Prod

This is for those of you who don't know how a 1.3L R2 get 18mpg.

I'm not a big pistonhead/rotorhead but I've looked at how the rotary engine works and how piston engines work. Please, correct me if I'm wrong. The reason the rotary doesn't get good gas mileage is because it fires 3 times per revolution of the rotor. However, for each revolution of the rotor, the output shaft makes 3 rotations. Whereas a piston engine fires once for every 2 revolutions of the crankshaft. A rotary engine has a 1:1 ratio of revolutions per combustion, a piston engine has 1:2. So in theory, a rotary will get half the mileage of a comparable piston engine.

RX-8 w/238hp 1.3L R2: ~18mpg
Toyota Echo w/108hp 1.5L 4: ~38mpg

Double the horsepower, half the mileage. Seems fair to me. Let's not forget that the Echo is meant to be an economy car. Compare the mileage to a 2.6L V6 instead of a 1.3L 4 and I think the numbers make a bit more sense. Once again, correct me if I'm wrong. I don't know that much about cars beyond what my friends have told me and what I've researched while car shopping. I am not a mechanic and I don't own an RX-8... yet. Let's hope that changes in a few months. I'm test driving one this weekend.

ptiemann

There is a very old post (maybe even dated 2002) by user rotarygod who explained in great detail, why you could say the Renesis has

- 1.3l
- 2.6l
- 3.9l displacement.

Honestly, it was a bit over my horizon, I would have had to spend more time on it than I had that day.

I'll try locating it, however, as a summary I remember that you could consider the Renesis any of the 3 above.

On another note, a Corvette has 5.6l displacement and gets supposedly 29 mpg on the highway, so this little math of yours doesn't quite work.

My junker ('92 Festiva) has a Mazda 1.3l B series engine, gets 48 mpg on the highway. Hm, if we consider the Renesis to be 3.9 then it makes sense..

Mazda Renesis: 3.9l --> 16 mpg
Mazda B series: 1.3l (4 cyl) --> 48 mpg


:-)

I'm going to look for Rotarygod's posting now and will post the link here.

-Peter

ptiemann

rotarygod's posting:

https://www.rx8club.com/rx-8-discussion-3/new-renesis-utilizes-helmholtz-tuning-5710/

yipyip

I don't own an RX-8, but owned one of the early original RX-7s (1979 with an April '78 production date). Anyway, my mileage on that was 13-17 typically, and as high as mid-20's on long trips. Of course there are emmissions considerations here with the new engine, but I find it incredible if the RX-8 cannot deliver better than a 25 year old engine did.

Regardless, I was wondering if anyone has experience with the optional REAR WING improving mileage. Apparently the Euro version of the car has this, in order to meet stricter fuel economy standards. Check out the link below, and read the caption below the picture about inclusion of a "boot lip spoiler" to improve fuel economy.

http://www.mazdarx8.co.uk/upclose/ipix/exterior.asp

Also, check out the link to the Euro mileage ratings. They appear to be higher - up to 32 mpg in "extra urban" whatever that is. I realize testing standards there may differ and, not sure, but do they use Imperial gallons which differ from US gallons?

http://www.mazdarx8.co.uk/upclose/specs/specs2.asp

Regardless, does anyone have thoughts about the spoiler improving economy?

hotpot

Yep. In the UK they use Imperial gallons and therefore their stated mpg figure would be higher than in the US.

The mileage and emission issues are probably the reasons why other car companies have not developped rotary engines.

KKMmaniac

I think JaegerNH has a good point. I know my mileage has improved quite a bit from my typical winter mileage just by observing the gauge. I gave up keeping track of it this winter, it was so pathetic.

The fuel formulated for warm weather should help. I also noticed my oil coolers were barely warm to the touch after a long drive in cold weather; cold oil has gotta be a MPG killer. Now with ~9000 miles under the belt, it's gotta be much better. I'll find out how much better this weekend.

Incidentally, my RX7 probably gets better mileage than the 8, but sure doesn't go like the 8!

artmt

Noone here is talking about 28/30. That's a straw man. 18/24 is the figure that is being discussed.

I am curious how you would feel if your 8 was delivered with rear seats missing. After all it is a sports car and those who want to carry passengers should get a minivan. Right?

cruzdreamer

I get between 13-14.5 mpg, have an auto and do mostly city driving. I'd love it to be around 17mpg....I'd be happier. I have over 5200 miles on mine and just had the L flash done......car seems smoother and a little more powerful. I will watch closely when I fill up next and report any changes in gas mileage. I understand why people complain...it is a sports car but if they say it should get around 18-19mpg city then 17mpg should be obtained in the minimum. Don't get mad at people who are disappointed. This car is geared toward people like me too.... with the freestyle doors, sports car look and handling and is not about the speed! I hope Mazda has the message and can make improvements....I love this car...it's beautiful and i am still in awe!!

Katchoo

Auto: 20-21 MPH all the time...got 23 MPH the other day driving 70+ MPH for 400 miles. Not bad.

Wish I knew what 'flash' I had...darn.

f1michel

And i'm pretty sure you will never get it so buy a cobra !

Anubis Rising

I agree with ya, that was a stretch for the MPG, just a example. but on your
point, course I would be upset there wasnt any back seats
which is why the concept does work, sports car kid hauler.
And man, where in my post did i say that this wasn't a
sports car?

rotaryDemon

i'm still getting 12-15. loving every MPG of it. MUHAHAHA!!!

Raevik

I'm on a sad trend right now.

First tank on the engine was 18.9 mpg, then 18, then 17.5, then 15.6, then 14.9.

Currently at 1/4 tank with 165 miles on it, and that was with gentle driving and some highway miles too.

Sigh.