I had a 2004 RX-8 that I used as a daily driver for almost 4 years. More often than not, I was stuck in traffic. As such, running lower revs with a lot of stop and go, I felt that there was no benefit to running high octane. I used 87 octane most of the time and never had trouble with knocking or pinging in the engine.

When the car was new, I used 93 octane and gradually experimenting with reduced grade of fuel. If I knew that I was going to do spirited driving, I would fill up with 93 octane. This served me well throughout the ownership of the car.

I always had the car dealer serviced and they never said the there was undue wear and tear on the engine - no keaks, no CEL, nothing. I gave up the car with 65,000kms and it was still running like new - and I put that car through everything - winters -30 degrees C, summer +30 degrees C, spring, fall, occasional redlining, stop and go driving, AC on, AC off, etc.

Unfortunately, I did not have a trip computer and I was always too lazy to keep accurate mileage logs, so I can't comment on fuel economy. My new ride has an onboard computer and tracking my daily use the last couple of weeks, I found that lower octane does indeed result in slightly higher gas mileage.

 

26-27 mpg on 87 but babying it, No AC since I drive at night. IF it gets hot then I turn on the AC or open the sunroof. Not much traffic at that time so can go slow, ie48-58mph, country driving, ie driving from one city to another. '06
That's low since I ride a bike and a 4 banger that gets over 35mpg
Bigger / larger tires also help in getting more mpg
My 4 banger had 14x now has 18s.

 

$82 from Empty to full.... total km's driven till empty... 387.

So that would be umm... over $5/gallon and about 240 miles to a tank.

roughly 15mpg all the time no matter how i drive.

And on top of that i pay $130 a month in insurance for a 10 year clean driving record. And $344 a month car payment for 4 years (I put $10,000 down payment).

Total cost of driving per month: ~$800

Living in canada and paying out the *** for everything... priceless.


Also, pre-det in a rotary isn't near as bad as a piston engine... I'm not sure how it would be bad at all besides loss of power. It's not counteracting any forces as it would in a piston engine.... piston engines that ping are trying to force a piston downwards before its made its TDC, as well as before the valves are properly closed.... pinging in a rotary would mean its not "TDC", but it will still send the rotor in the correct direction, but not at it's optimal ignition location for maximum power or compression... I doubt there is as much stress if any in a rotary as people might think when pre-det occurs.. Just less compression and less power.

 

gas here just hit $4.90 for shell premium

unbelievable... gotta love CA tax

 

I wish mine was 130 dollars a month....right now because i moved to alberta i pay 280 a month!!!!And this is with a clean record as well(albeit i am 20). If i would have continued to insure it in Saskatchewan it would have only been 90 dollars a month..what a joke.

 

Had to comment here. I'm new to the RX8 world as I just purchased a 2004 for my son. I had heard that the gas mileage wasn't very good and tried to discourage him, but due to the design of the car it was either an RX8 or another Saturn Ion for my son and he really wanted the RX8. I picked the car up in Temecula, CA and drove it home to Regina, SK. We drove 80-85 all the way along I-15 and averaged 22-23MPG. I thought this was pretty good considering the speed, terrain and that its an automatic. Not sure how its going to be around town, but we'll see.

 

i ran 87 in my last tankfull and netted 20.3 mpg in purely city driving, with the air on for at least two days.

 

8.7 mpg.

beers

 

i just don't get it..

 

I've been averaging about 18-20 mpg with half freeway driving. if i was mostly city i could see the 15 mpg or so.

 

My gas mileage has been deteriorating...
My light comes on with approx. 10 Liters left in the tank.
270kms was the best i've seen this spring/summer and it's been gradually getting worse, to the point where my last two fill-ups were at 240kms and 230kms...

I'm sure the dealer will just tell me it's the way I drive or the wider tires... It really doesn't matter if I drive the car hard or not :\

 

that's about where i used to average, 240 miles per tank or less actually, in city driving. but i just got a reman and i think i'm getting a little bit better mileage!! i'm pushing 270 right now and my gas light just came on. that was 70% highway though, but the other 30% was pretty spirited city driving.

last weekend i did all highway driving, a little 18-wheeler drafting (safely of course), mostly 6th gear under 70mph, and only one or two 3rd gear drops, and i got over 310 mile on the tank! average was 23.28 mph! yes, 23.28. i had never gotten over 20.8 on my original engine, so 1st road trip with the reman lookin' pretty good!!!!! oh, i ran 89 that trip. i usually run 87, or did with my original, but having been using 89 lately. oh, ac on the entire time, but windows up. i bet i could have broken 24 mpg if it weren't so damn hot in tx!

 

Thats right in the range that i would get. I drive mostly city and would regularly get 240 to 250 to a tank (km's). Just this last week i changed my spark plugs out for new ones and my mileage went up to 310 km's per tank with similar driving. MY car had 55,000 km when i changed the plugs out and i am unaware if the previous owner ever changed the plugs, i doubt it.

 

Erm... ask anyone with a turbo FC or FD about detonation. Detonation tends to be even more catastrophic on a rotary engine, becuase apex seals are a lot less tolerant than connecting rods.

 

I still don't understand how pre-det will be more catastrophic on a rotary engine then a piston engine.

In a piston engine pre det is counteracting against the piston/rod/crank/valves because the piston is still trying to go up when the combustion is trying to send it back down.

In a rotary the pre det isn't trying to send the rotor back in the opposite direction, It's just not making optimum power at it's proper compression... the combustion is still forcing the rotor in the correct direction.

Plus you can't compare turbo to NA. While the renesis engine does create a lot of heat, the older turbo engines create more heat and have different cooling channels then the renesis. I would think the apex seals in older rotaries will have issues with a much more drastic thermal expansion and un-evenness of the chamber then renesis now.

While i would agree that a connecting rod is stronger than a seal. And i'm also not trying to say that pre-det is cool either.

 

WO HOO!!!

 

Got 20.18 over my last two tanks with mixed driving with liberal AC use. Seems pretty easy to do, I put it in neutral anytime there is a hill and coast down it. Coast up to red lights and after redlining it in 1st and 2nd I quickly go to whatever gear gets me between 2-3k rpm (bought a sports car not a prius so I'm gonna use it). Doing this has given me a bump of 2mpg on my daily commute.

 

I thought using 87 octane was bad for our cars. Doesnt the manual say preimum only?

 

I could be wrong, but I believe I've read on here that no fuel is delivered while coasting in gear. Therefor you are better off staying in gear than going to neutral. Maybe someone can clarify this again.

edit - relevant discussion. https://www.rx8club.com/rx-8-discussion-3/there-any-harm-coasting-59557/

 

Read through part of the thread you listed. I typically average 18.25mpg and now I’m up almost 2mpg so I’ll stick with the neutral thing. Not like I have any winding roads on my commute anyway. Down a mountain road you’d need to be in gear but a straight shot with 5 car lengths in front should be fine.

 

My light came on just now at 160miles haha..... damn turbo makes my foot heavy.

 

Switched to regular a few weeks ago, and I think that I've noticed a slight improvement in mileage (~1mpg consistently). Hopefully the AccessPort will improve it further!

 

I got 40.5 mpg my last tank and I think I could have done a little better. No I don't have a hybrid and yes it has 4 wheels. It wasn't a rotary though.

 

My 8 just surprised me with 23.8ish...this was driving between 50-70 most of the time, and occasionally in the 80s with some heave accel around Baltimore. ~180 miles PA to MD. AC on and off and premixed with Lucas oil UCL (amount recommended on bottle). Since I have been in Maryland my gas mileage went up by about 2 mpgs, due to PA mountains "hills to some".

 

well My driving is 100% city and I got 14mpg. I will be taking a 100% interstate trip soon and report how well it does.