I hate to start a new mileage thread, but I just wanted to brag that my wife hit 27.175 mpg in my rx-8!

we were driving from Phoenix to Missouri. She drove from Tucumcari, NM, through the texas and oklahoma panhandles, and all the way to Liberal, Kansas. this was at night. the speed limit varied in each state from 60mph (in Texas) to 65 mph (everywhere else). she kept the cruise control set at an indicated 2mph over the limit. (we were trying to save gas) she also had to slow down for many small towns along the way.

she went 214 miles on 7.875 gallons of 87 octane shell fuel

 

Let's hear it for Regular Unleaded!

 

wow, 62mph on cruise

could you hear your 8 *pleading* your wife to go a bit faster??? :D

 

I've gotten 27mpg going 65-70mph on cruise with the A/C on and the radio blaring. Most cars are not designed to get good mileage over 70mph, and in reality, its starts falling off around 65mph.

 

I've got 27 also on my 3rd gen RX-7 with cruise control set at 65 for looooooong highway stretches

 

I just got 26.7 mpg cruising between 70-70mph... tried taking a pic of the needle on 1/2 at 200 miles but it didn't turn out too good

i also got 25.8mpg on the way home despite being caught in a 30 mile traffic jam for the better part of 1.5hrs trying to escape DC rush hour traffic

 

Yeah, but everyone knows it's all downhill between Phoenix and Missouri

 

Inside teh gas cap, doesnt it say to use only Premium gas?

I never ever thought about putting anything less than Premium in my RX8, I dont even do that with my trucks.

 

actually, I double-checked; this tank was 86 octane gas (thank you, new mexico).

my take on octane is that different octane gases burn differently. with a normal engine, the timing of the spark is set for a certain octane. with higher octane gas, the spark can be set 'advanced'. if lower octane gas is put in, most modern cars have 'knock sensors' which will detect pinging (precursor to detonation) and retard the timing to compensate. so the net effect in a normal engine is that lower octane gas in a car set up for 91 octane will just result in less power, since the computer retards the timing.

now in a rotary, the story is a little different. there's no pinging in a rotary, just detonation; the gas ignites at the wrong part of the rotor's cycle, most likely blowing out an apex seal.

so I consider low-octane gas dangerous. anytime you get in a high-heat, bogging type situation, you run the risk of blowing out an apex seal. but I figure if I drive conservatively, and keep the revs a bit higher than normal in cruising (Like if I would normally shift to 5, keep it in 4) it's probably ok. and I avoid hard acceleration and shifting at the redline. (I try to keep the revs in the middle, not too high, and definitely not too low).

I generally just use low octane to save a bit of money on long road trips, when I know I'll just be setting the cruise control on the highway. in fact, on the way back from missouri, once I got into new mexico where I knew I'd be going up the big hill into albequerque, I put in 88 octane (choices were 86, 88, 90) just to try to be a little bit safer.

some people have been reporting better performance and better throttle response on low octane gas. I consider the performance difference to be unnoticable without instruments or a way to measure it. then I'll go on to say that in phoenix, one day my dash external temperature display was saying 119 degrees and I still had 87 octane gas in the tank after a road trip, and the car just 'seemed' to run like crap, and this was just cruising down the highway. it felt like if the car was breathing, it would be wheezing. the next day, just as hot, with 91 octane, it ran normally.

 

the renesis has a good knock sensor - using low grade gas is not a problem...

hell, on 89 octane i'm raising the a/f ratio by a .5 point and adding 5 degrees of iginition advance and haven't had a problem in a year now with it even hitting the knock sensor

 

cool, I wasn't sure if it had a knock sensor or not.

how can you tell if it tripped the knock sensor?

 

The car will push back on you kinda like you hit the brakes. Its really just the engine pulling tons of timing out. Ask me how I know... Stupid mazda required a reflash to do the recalls on my car... now my tuning is all hosed.

 

The best I got with a tank was just over 24 mpg in constant 85mph and over interstate traveling down the Carolina's and Georgia to Florida with the a/c blasting. I have tried using less than premium, but I can feel the loss of power and I get worse fuel economy. I think the low grade fuel may be resulting in unburnt fumes that leak into the cabin- causing delusions by the passengers and driver.

 

damn! i can't go that many miles on twice as much gas.

 

LOL :D That is actually just the car. It is mystical.

 

And I thought I was doing good getting 24 mpg on long trips. Of course I was doing 70-75.