Hi all

I have been thinking about the fuel economy in light of the nature of the car, and I found something that while not new, is interesting comparison-wise. While it may be obvious to many, there may be those that wouldn't have considered this.

**so before I get flamed, I'm only trying to help **

One large complaint with the Rx8 is the lack of torque. This is very misguided. Torque alone has no meaning, until you consider the gearing. It is the wheel-torque that is effectuated that counts, and to this end knowing the nature of the rotary engine, Mazda created very aggressive gearing for the Rx8. So there is ample effective-torque if you drive it the way it is intended. But there-in lies the dilemma...the more you lead foot, the more it chews fuel.

Sooooo, investigating the gearing for the Rx8, I learnt quickly that comparatively its 1st and 2nd are signiificantly higher than say other sports cars. The Rx8 does however share very close gearing to the 350Z...and this point is important: The 350Z has a lot of low down torque, so it does not need to be revved as highly as the Rx8. We have the disadvantage, fuel-wise, of chewing disproportionately higher fuel in the upper rev ranges, but particularly in 1st and 2nd!!!! This is the major finding.

I think it would be fascinating measuring your fuel economy compared to your normal driving if you change gears in 1st and 2nd at less than 4000 rpm and resume normal driving after this. ie rev highly in later gears. I'm not telling people how they should drive, I'm just saying **IF**your fuel economy bothers you AND you would like to minimise it, maybe give this ago. If you try it, please post your pre and post MPGs and let's see some results. I'll happily tabulate them being the statistician that I am.



RX8 Type R 350Z S2000

3.760 3.266 3.794 3.13
2.269 2.13 2.324 2.045
1.645 1.517 1.624 1.481
1.187 1.212 1.271 1.161
1.000 0.972 1 0.942
0.084 0.78 0.794 0.763

 

Interesting. Sixth is defintely not anywhere near tall enough of a gear on the 8 to achieve S2000 or 350Z gas mileage numbers on the highway. A seven speed box where at 85 mph would put you around 3300 RPMs would work great for many. I'd be willing to bet that 30 mpg would remain a pipedream even if they implemented different ratios/extra gear.

{10 minute wait just to post. What's with all the "server too busy" B.S.}

 

3750rpm

 

Sure, I was just approximating. Actually seeing 3750 while driving is a tad difficult.

 

I would like to see to see a taller 6TH gear so 80MPH was about 3000-3500 rpm not 4K RPM, but even if we had a taller gear I dought we would get more then a 1-2 MPG improvement. I say this because I do a lot of freeway driving and I have used a whole tank of gas at 80 MPH (4K RPM) and only got 20 MPG and then I tried 65MPH 3250 RPM and only saw 21.5 MPG. I was at a much lower RPM and a lower speed which means less aero drag and still only 1.5 MPG better. Even with not MPG improvement a taller 6th would be nice.

I did not buy a RX8 for MPG, I bought it for the pure fun of driving it through the turns.

 

Even though I bought the car to burn gasoline, I too share the dream and yearning for money in my pockets. I drive and try to shift most of the time before 4k in 1st and 2nd (unless its time for the redline a day) just because I'm halfway to work before my car warms up and I'm always in traffic. anyway, I've driven a tank in all traffic like I stole it and like it was my baby, the difference was 16.8 on average for the babied tank, and 14.9 for the stole it tank. All that means to me is that I'm not going slow if I can help it.

 

As far as I understand, the designers of the car have a choice to make. Providing high torque at lower RPMs or providing higher torque at higher RPMs.

Advantage of Higher torque at lower RPM's may be fuel economy.
Advantage of Providing Higher torque at Higher RPM's is speed and Power. But we know that Higher RPMs is lower mileage.

This link may be of interest to some of you.
http://vettenet.org/torquehp.html

 

shifting that early would defeat the purpose of the car. Face it, the car isn't great on MPG. Drive it! Enjoy it!

 

I find that I usually shift before 4k when there are a lot of cars around. There's no need to wait to shift when you'll just be holding that RPM (above 4K) constant cuz the traffic ahead of you isn't accelerating as quickly.

 

3750 is easy to find. when your rpm needle hits the tick between 3500 and 4k, SHIFT. 3750 is where the next path of the intake manifold opens for the secondary ports. avoid that and you save gas. also shifting that early doesnt "defeat the purpose of the car" i actually shift at 3-3500 quite often along with my frequent trips to over the stock redline. if there is a line of 4 cars ahead of me on the 1 lane(in each direction) between me and the highway with with double yellows and 30-40mph speed limits there is really no reason to rev much higher- all your doing is making more noise. whats the point of running around at 30mph at 7000rpm when you simply will have to stop with all the other cars at the next light?

i can follow those other cars at 30-35 in 4th or 5th gear and simply enjoy playing with the apex of the curves as i drive along. often i need to shift back down to avoid bogging the engine because the other cars simply cant maintain the speed through the curves like the rx8 can. when i get to the 2 lane(in each direction plus a turning lane) that dumps me onto the highway i can downshift drop the hammer to move a round a couple cars and hit the on ramp hitting the redline in 1,2 and possibly third(depending on traffic, weather etc).

but when im in a chain of cars i just dont see the point of staying much over 3krpm when i can just down shift when i get loose.

 

Thats a very interesting insight zoom44. Are you saying that you make a shift before 3750 rpm to save on gas?

 

Very interesting, but you left out an important factor; the rear axle gear ratio. The RX-8 has a 4.44 rear axle and the Z has a 3.54 rear axle ratio.

1.3L

 

The best way to get best MPG for me is,,,,don't use 10% ethanol.
plus premix 5 ounce per tank.
73 highway speed helps.

 

i usually shift at about 3000 during inner city driving. 4000 if im feeling sporty.

 

Who spends any time driving around in 1st and 2nd ? 99.9 % of your driving is in higher gears . Your reasoning is not logical .
However if you were to say - don't redline it through the gears every time you accelerate that's different but also very obvious that not doing that would save gas.

 

Just like zoom44 said, I always (when just cruising at least) shift before the secondary ports open at 3750 rpm to save fuel (in all gears, not just 1st and 2nd). Seems to work for me, every tank since I bought the car 4 months ago has averaged between 21 and 23 mpg (60/40 hwy/city). I still have fun with it, redlining here and there, but when I'm just driving for transportation and not for entertainment, it only makes sense to drive economically. It's not hard, and the results are there.

 

Saying you spend 99.9% of your time in other gears while driving in the city is simply ridiculous. With start/stop at street lights and bumper to bumper traffic you will spend more time in 1st and 2nd than you care too. That was the whole point of my post. I am trying to offer help to those in city driving. You will actually spend disproportionately more time in those gears than you would on the highway. So what I'm saying is without thinking and driving normally you will use more fuel in the rev-band 4000-9000rpm in 1st and 2nd. And you will be doing this a lot with stop/start driving.

 

I agree completely with zoom. Whats the point of making noise? But when I do go for speed I put it all the way up to the redline.

 

Probably a stupid question - how much does throttle position play into this? How does WOT at low RPM compare to 50% throttle at higher RPM?

 

^I've been curious about that too...

 

when my car is parked during the winter, I get GREAT MPG

 

Sorry but 0/0 is undefined...it's not infinity

 

I ride my Camel to work.

It saves on the RX fuel milage.

A tank of gas can last me 4 months!

I think Deedub gets better milage than this!

 

All we have in Chicago is 10% ethanol but if you do the math your only looking at a about a 3% reduction in mileage with this mix. Thats about the differance of getting 19.4mpg as opposed to 20mpg.

 

Maybe..