newport8

Squidward, you are right. Occam's razor holds true once again.

canzoomer

Actually the opposite.
I did not count the 2.5 tankfuls I have run with mods installed and active.
So far, using MY driving style, I have run 2 tanks on highway, and one half in city.
On the highway, where I generally run at 140-145kmh, I got just slightly better mileage than my previous tanks. About .5l/100 better.
In city driving, where I tend to rev higher more often, I got quite a bit better mileage, at around 1.5l/100 better.

As it is not a large enough sample, and as this study was on cars that are stock, i did not include my recent tankfuls.

I do not believe my mods will have a major impact on highway mileage, and for city mileage , while there is definite gain, that is dependant mostly on driving style.
The only areas where we leaned out the mixture was above 6,000rpm.
For this to be a significant factor you have to get on the gas and shift above 6,000 with some frequency.

If you drive more gently, and shift below that then i expect to see little difference in economy.

canzoomer

Exactly right. I ran one tankful on the highway, and kept rpm below 4,000 ( speed below 125kmh)
I got about 2L/100 better mileage than my usual speed of 140+kmh and 4,400rpm.

Another factor to consider on the highway driving is that just below 4,000rpm the secondary intake runners are opened, and fuel consumption will climb at an rpm range above that.

This car will make mediocre mileage when driven at speed limits, and with a gentle foot.

And horrible mileage when you go faster.

mngpao

Norton: the link I quoted was found at www.fueleconomy.gov

Sorry I didn't include it with my post. That URL is on the window sticker in the bottom of the border that surrounds the MPG notice.

norton

RodsterinFL: Based on the data provided, the correlation of .22 means that Octane has little to do with MPG. I tried a lot of different approaches in the regression analysis with respect to Octane because I know that this was a topic of much discussion. I could never achieve any result showing Octane measurably impacts MPG. So I cannot answer your question. From what I recall, I believe you were one of the major proponents of using 87 Octane and had originated a thread on this issue. Right??

norton

canzoomer: Sorry. My bad for assuming your response was post engine mods.

norton

newport8: Occam's razor Never heard that term before. Pretty funny. In case anyone is interested, here's a link for the definition, cartoon included: http://zebu.uoregon.edu/~js/glossary/occams_razor.html I guess for those people that think that the analysis showed ONLY what was obvious, then this is true.

newport8

In the statistical world, it's essentially leaving all those extra variables to your error term.

If you normalized MPG for % highway time and just plotted a simple histogram, I bet you'd get a standard bell curve. You might even get one without normalizing. I think the problem is that, no matter how precisely Mazda tries to build its rotary engines, there's going to be a some inevitable variation present, which will show up in a standard distribution of MPG, HP, or whatever. Some people will get lucky and get an engine that is at the top end of the curve. Others will be unlucky and get one at the bottom. But most people will get one at the mean, median and mode.

norton

newport8: Yes, I agree with you about the normal distribution. Hopefully this inevitable variation in rotary engines would yield only a slight variation in MPG, given identical driving and other conditions. It's hard to assess though, because as you said, the Standard Error encompasses a slew of factors other than %Hwy and Driving Style.

8_wannabe

It may seem obvious now, but there was protracted and heated debate when the first of us got our cars to look for other reasons in our different MPG results. The common culprit was ECU changes. We had no way to assess driving style until Norton put this together. STrange tho it may seem, it was not immediately obvious at the time.

Racer X-8

Um, in reference to the above Squidwardian quote, it is the pretty (doggon) obvious factors, those very things, that cloud the original persuit of determining the not-so-obvious factors that also affect mpg.

VIN (build date) <<--- most sought-after factor
Total vehicle mileage
MT .vs. AT
Aero kit / rear spoiler
Strakes
Front / Rear rotary accents
Color
Marital status

mac

I would love to see if distance traveled for daily commute is a significant factor. I have read several threads where a short trip in a cold environment will result in below average consumption. I travel 7 km all highway (except for a total of 10 city blocks with 3 stops). This was true, it would significantly skew the results since I would present as 90% highway but horrendous MPG. Ambient temperature (overnight and during travel) is another factor that should be investigated when trying to account for lower MPG. fimichael reports a drop of 2 L/100 km since temperatures have dropped below freezing.

I no longer have an 8, I returned it in September because of fuel consumption issues not because of lower HP. If Mazda can promise 12L/100 km hwy and around 10.5 city, I'll get another one. BTW it's not the cost that I mind, it's the fact that at 15L/100 km this car is less efficient than many SUV's.

Racer X-8

So, buy an SUV. Since when was the 8 supposed to be an economy car anyway? I suppose an SUV with a lame power plant (typical, but there are exceptions) would have better mpg. Go for it!

Your short repeated highway useage is exactly the clouding of the issue that I was refering to. The pitfall of statistical analyses.

mac

The question that I was asking, is it the short runs or cold temps or both. It would appear to be combination of the factors but the stats may show us that temp has more to do with it then distance. My current car (Integra) shows only a moderate difference in fuel consumption when doing the short stints and driving to Toronto and back (9.8L/100km vs 10.8L/km) while I see a drop of >1.5L/100km between summer and winter. The rotary may or may not follow this pattern.

Well, since you asked Mazda says 9.2 L/100 km highway and 12.8 city. I never expected an econocar but 15L/100 km highway!!! My neighbours Pathfinder v6 4x4 is no beast but is no slouch either and gets better numbers. The best I've seen posted here is 10.5 highway but most are in the teens with some poor sod getting high teens. And yes it is possible to get decent fuel efficiency with a high reving, nimble sports car, ie S2k. The 8 is still the car that I want most but we all have to decide for ourselves what is acceptable. All I said was if Mazda can give me 12 hwy, I will take it, but 15 I will wait for something else. I was hoping that this thread was going bring a solution to my dilema but alas it looks like I will have to wait a little longer.

8_wannabe

At least it brings an answer to your dilemma, but alas not the answer you were hoping for.

MPG > HP

Someone (CZ?) posted that the stock ECU leans out in the 4k rpm region, so a remapped ECU wouldn't help MPG much unless retuned for lower than 4k rpms. So, where next for improved MPG? CAI? Larger rear tire radius? Higher differential ratio? Catbacks? Which ones? How?

93rdcurrent

As far as SUV's go I can say that the H2 I test drove for 2 days was ranging about 13.5 mpg with 850 miles on it. My RX-8 with 1,800 miles on it is still only getting 14-15.5 mpg. Both were driven in same conditions and terrain. So Racer X-8 are you suggesting that we should expect to have our cars pelted with rocks and acid by enviromentalists any time soon? And as a side note the mpg were not listed on the H2 because of its' weight class. I know that I am not competing with the H2 in its' weight class but it seems that I am in fuel consumption. Apparently the EPA standards were done for a car not driven in typical city driving conditions becuase, as I've read on the forum, most of the people posting about fuel economy are driving a good portion of the time in the city and not on the highway. I didn't tell Mazda what to post for mpg they did that all on their own. I just want them to live up to the standard they already set. Let me know if that is so wrong.

SecrtSqurl

On a daily basis I do not have to get on the freeway to drive. I do drive roughly 45 mins to work. My car has always gotten 175 to 180 miles before te idiot light comes on. Roughly 14 mpg. It has never changed. Today I went roughly 276 mile before it came on. That is 14 city, 21 hwy. The suprising thing was that on the hwy i was never under 70, and was mostly over 90. The gas mileage sucks, but I was suprised at todays hwy mpg.

DrDiaboloco

Holy resurrected threads, Batman!

The only thing surprising about your newly-achieved highway mileage is that it was as HIGH as it was, since you claim to be driving around at 90+.

SecrtSqurl

It suprised me also! The car just seems to like to go fast.

Winfree

I wonder what kind of cars and what kind of milage executives and CEO or the 8 big oil companies are getting? Any known stats?

bigguy

Just a thought... My LR3 landrover weighs almost three tons with me driving and my RX-8 about 55% of that. The rover gets 14mpg and the Mazda 17mpg. Some how I seem happier with the LR3's milleage... though both are at about the EPA city range. On the highway the rover gets 17.5 (close to it's 18mpg rating, the Mazda get's 21-22 hwy - 3mpg short of its hwy rating. - I bet if sixth gear was just a little taller the MPG in real life would match the current EPA numbers. I'd like to turn 3000 RPM at 75MPH - not 3750.

I'm not really that upset about the milleage on the eight either. For the money I saved vs. other cars the effective miles per gallon is more like 22-28 mpg city instead of 17.

MikeTyson8MyKids

iTrader: (1)

I get 22-24 on the highway with air running. Not sure about it off, its been blazing hot here.

DrDiaboloco

Same here... Hot, that is. I beat the Monroney sticker in cooler months with no AC (I don't have the numbers in front of me, but I think my high was 25.5MPG, but even that used a LITTLE bit of AC for demisting) and now I'm right at the rated MPG, at least on the highway, even with the AC on. Ranges from 23.5-24.8. That high tank actually pushed me over 400mi on one tank, which is about as good as I'd ever expect from this car. Just slightly less range on one tank than my Mazda6S 5spd achieved on ITS high tank, but of course that car had a smaller tank.

For the record I do 72-77mph, depending upon the posted limit... I've got more to lose than just some points on my license and higher insurance if I get speeding tickets.

misterius

My MPG is nowhere near the numbers bandied about here. I get about 16 mpg with about 80% rural driving. I haven't been driving the car hard either because I'm still in the break-in period. A/C is blasting all the time, though, because I can't stand the California heat.

I hear a lot that the MPG improves with time. I'll be tracking my usage the next few months.