djmano

ive been starting to notice recently that the performance of my 8 is greatly affected by the type of gasoline put into it. i had been using arco 89/91 for a cuz it was really cheap, but decided to switch back to mobil. with mobil 89 my car ran wayyyyy better than with the arco 91. maybe its just the arco by my house, but the gas there is really horrible and saving 10-15 cents a gallon isnt worth it. with the mobil 91, the car runs really good excellent throttle response but burns gas like a ****. on average i experience 5 mpg less with the mobil 91. my friend who has been a shell fanactic forever told me to fill up there. i filled up with shell 89 and my car ran the best it ever has. i really feel that a high quality gas stations 89 octane is the perfect gas for the 8. 91 octane fun but burns too fast. 87 is also ok, just a little less response.

im in cali so we get sucky gas, id like to hear anyone elses imput on this.

DavisRx8

I too agree that 91 octane seems to burn faster than 87. Ever since I started using 87 octane, I average between 3-5 more mpg over when I used 91 octane. I haven't noticed a difference in quality - resulting overall performance - between Shell/Chevron and the "cheap" stuff (Beacon, Arco, Costco etc...) however. I thought there were federal and state regulations in place that dictate the quality of gasoline across the board...hmm.

shebam

Also got better mileage with my first tank of Shell 89 after using Shell 93 until now, but also put in the CZ Stage 1 during previous tank, so with 2 variables can't be scientific. No falloff in Stage 1 operation in going from 93 to 89.

rx8cited

djmano,

If you're going to become a Shell fanatic like your friend and I, you can get 5% rebates on Shell gasoline purchases (1% rebate on non-Shell purchases towards Shell purchases) by getting a Shell Credit Card. Check http://www.877myshell.com/ for more info.

I've been using Shell 87 octane with no problems for 4k miles.

rx8cited

cvan707

I've been doing Shell for years, got desperate, and had to go to Texaco. I handed the keys to my friend and the devil came over him, he was high revving and zigzagging for 70 miles and still I got better gas mileage than Shell.
I hear that each company has it's own sheet, or recipe of additives. The refineries blend in the additives to the recipe and ship it accordingly. Sometimes they blend certain additives that are not explicitly stated in some of the recipes, so legally they can mix for one company and it will still qualify for another. I'm sure some refineries try to mix a single blend that will qualify for as many companies as possible for easy liquidation (no pun intended). Business is business. Not sure what kind of repeatablilty we really get from tank to tank, even with the same company.
Still mostly do Shell because of the card and they're conveniently located after offramps. Will go to Texaco again, though.

hac

cavan707,
Whoever is giving you your information isn's exactly correct. I have worked at a Texaco (now Shell) petroleum termianl for over 14 years. To clear up a few things. At the refinery level all gas is created equal with the execption of what was called Amoco Ultimate or Clear. The only difference is what part of the U.S. you live in and what the EPA mandates for polution control in that reigon. Like oxygenated, conventional, 7lb to 13lb RVp, etc...
No additives are added in at the refinery level. All additives are injected at the terminals at various rates (cc's per 40 gallons or lbs per 1000 gallons) as it is being loaded on transport trucks. According to the Federal Gov. all gasolines have to be "additized". This additive distinguishes the difference between the Majors (BP, Texaco, Shell, Chevron etc...) The term used for a "non major brand" (Beacon, Arco, Costco, Speedway, Racetrack, etc..) is called Generic gasolin but still has a additive in it. No additive can be used by any company until the EPA approves it. I strongly recommend a "Major" brand of gasoilne. These companys do alot of very expensive testing for bragging rights to claim the best gas for your car. They do not "share" this additive with anyone. They offer a "generic additive" for unbranded (aka gerneric, non branded) You are correct in stating that some companies additives increase MPG and performance over others. No matter how small the amount of improvement they can still lay claim a "better product". Some majors also change additives from a "summer blend" to a "winter blend" during the year. Unfortunately I can't post the test results of the gasoline we sell to 4 of the Majors and 9 unbranded companies.
( A Legal thing) Being that I can obtain test results and have insite to who is changing what and when, I can recommend that I would use the following brands in the order listed, Shell or Texaco, (which use the same additive east of the Mississippi) Chevron, Citgo, & Amoco/BP. Keep in mind that all the majors are always trying to improve ther additive and results on who has the best can change year to year. Stay with a "major brand". Look in a owners manual of some really high dollar sports cars and they will "recommend" by name brand what gasoline to use ( all majors). These car makers test branded and unbranded gas as well to see what does best in there vehicle.

rx8cited

Hac,
Thanks for all that info. I usually use Shell, but when the owner opens late, I have to the Mobil across the street. Mobil's a major brand and was not on you list - I'm just curious why.

If you own a RX-8, what model do you have and what octane Shell do you put in it?

Thanks,
rx8cited

emailists

I once heard someone on the Probe list say that SUnoco Ultimate 94 was the only gas that actually had more energy than others. I didn't see sunoco listed as one of your choices. Also in my probe I went from various 91 or 93 octane to Amoco Ultimate and found I got better gas milage- and a precieved boost in performance.

Booster MPS

great post hac

hac

I'm sorry is I left out a Major or few. Mobil/Exxon, BP/Amoco, Chevron/Texaco, Unical/ and partners, Shell. All are Majors, meaning world wide players in the markets. Citgo is well on it's way to becoming a major also. If you choose a "independant/unbranded" and your happy, then stay with them. I personally will only use a MAjor Brand, any major is fine. As far as octane goes, in the 14 years I have seen the test results I can safely say that over 50% of the 93 octane gas sold by ANYONE, Major or not could be marketed as 94 octane. The Local States mandate that to market 93 octane it MUST test out in a State Lab at 92.5 or above. In order for refineries to be on test they refine at a higher octane to avoid MAJOR fines. The higher octane rating can also apply to 87 & 89 octane as well. This facility has never had a 93 octane test come below 93.5 in a LONG time. I have seen it as high as 93.9. Perhaps when you find a "premium gas" that you think has more kick/ performance it's because that perticular batch the refinery made was actually a higher octane than what you were previously buying. What I would watch out for is "non-majors" that add Ethanol to boost the octane. You can take 6000 gallons of regular 87 add 650 gallons of Ethanol and presto...you have 93 octane. Yes this is legal to do and no I cant say the ones that do it but there is a NICE profit in it. You would be suprised too. Again I would personally (again, MY PERSONAL opinion) recomend staying with a Major Brand. If anyone starts telling you "detailed info" (which I have not) on gasoiline they are most likely passing on "rumors". ANYONE in this side of this industry has to sign confidentialy agreements punishable by termination and or jail time. Any Info I give is public knowledge IF you know where and what govt. agency to look for.

hac

Rx8cited,
I got my wife a Velocity Red GT added a RX8store catback and a K&N intake. (because I liked the post I read about them) Sound very nice and performance gains are ok. I use Shell conventional 93. Mobil is fine, we don't have it avaible in South Ga. and North Fl.

emailists,
The higher the octane the hotter the burn/combustion, hence more power (in certian vehicles). Use caution...if the car maker recommends 87 then use 87. It's not a "wives tale" you can dammage smaller cylinder engines. The 2003 ZO6 I have states to use 93 so I use 93. The engine components are made for the hotter burn/combustion. For the record...I tried to swap cars with my wife and she would have no part of it. I WILL get mine own 8 next year. Just waiting to see if Mazda comes out with a little something extra for the 8. Maybe if someone hears of it they will post it.

Trx8

I just hit 19.2 MPG with Shell Regular. I had coincidentally filled up on Shell before reading this post. Given the balance of city-highway, I had expected 18 MPG or less. I changed my driving style about 1/2 way through the tank, minimizing granny style for city acceleration (shift at 2K max) and trying to shift in the (2.5K-3K) range. Previously I didn't recognize the potential for a value-added from the major gas brands.

I may sign up for the Shell card rx8cited has in his post above.

<2004-02-29> Next tank from Shell regular was 19.7 MPG and was the full range of driving conditions, including two passes at Driver-Ed sort of manuevers in school parking lots. I think I have started to realize some weak but distinct engine noise at acceration (I am not sure what it is) during the 3rd tank of regular and just put in a tank of Mobil Premium per the 1-in-4 approach to switching between Regular and Premium. I will see if the faint noise goes away with the Premium.

<2004-03-06> The Mobil Premium tank got 19.3 MPG, the distinct noise at acceleration went away with the premium, and now I have a tank of Shell Regular, mixed with the ~1/4 tank of Premium. Same mix of city/highway driving, but without Driver-Ed type driving. No noise during acceleration from this mix.

<2004-03-17> The Shell regular tank was 19.9 MPG, no acceleration noise yet, but last time it appeared on the 2nd or 3rd tank of regular.

Rotary787

It is my personal preference, but I wouldn't shift a rotary at such a low rpm (on a regular basis). I assume when you say shift a 2k, that refers to shifting such that you shift out of the lower gear at 2k and into the next gear at around 1.5k. I think lugging a rotary is very bad for it. Again my personal opinion, but I think the savings gained in fuel economy are offset by engine reliability. Assuming I don't care about accelaration, I try to end up above 2.5k in the final gear most of time, unless I am going downhill were I will go as low a 2.0 ocassionally.

This may be a wives tale, but this is my 3rd rotary and it has worked well for me. Most of my other cars (260z, honda accord, neon) mid to high reving cars and up shifting at ~ 3/4 torque rpm worked well (Never an engine problem). My last car was v-6 eclipse (very low torque) and it could be shifted almost anywere.

Chuck

Trx8

Yes, I agree that shifting at 2K is to be avoided. My sense is that the low RPM accleration is bad for the engine and may actually hurt gas mileage. Since I have an AT, it shifts when its ready, and in the city my accleration profile is bounded by the cars in front of me .. if they acclerate slow the AT shifts to next gear earlier than I would want. At times I will shift to manual mode just to maintain a higher reving gear.

My commute is 6 miles of ~urban driving, so my car spends ~half the drive warming up. Currently I try to acclerate such that the next gear starts above 2K RPM.

Doctorr

Mr. Hac, I salute you...

I am the guy at the other end of the pipe! I work for a Shell refinery, and before that, Texaco, for a total of 24 years.

We send the raw gasoline to the terminal with no additives, we only control octane, vapor pressure and 'drivability'. The terminal adds their magic just as Hac says, the Shell Optimax trucks get the top-of-the-line formula.

(Link to a previous discussion of fuel quality)

I agree that alcohol is 'cheating' in this business - since Lead was eliminated, we have to blend really expensive 'high octane' components to make decent gas, but they (off-brands) can just blend up some crappy components into a mix that tests out at 85, they can add a load of alcohol to meet the octane specs.
You get less MPG, less peak power, and other nasty effects.

Even though you are over two thousand miles away, it's good to meet a fellow '8 owner who can put the forum on the right track!
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doc

BARK

Just a quick observation - I'm running 89 Octane, and getting about 23 mpg (US) in highway driving.

I wouldn't buy an RX-8 just to shift at 2k - though I might be back off a gear to keep steady-state rpm below 3750.

Cheers

Rotarian_SC

I find that I get increased performance when I use Sphinx Racing gas from the pump. Sphinx is the only pump racing gas I have seen though. We have like 1 Shell in our area (30min away) so I usually wind up using Sphinx, Phillips, or BP. Would use Shell if I could...