's substantially more complex in the "real world". I found Chevron's site to be very informative:

http://www.chevron.com/prodserv/fuel...enrgycon.shtml

For example:
The potential work that a fuel can do is determined by its energy content. One measure of energy content is British thermal units (Btu) per gallon. Oxygenated gasolines contain less energy per gallon than conventional gasoline:

The values in the table for the reduced energy content of oxygenated gasolines represent only the volumetric effect of replacing higher-energy-content conventional gasoline with lower-energy-content oxygenate. Often, particularly for gasolines oxygenated with MTBE, there is an additional energy content reduction related to changes in the gasoline portion of the blend. Since adding oxygenate increases octane, refiners adjust the octane of the gasoline portion so that the octane of the finished oxygenated gasoline will be the same as the octane of the conventional gasoline it replaces. The adjustment involves substituting lower-octane gasoline components for higher-octane components. Since some of the higher octane components, particularly aromatics, have higher energy contents, the adjustment lowers the energy content of the gasoline. The additional decrease in energy content is about 0.5 percent.

So, since oxygenated gasolines contain 3.5 percent less energy, they would be expected to yield a proportional reduction in fuel economy.


2004.5 G35 Sedan | Garnet Fire + Willow | 6MT | Z-Tube, K&N panel | Stillen Cat-Back

I'm going to revive this thread.
I hope everyone had nice and eventfull Labor Day weekend.

I went to Sonoma on Saturday and took a plunge at my favorite gas station. 16.2 gallons at 3.58/gallon. Also enjoyed watching Shelby track event. Since that I have put 200 miles, 110 of them is city driving. Needle is exactly at half tank right now. I know this is not as drastic as my first observation but it is still a gain. I also should add that at no point of this weekend I had less than 2 people in the car and the air conditioner was on the whole time, not something I usually do. 104 on Sunday.

Another thing I've noticed driving on 91 octane over the week and than filling up with 96. Remember somebody reffering to our engines feeling like "truck engines", difference is exactly the same. On 96 octane engine just pulls easily and wants to keep revving. On 91 it seems like it is fighting to get to the redline.


I will post another time when this tank is gone.

Please don't flame, I'm not trying to prove anything. Just spending my money the way I like and share observations.





***04 G35s 5AT/Sport***
***04 Volvo XC90 T6***

Okay...

1. Did you fill up?
2. Let's look at total miles vs. the # of gallons on your next fill.

This should give us a more reasonable MPG figure. I'm looking forward to those numbers...


<font color=red>chinee</font color=red>
03.5 G35s