OK, here's the summary from this forum so far. They are mostly first and second tank results from all across the country, different driving styles, etc. YOUR RESULTS MAY VARY.

Rx-U-UP 16.1
RX-U-UP 16.6
Zoom49 18.9
Gettingan8 18.0
JR_TX 19.0
RX_NUT 18.5
RX_NUT 18.5
Rotary_It_Up 18.1
8-Wannabe 17.0
RXeightr 21.4
Ahura 20.2

Average = 18.4
Range = 16.1-21.4

The average is really an estimate because we don't have all the data here like the gals used. I just took RX-NUT's 18-19 mpg data for two tanks and duplicate his average.

But this at least gives all of us some interesting results. The 14 mpg claimed by a forum member from Japan appear to be an outlier a not a true indication of the mpg.

So do those last two guys work for Mazda? Just Kidding.....really!

 

The area around the shifter gets so warm because the engine is much closer than in most other cars.

 

The Insight recommended fuel is regular unleaded. Since, as you say, going from regular to premium in such a car won't improve gas mileage, then there must be some other explanation. I would look at: Changes to driving style or conditions; break-in period; statistical accuracy (as in, for how long and precisely did he take measurements?) I would expect the cause for mileage improvement will be found here, not due to the change in fuel grade.

 

I checked with my dad on the whole octane thing. He was a mechanic in the war so he knows about this stuff. He said for me to do what they did in the war: Put in two gallons of kerosene to each three gallons of gasoline. If you still worry about the octane, dump in a few mothballs or naphtha flakes. I tried it and got a stream of grey smoke. He says this means I got it just right. I'll post a test report later.

 

Shall I call for Roadside Assistance????

 

You Guys must be doing something wrong.

I got just over (30) thiry miles to the gallon on the first half tank...but then the wife said she was tired of pushing it and wanted back in the car. It dropped a bit after that.:o

 

You own a twin turbo RX-7 and you're concerned about your impact on the environment? :D

It's not that simple anyway. Fuel usage is up but NOx emissions from the RX-8 is going to be lower than probably even your CRX. Admittedly *** emissions are up in the rx-8, but they don't cause a big brown haze and acid rain do they?

-pete

 

Mr. Wannabe, what exactly is it you are trying to do?

You say you don't want to burn Premium (because why?)

You maintain that you are not just being cheap.......

Then you tell us you and your dad are using an old 'wartime' recipe to make your own gas? From kerosine? With an octane rating of maybe 10?

Can you let us know what your aim in all this is? I am lost......

And be very careful mixing moth-***** into your mixture, that old fable started when moth-***** were made of Naphthalene (which actually has a pretty good octane rating, but grows into crystals in your fuel system, kind of a kidney stone for your car!) They haven't been made of that for many years, and the new ones are made of para-dichloro-benzene, which will not burn, is toxic, and the EPA will lock you up if they find it in your fuel.

Otherwise, it's your car, go for it!
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doc

 

Geez, doc... lighten up. I reeled you in hook, line and sinker with that one. You need to relax and enjoy life just a little bit more. At least boowana recognized the humor of my tongue-and-cheek post. (though my dad really did do this during gas-rationing days, the moth ball lumps might tend to clog up them new-fangled fuel injectors thangs.) And with a note of seriousness underlying the whole thing, I am attempting to illustrate the futility of anecdotal information in answering a systemic question. These "my friend he..." type answers don't cut it. I want to see real data backing up any allegations that premium octane has any real benefits to this car. Thus far I haven't seen it.

 

rpm_pwr: I owned a 93 RX7. One of the reasons I don't have it anymore is that I could not stomach 11-12 mpg. And it wasn't the money either. The other is that after I had a local rotary specialty shop install my oversize radiator, I could not get the radiator level topped off, saw remnants of combusion in the radiator fluid, and could hear sounds during boost that said something was wrong....damaged seals. So faced with a rebuild after dumping in 5K, I bailed and sold it. I bought it in spite of researching and understanding all the shortcomings of the 3rd gen, especially the 93's.

Yes I do understand your point about NOX emissions because that's why all the major manufacturers had options on the Wankel, low NOX. They didn't see any way to meet the future strict NOX emissions standards with standard technology available at that time. I don't know how it compares to the CRX-SI but that would be interesting since it is now 13 years old and I just had it smogged and have the data. The RX-8 is probably way better given today's standards.

8_wannabe: I'll have to check with my friend with the Insight on that and how everything resolved for him. You are right about regular being the recommended gas. He was one of the first owners and was driving the same route from Santee to Sorrento Valley everyday. He's the type of guy (electrical engineer/programmer) that is very careful collecting and interpreting data.

So did you have to get a permit to burn that stuff?

 

Well 8_wannabe, you are the 2nd lowest mpg on my list. Of course that could be due to driving style and not all that significant until we've collected more data and somehow normalized for your driving style. That's why I suggested you try a tank of premium every now and then to compare.

And maybe you have some problems with my example since you are correct about Honda recommending regular (I checked). But be careful when you ask for data. This guy with the Insite is extremely **** and I know he has lots of data on this, being the mad scientist type that he is, lol.

I just need to recheck with him on that story because it was years ago. The point I was making is that the RX-8 was designed to use premium, even though the electronics will compensate and run with regular. But what if you're out on an extremely hot day, AC on, the car loaded with two people, humidity and altitude just right and you're hitting red line when you cause the car to detonate and loose an apex seal. Or the knock sensor just isn't fast enough under extreme conditions. There are lots of RX-7 owners out there that this has happened to even after lots of succesful miles, given the right extreme conditions. The 20 cents a gallon is cheap insurance. Why experiment with your 35K dream car? Why tempt fate?

Or how about this arguement. One of the reasons you bought the RX-8 was for its performance, handling, smooth acceleration, etc. Will you admit that running with regular has to lower the perfomance somewhat? They've got to be retarding the timing when the knock sensor senses impending pinging. And retarding the timing will at least mean lower acceleration if nothing else. Heck, most RX-8 owners probably would consider performance increases, not decreases. But it is your car and this does give all of us all something to jump up and down about.

So how many mothballs to the gallon......

 

8_wannabe. The 2nd quote here is the more important one. No I don't have tons of data supporting this, but you don't have any to refute it I bet. Besides we all agree with you that it's a waste to run higher octane gas than your car requires and it doesn't product more power or economy. But the last quote is logical and makes perfect sense to me. As an engineer I would certainly do extensive research if I was using this statement to design a product, but that isn't the case here. I think the RX-8 manual is just telling us that if you have to put regular in for some reason, the engine management system will compensate for that.

This one is about the PT Cruiser, Turbo. For best performance, 91-octane fuel is recommended, although the engine will run on regular with some power loss. Modern engine management systems with advanced knock-sensing capability can adjust the timing to compensate for the octane rating of the fuel.

This next one is the most important from omegamotors.com. Now I don't know much about the source but I can't really find any data that refutes this and all of this makes perfect sense and is logical:

If your car requires high-octane gasoline and you habitually use regular gas because the engine exhibits no sign of knock, you’re outsmarting yourself. Most modern, computer-controlled engines include a knock sensor that detects knock and retards the ignition timing, causing the spark plugs to fire slightly later in the cycle. This typically prevents abnormal combustion and knock, which allows vehicles specified for premium fuel to run on lower-grade gasoline if it is all that’s available. While this removes the immediate hazard, it’s a bad idea to make a habit of running a vehicle on gasoline of lower-than-recommended octane. Retarding the spark causes a richer fuel/air mixture, which decreases fuel economy, increases emissions, causes the engine to run hotter, and reduces the longevity of both the engine itself and the catalytic converter. The money you save by pumping low-grade fuel into a car that demands higher octane is lost anyway, in decreased fuel economy and possibly gradual damage.

 

Thanks, Fred. At least you're backing up your argument with some engineering detail. I couldn't find this quote at omegamotors.com, all I found was info on selling cars. Where exactly is it? Obviously I need to learn more about knock sensors and timing. If there's a problem with lower octane, that's where it'll be. You've at least introduced enough doubt in my mind that I'll burn premium while I research this. As I've said, it's not the money savings, it's doing something for no known good reason. So I'll keep investigating.

 

8_wannabe:

Here it is: http://www.omegamotors.com/enjoy/gas...soline_06.html

Yes this one sums it up pretty good I think. Even with the knock sensor on the RX-7 you couldn't get away with regular so the technology has really come a log way in 10 years. I seem to remember that the stock knock sensor was notoriously slow and that lots of people were using faster, higher quality after market knock sensors especially if they had any mods. Lots of kids just added a high flow cat-back with an improved intake without changing the fuel maps, only to blow their motors after many miles without incident.

If you run premium on the next tank then we'll have our 2nd data point for you. It's only about 12% more in cost but will let you sleep easy until you find other data to contradict conventional wisdom out there.

So do you ever get over to UTC for lunch? Would love to see your car sometime.

 

Yeah, yeah, you got me good......!

Geez, 'Owned' by a wannabe!

Yoink.....time to go back to my beer!
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doc

 

It's all that emmissions crap....anybody gut their cats yet?

 

Here's an update with one new data point. I'll try to update this for awhile (maybe every Monday?) if I get some new data and there is interest.

Rx-U-UP 16.1
RX-U-UP 16.6
Zoom49 18.9
Gettingan8 18.0
JR_TX 19.0
RX_NUT 18.5
RX_NUT 18.5
Rotary_It_Up 18.1
8-Wannabe 17.0
RXeightr 21.4
Ahura 20.2
JR_TX 20.8

Average = 18.6
Range = 16.1-21.4

 

Thanks for keeping track of this; I'm in the same boat you are. The more data points I see over 20mpg, the more tempted I am.

Sam

 

Yes and now if Mazda would step up to the plate and say something about that AC and heat problem, we'd all feel better. I think they will soon given enough complaints about it. Seems to be easy to resolve with insulation or maybe some sort of radiant barrier. They must have seen this in the proto stage of development because I know they typically do a lot environmental testing. It will be interesting when the dealers call Mazda to ask about this. But on a more positive note, the mpg's are looking very reasonable to me and a major improvement over the RX-7.

 

Let's see, in terms of RPM that's about:
1 to 2: 3500 RPM
2 to 3: 3500 RPM
3 to 4: 3000 RPM
4 to 5: 2700 RPM
5 to 6: 2700 RPM

WTF, I wouldn't even want to cruise at 2700 RPM, let alone shift up to a higher gear. That would mean cruising in 6th gear as early as 2300 RPM (46 MPH). Based on this engine that's way too low for comfort. If that's what they used to get mileage estimates, no wonder it doesn't seem to mesh with what many people are seeing in real life.

As for me, every tank seems to be improving the mileage. Most recent was 18+.

As for comparisons with an SUV, I'm also not too happy with mileage going down near that range. But it seems to me that my mileage at the worst is still better than most SUVs at their best, and I think I can live with that.

 

shakes head..

Just for comparisons sake from the piston world, what kind of fuel economy does an s2000 get? I've heard from Canadian owners it's about 12-13L/100km.. So that would be about 18mpg US?
If that's the case I think 18-20mpg from the Renesis considering the power output is fair. Also these cars are still breaking in, I suspect the fuel economy will improve after break in.. OR it won't since you will be able to rev to redline then. :p

 

From the s2k forum I've seen reports of as low as 10mpg (racing)and as high as 22~24mpg tops (highway) driving grandma style

 

Check this out and draw your conclusions on it. Myself, I'd use premium on the 8

 

The S2000 can get quite impressive gas mileage when driven reasonably:


http://www.s2ki.com/forums/showthrea...threadid=67021

http://www.s2ki.com/forums/showthrea...threadid=92693

 

I just finished a 900 mile round-trip (new grandson born Saturday!) and averaged about 22 mpg on interstate (cruising 75 to 80). I haven't let the tank get too low but the first quarter tank on the gauge seems to drop fairly quickly unlike other cars I've had that seem to hang on full for quite a while before showing consumption. The 16 gallon tank should get you over 300 miles regularly on a tank with mostly highway driving.

I agree with that I didn't buy this car for its mileage - I bought it for it's handling and it is a dream. My son drives a BMW M3 and we traded rides yesterday. His acceleration (on the M3) was incredible but he was jealous of great short throw "click" on the RX-8 shifter and the steady "give me all you've got" acceleration and feel of the rotary.

The 7 1/4 hour trip (each way) was pretty comfortable (love the seats). It was at least comparable to the Nissan 240 SX I've driven for the past 8 years. I hit very, very heavy rains coming back in to Cleveland but the car didn't seem to notice at all. The wipers had a little trouble keeping up with the torrential rain but the tires stuck like glue and gave a very confident feel.

More later. Hope the mileage info helps.