I'm pretty sure that some knowledgable folks posted a while back (~1-2 years ago) that the RX-8 has a fuel cutoff if the car is in gear and you are coasting so that the wheels end up driving the engine. If you put the clutch in while coasting the wheels can't drive the engine and fuel must be supplied.

Besides, using the brakes only for long downhill stretches is pretty unsafe.

 

I don't know if this has been said yet but try putting in more air in your tires, but not to the point of overinflation. I think 35PSI would do 1-2 MPG than 30 PSI in a tire.

Also, if you have a stock airbox, changing out your air filter once a year would be another added benefit to getting better MPG.

Altho, i have to say your driving habits + road conditions will dictate what MPG you will get the majority of the time

 

That's exactly what I wanted to hear, thanks!

Will adding an MS or aftermarket exhaust improve mpg further since the afr is more leaner?

 

I think what really screws up these comparisons is two things, one Mazda based one driver based.

Driver based: As soon as you get on this car the poor mileage becomes very bad mileage quickly. The rotary is about 15% less efficient by design then a piston engine and they Mazda tuned it for the safety of the CAT seems to make it very thirsty.

Mazda Part: It would seem that Mazda has a quality control problem with Rotary engines. Some you can pound on and get close to EPA mileage estimates while other no matter how you baby them will never get close, I get 11.5 with a little aggressive driving to 13.5 city if I really baby it. Crap! Mazda will do absolutely nothing to fix this quality problem and will blame it on your driving, road conditions, weather, the alignment of the stars or anything else they can think of top avoid the cost of serving the car underwarrenty. It is pretty obvious that the Rotary has not been debugged before it was put into production.

In case your in doubt, a member of this board in NY was getting 11 mpg city and Mazda kept telling him it was his fault and this was normal. He finally gave up and accepted that the RX will get that mpg in his situation. After two year he decided to upgrade to a new RX, his mileage suddenly jumped tp 16 to 17mpg city driving the exact same roads with the same driver. Again it appears that there are a number of quality issues that Mazda is ignoring at the cost to the driver because it saves them a buck.

 

Just another fact about air filters. A high flow air filter can increase HP but will not help gas mileage. New cars us a system that monitors the amount of air entering the engine and based on several other facts delivers the amount of gas needed for the volume of air. If your filter is more restrictive or dirty then less air will enter and proportionally less gas will be delivered. The end result will be better mpg at the cost of less HP.

 

No it will make it worse since when you put an after market exhaust you usually run richer.

 

I didn't know about the fewl cutoff, that does sound clever. I guess it might compensate for the deceleration caused by wheels driving the engine.
As for safety, it depends on how steep the hill is. I was thinking of the sort of gentle slopes you get on motorways & A-roads.

 

Dont drive it.....

 

I've found the biggest impact is cruising at a lower speed on the highway. I cruised at about 65 for one tank and got ~25 mpg, compared to the usual 75-80 which gets me a shade over 21 mpg. Around town, try to keep as constant a speed as you can. It'll take a lot less gas to cruise down the street at 35 rather than speeding up to 55 and having to brake every time you come up to someone going slower

 

I thought the same thing, and I have only filled up once since getting it, but I seem to have a 1-1.5 mpg increase in my fuel economy with a drop in K&N filter. My first tank after installing it was better than my highest before. This was 90% hwy driving, and may not do as much if it was stop and go. Fortunately, I have one of the 8's that actually get the EPA estimate.

 

I might have to try the K&N drop in filter. Since it breathes better, I wonder if it also lets in more debris which would of course be bad for the engine. As far as cruising more slowly on the freeway, I live in LA and average about 25 mph on the freeway, so thats not the problem. I'm getting about 18 mpg combined. I just installed a Greddy exhaust so I'll have to wait and see if that effects mileage any. So no one has larger diameter tires? How about the opposite? Anyone noticed a drop in mileage when they installed a smaller diameter tire? I think 245/40/18 is a smaller diameter, but I'm not sure by how much.

 

One thing worth mentioning is that the current EPA mileage tests are very dated and do not represent the driving public any more. (That's why they're coming out with a new test). The current highway numbers represent a test loop that has an average speed of 48 mph and a top speed doesn't even exceed 60 mph.

 

yes there were several threads on this...

 

^^yeah there's a website link floating around in one of those threads about updated EPA estimates. Or you could just google for it.

Just ordered my K&N last night at Pep Boys. Looking forward to your results, MonkeyBoy88.