I wasn't a believer until now.

My usual fill-ups occur between 200 and 220 miles.

Last tank I 'installed' 13 gallons of Chevron 89 Octane.

I'm at 24x miles now, and 'just' under 1/4 tank remaining.


I'll let y'all know how many gallons it takes to fill tomorrow morning

 

Were the driving conditions any different? More city/less highway, or vice versa?

 

Any engine knocking like I experienced? (it sometimes doesn't show up until after a few fillups) Also, lower octane, for me, resulted in decreased performance (i.e., slower acceleration). I know many people here don't share the same experience, but give us an update after a few more fillups with your general observations, beyond just the mpg.

 

The conditions were about the same - i had 'one' longer than usual freeway adventure - but nothing so different than my until-now-best tank, which was 20.3mpg.

I can't 'feel' any pinging...nor hear it. Car seems strong...but my AssDyno™ hasn't been calibrated lately.

 

i thought these cars only took premium. i just afraid of detonation/pinging.

 

I would be kinda scared to add lesser grade fuel, but if it works out for you...then saving $$ is always a good thing.

I only use 93 (we dont have 91 here in Central FL) and I'm getting 250-260 miles between fill ups. I wish we had 91 so I could save some $$ too...

 

I did the same test with two tanks in a row and didn't notice any difference in mileage, but I did feel the slight lag in acceleration. I'm using 93 (we also don't have 91 where I am in TX) and I plan on sticking with that.

Disclaimer: I very rarely drive on the highway so this is based on all city. It may change if highway driving was involved.

 

what is your 'freeway to city street' driving ratio?

 

Silly question here...

But I noticed the Manual says "Premium" gas recommended.. what octane is considered premium by Mazda standars?

I always thought that indicated the top available (93 octane) but it didn't occur to me that it might be refering to 91 instead. Here in SFl we have all 3 grades, 89, 91 and 93..

Btw.. dealer mentioned that thier owner has had his RX-8 for the last year or so and has only put in low 89, without any problems. He pointed out that Mazda 'recommended' premium not required. Though he did point out that if I went the 89 route, I should probably put in a bottle of gas additive every other tank or so.

 

The detergents and cleaners and what-not are the same in whichever Octane grade you choose - as long as each came from the same store...

e.g. Chevron 89 Octane (which I have in the car now) has the same 'techron' the 92 Octane has.

 

Interesting article from USAToday (dated July 03) discussing this subject.

1 1/2 years old I know..but still interesting.

Note that their definition of Premium is any gas with 91 Octane or higher.

http://www.usatoday.com/money/autos/...emiumgas_x.htm

 

wait.... so how far can the 8 go on a tank of gas? and how much, is each fillup, generally, and price of gas... im looking to get an 8 in about a month or so, so it would be nice to know these things before hand

 

This is from the manual:
"
Your Mazda will perform best with fuel listed in the table.

Premium unleaded fuel 91 [ (R+M)/2 method] or above (96 RON or above)

You may use a regular unleaded fuel with Octane Rating from 87 to 90 (91 to 95 RON) but this will slightly reduce performance. Fuel with a rating lower than 87 octane (91 RON) could cause the emission control systemto lose effectiveness. It could also cause engine knocking and serious engine damage.
"
I use 87 and haven't noticed any problems. Going from 0-60 in 6.1 Vs 5.9 isn't my biggest concern.
I get between 17MPG on short trips in cold weather to 21MPG on long trips at 75-80. No data on long trips at 55MPH :D Why would you even drive this car then?

 

Tried one complete tank of 89 octane and found no difference. I suspect that cancelling the variation in driving conditions, weather, etc. will take several tanks. I have noticed, however, that a single freeway trip of less than 100 miles total raised my average mpg by about 2 mpg compared to other tanks.

BTW, dmp, were you using 89 octane in your dyno run? And do we know what kind of jet fuel our friend who managed to get over 200 hp out of his RX-8 was running?

 

I went out to the car for lunch, and when I started the engine, I noticed the fuel guage was substantially lower than when I left the car this morning.

A quick stop at the fuel station, and 12.7 gallons later, I figure 19.77 MPG for the 251 miles showing on the odometer. In an attempt to cancell out variables in driving, I re-filled with 89 octane and going to try one more tankful.

I had 92 Octane in for the run...I think Warren may have had a sneaky-pete n2O bottle in his glove box

 

I tried 89...definitely felt a lack of power at higher revs. Normally there's a smooth surge of power that comes on after 4k RPMs...using 89, that surge just didn't come on. Didn't hear any pinging or knocking, but that doesn't mean that it couldn't be happening, especially at higher RPMs. You won't necessarily hear every ping or knock, and by the time you do, there could've already been serious damage done to the engine. And the rotary in particular is more vulnerable to damage from knocking due to its apex seals.

I suppose you could stick with 87 if you granny drive the car all the time, but if you plan on revving it to redline often, I'd stick with premium.

 

well, I'll granny drive this 89 tank, and check the results...

 

hehe you used "sneaky-pete" in a sentence...you are my hero for the day:D

 

I've been tracking every tank of gas since I bought the car (8000+ miles now) and have switched between 87 and 91, using each for five or six tanks in a row. I haven't really seen much difference. Mind you, winter fuel may be another variable that we have to watch out for.

I have a spreadsheet for all of the tanks, but it is at home.

~ Matt

 

Maybe next time you go to the dyno with the 89 to see what exactly a "decrease" in performance (from the manual) means.

From the Car & Driver article the M3 performance was down about 10 % (91 to 87 octane gas) & the Saab turbo was down 12%.

 

Can everyone give me what Range they get on average from a Full Tank?? Reading thru the threads, I see from 200 miles up to 250 miles, w/ more mileage coming from lower Octanes...
Anyone getting more than 250 miles between fill ups???

 

yes, last tank for me was 265 miles. But, as it was said so many times, measuring "by the tank" does not say much and is not a good method to determine mileage.

 

I have around 12k miles on my car. For the first several months, I maxed out at 200 miles/tank (didn't take it to 'E' obviously). Now, having broken in my car by now, driving more conservatively, shifting at or below 3500 most of the time, and, in dry weather, turning off TCS/DSC, I can get between 240-280 miles. I still wish I could get better, but I'm satisfied that there has been steady improvement as my ownership has gone along...

 

Those able to drive more than 240 miles on a tank, are you using Premium (91+ Octane) or lower grade fuel??

 

I think us RX-8 lovers warm our new babies longer, just to be sure, she's warm! Do what I did, warm the car, go fill the tank, go for a drive, enjoy the twisties, listen to the puuurrrr, turn some rev's, then go fill-up. I'll bet your MPG will be in the 20's. Warming up the car uses a lot of gas!!

my 2 cents.....but I'm up from 15-17 to 21-23....by measuring drive to drive w/o sitting in the driveway!!!