I know this topic has been discussed in the past, but now that we have some hard numbers, (ok, so the official EPA figures still aren't out yet) mainly from Car and Driver, I want to hear how others feel about this topic.

I tend to forget where I heard what, but quotes similar to this one: "Also, it's more economical than the RX-7's 13B, getting up to 30 percent better fuel economy in certain driving situations." (Road & Track, April 2002) have been made in regards to the Renesis and RX-8. Well, the RX-7 (FD) 5-speed was EPA rated at 17 mpg city/25 mpg highway. Car and Driver, in their September 1993 test found the FD to average 14 mpg on a 1500 mile trip. In comparison, the RX-8 was EPA rated by C and D in this April's issue at 18/23, with 15 mpg being the average on a 500 mile trip. This doesn't look like a noticeable improvement to me.

I realize, if we're after performance, it is unlikely we are going to get economy-car gas mileage results. However, in the normal mid-rpm, ease down the throttle pedal, day-to-day commute, I was hoping the RX-8 would out-do my WRX in fuel mileage (20 or so mpg) by a tiny bit. I would also argue, the EPA numbers shouldn't be affected by the opening of the third port, as that occurs at a fairly high RPM range that probably wouldn't occur in regular (careful?) freeway driving.

Does anybody else think my gripe is at least somewhat legitimate?

I dunno... I saw the same thing and was concerned, but a *lot* of that mileage has to do with HOW they were driving the car.

I think that they were running typical 'track days' almost every day on the RX-8 and for the most of us, that won't be the case. I believe the stated figures so far are something like 21/24 or something like that... which isn't great by any stretch but not terrible either.

Time will tell.. I don't know about mileage yet.

Car and Driver typically flogs the hell out of their cars, so I wouldn't be too concerned about the reported mileage. IIRC, they got 12 mpg in the Mustang and 16mpg in the G35, so the RX-8 is right where it should be.

Originally posted by Hercules

Time will tell.. I don't know about mileage yet.

So do you know about the 'fun to drive' factor, the 'sufficient torque' and 'backseat practicality' yet? or are those also 'time will tell' things? ;)

My opinion: time has already told me having had earlier NA RX-7s that fun to drive will be just fine, thanks. And back seat should be great, unless somehow I get the job of transporting members of a basketball team, a lot. Torque isn't even an issue - if I needed torque I'd get a turbodiesel truck. Agree Herc??

Originally posted by KKMmaniac
Does anybody else think my gripe is at least somewhat legitimate?

Yep. I was expecting at least 20 mpg in the city and around 27-28 on the highway; I get 17/23mpg in my 86 GXL.

I'm not disappointed in the city mpg. I think if you drive for fuel economy (keeping the revs below 3500), then 20mpg shouldn't be out of reach.

However, the highway mpg bothers me simply because I think 6th is too short. Around 4,000 rpms for 80mph? 6th should've been a true overdrive. If I remember right from Buger's post, theoretical top speed comes in fifth gear, so 6th wouldn't even be used on the track.

Brian

Right now I have a '94 Integra gs-r and at 4000 in 5th I'm doing exactly 80. I love the gearing in my car

I mentioned it in the Canadian forum after detailed specs from Mazda were relased (http://www.rx8forum.com/showthread.php?s=&threadid=2659&perpage=15&pagenumber=2).

The RX-8 will do, in litres per 100km, 12.8/city and 9.2 highway. That results in approximately 18.5/25 US MPG (http://www.pege.org/fuel/convert.htm). Curious that the auto tranny does even better on the highway with 8.8l/100km.

Is 18/23 the official EPA rating, or the C&D estimated rating? I'd be really surprised if the highway rating of the RX-8 ends up being worse than the FD, especially since there's the extra tall 6th gear...

I don't know if any of the older wankel engines used exhaust gas recirculation, but with only side ports, there could be egr.

Originally posted by Skyline Maniac


So do you know about the 'fun to drive' factor, the 'sufficient torque' and 'backseat practicality' yet? or are those also 'time will tell' things? ;) As per the C&D article, I sure do.

If it gets worse gas mileage than my tribute, which I dont think it will, i'll laugh. My trib gets like 18 city 25 highway.

Originally posted by m477
Is 18/23 the official EPA rating, or the C&D estimated rating? I'd be really surprised if the highway rating of the RX-8 ends up being worse than the FD, especially since there's the extra tall 6th gear...
4000rpm at 80mph in 6th gear, if this will be the case is not very tall imo.. My car is at about 4200rpm at 140km/hr.. I would have thought with 6 gears the 8 would have a taller 6th..

irish car mag says it's just under 30mpg clicky-clicky (http://www.mazdarotaryclub.com/forums/forum-photos/rx-8_irish-car-mag_febmar2003/rx-8_irish-car_02.JPG)

Don't forget that the British (and I'm assuming Irish as well) have a different gallon than the ones here in the U.S.
1 British gallon = 1.201 US gallons
So the British (and Irish?) should have about a 20% better mpg rating...

wow, i've never read that article.

Favorite quote: "Imagine the angst the RX-8 will cause. An absolute peach of a sports car and innovative to the nth degree."

Originally posted by threeputtwash
Don't forget that the British (and I'm assuming Irish as well) have a different gallon than the ones here in the U.S.
1 British gallon = 1.201 US gallons
So the British (and Irish?) should have about a 20% better mpg rating...

i thought that might be the case:cool:here (http://www.mazdarotaryclub.com/forums/showthread.php?s=&threadid=553) is where the rest of the article can be found:D

I too was hoping to get at least 30 mpg on the highway ata steady 60 mph. This is not too much to ask for, especially after the revelation that the RX-8 gets up to 30% better fuel economy than the last RX-7 in certain driving situations.
What better condition than steady highway speed?

Originally posted by Donny Boy

What better condition than steady highway speed?

Exactly. At steady highway speed, all that the engine is doing is countering friction from the road and air. Hrm, why is it that I have an urge to draw a Free-Body Diagram?

I think I was brainwashed in engineering school

~Jim

For what it's worth, the MazdaUSA website now lists the EPA figures:

6 sp. manual -- 20.4 mpg City 30.2 mpg Highway

Auto -- 21.3 mpg City 31.6 mpg Highway

Certainly a lot better than what Car & Driver experienced. I'd guess if you have the capability to keep your foot off of the accelerator, you can get pretty decent gas mileage.

As if that'll ever happen... :))

Looks like Mazda has left no stone unturned- great looks, great performance, and excellent fuel economy!

That isn't exceptional fuel economy, it is okay. Honda Accord V6 automatic 21/30 on 87 aki fuel.
An you need 90 (R+M)/2 too for the renesis. I am still looking for 90 AKI mid-grade
http://www.rx8forum.com/showthread.php?s=&threadid=877

considering the level of performance from the engine, its intended use, and the fuel consumption numbers of the ol' 13B, these numbers are incredible.... although yes, you can find many an engine which can sip the fuel more effectively, even in a bigger car. *shrug* who cares?? as long as it delivers where it has to (which it does in spades), s'all good.

Compared to its intended competition (350z, G35, IS300- etc), the RX-8 delivers excellent fuel economy.

Yes, I do know about the mileage of the Accord V6, because that's the other car I'm considering. But I have not heard one owner who has achieved close to 30 mpg on the highway, 24-25 is more realistic. These are two different types of engines, and the Accord's gearing is ultra-low (6200 rp/m redline and 5500 rp/m for the 4 cylinder), which is one of the reasons for the high fuel economy, and comparing the Renesis to the Honda J30 is sorta like comparing a F-16 to a 747.

The Renesis is the engine that will make even the most ardent Mazda and rotary naysayers (like even me a few months ago) stand up and gasp in awe. Low emissions, the best fuel economy in its class, and decent power without a turbo.

Anyone willing to bet me that the RX-8 automatic will be faster in the 0-60 and slalom than the Accord V6 Coupe automatic??? :D

An you need 90 (R+M)/2 too for the renesis.
I don't doubt what you say, but isn't one of the great advantage of the rotary the fact that it isn't picky about it's fuel? I've heard of rotaries running on hydrogen and alcohol, so why does the Renesis need a specific fuel? Any ideas?

20.4 / 30.2 ?

Now, those are numbers I can work with! I can live with <20 mpg under hard acceleration, but it is looking like the high 20's should be attainable during ~70mph freeway cruising. Cool! Maybe it will better my WRX by a little.

The '03 accord redlines are 6800 for the V6 (thank you VTEC)
and 6400 for the I4.

A guy at work has a 2000 V6 accord and can achieve 30 mpg @ 70 mph, the new accord should be better.

I will take that bet on the 0-60 sprint, but the Rx-8 will out slalom the Accord anyday.

BMW 330i gets better fuel performance than the RX8, as does
Acura CL-S,and TL-S. The 3 cars have engines that are more than twice as large as RX8's displacement. Dare I say, the Renesis engine is not as fuel efficient as it should be. Or is the lower fuel mileage a trait of the rotary engine? Either way fuel efficiency is not one of the RX8's strong points.

No flames please. Facts are facts.

Originally posted by Spoonie
BMW 330i gets better fuel performance than the RX8, as does
Acura CL-S,and TL-S. The 3 cars have engines that are more than twice as large as RX8's displacement. Dare I say, the Renesis engine is not as fuel efficient as it should be. Or is the lower fuel mileage a trait of the rotary engine? Either way fuel efficiency is not one of the RX8's strong points.

No flames please. Facts are facts.

The 330Ci coupe has similar fuel performance according to BMW USA:
6-speed manual transmission
City 21 mpg , Highway 30 mpg.
Not better, the facts.
:cool:

Originally posted by Spoonie
BMW 330i gets better fuel performance than the RX8, as does
Acura CL-S,and TL-S. The 3 cars have engines that are more than twice as large as RX8's displacement. Dare I say, the Renesis engine is not as fuel efficient as it should be. Or is the lower fuel mileage a trait of the rotary engine? Either way fuel efficiency is not one of the RX8's strong points.

No flames please. Facts are facts.
This will be interesting. You state that "facts are facts", but you obviously don't know much about rotary engines - as even you indicated in your post. So, then where are you coming up with the facts?

I'm just going to sit back and watch this one...

Originally posted by jonalan

This will be interesting. You state that "facts are facts", but you obviously don't know much about rotary engines - as even you indicated in your post. So, then where are you coming up with the facts?

I'm just going to sit back and watch this one...

And the Acura CL-S: 6-Speed Manual: 19/28 mpg. You can sit back indeed!:p

Spoonie said: Dare I say, the Renesis engine is not as fuel efficient as it should be. Or is the lower fuel mileage a trait of the rotary engine? Either way fuel efficiency is not one of the RX8's strong points.

I think Spoonie has a point, guys. I don't think the Renesis, or any rotary (unless there is another breakthrough like the multiple side ports) is going to be terribly fuel efficient. You get those rotors spinning to high speed and they are going to need fuel... six charge's worth for every spin of the rotors, three per rotor per spin. Though the eccentric shaft spins at a higher speed, those spinning rotors are what make the power.

Likewise, the small displacement means that without forced induction, high torque, especially at low rpms, is not likely to be part of the rotary equation either.

Car and Driver's real-world results are telling, no matter how they drove the car- sorry. Numbers don't lie, and they have achieved much better numbers with heavier cars with bigger engines. So... who cares? There is no need to apologize for every pereceived shortcoming of the car, as some here are wont to do. It's a rotary and it is going to burn a bit more gas because of it. The breakthroughs in power without forced induction are good enough, we can't get TOO greedy! I had a 1st gen RX-7 that got 16mpg tops out of its 100hp/105 lb-ft of torque. They are thirsty. I was always suspicious of the fuel economy claims made for the Renesis, and while the real-world reports from board members aren't in yet, I strongly suspect we will be reporting around 16-17 mpg in daily driving.

You can archive this post and beat me over the head with it if I am wrong... :D

You may find it interesting that reciprocating piston engines would still be more fuel efficient than gas turbines in aircraft applications, even with the high tech, fuel efficient high bypass turbofans of today. For an example, though, let's try a turboprop. A Beech King Air uses an 850-shp PT6A-42s turbine. If you were to make an 850 hp recip engine, it would require less fuel to make the 850 hp turbine, but it would be much heavier, louder, less smooth, less reliable, and would require more maintenance than the turbine. The extra fuel it burns is worth the trade-off.

Sounds a lot like a rotary, doesn't it? :)

The rotary is what it is: a comapct, lightweight engine that produces high horsepower at high rpms, perfect for a specialized sports car. And not terribly fuel efficient, not yet!

I think Don is right in a sense, that the rotary will be less fuel efficient than its competition.

However, I feel it will still be competitive. Looking at the C&D numbers, after really working up the cars in their review, they managed 15mpg with the RX-8, and 16 with the G35C. I think this is rather telling of real-world situations in that the G35 will obviously get better gas mileage on a day to day commute, as will the RX-8.

So I think while the EPA numbers are off, they aren't terribly far off. There are certain standards to meet before you get those numbers granted to you.

Originally posted by Hercules
So I think while the EPA numbers are off, they aren't terribly far off. There are certain standards to meet before you get those numbers granted to you.

yeah, the EPA ratings are just a metric which allow a fairly unbiased and fair comparison of fuel consumption, even if it doesn't really reflect reality very well (as owners of sports cars often don't accelerate with the thought of fuel consumption in their minds so much as "DAMN THIS IS FUN!!" ;))

Originally posted by jonalan

but you obviously don't know much about rotary engines - as even you indicated in your post.


Where did I indicate that? I got my information from http://www.fueleconomy.gov. What's so hard to understand about Rotary engines? It's not rocket science. A 1.3liter normally aspirated engine, should not have less or the same fuel economy as a 3.2 liter engine. Your right, I guess I don't know much about rotaries.

Herculese said:Looking at the C&D numbers, after really working up the cars in their review, they managed 15mpg with the RX-8, and 16 with the G35C. I think this is rather telling of real-world situations in that the G35 will obviously get better gas mileage on a day to day commute, as will the RX-8.

I get 16mpg in my day-to-day driving of my G35 sedan. It's a sedan, it's an automatic, I live in an area that is almost hilly terrain, and truth to tell, I do not drive overly aggressively, so I do not know how ultimately the numbers do compare. However, it does correspond to EXACTLY what C&D got, so who knows, maybe there is some bizarre algorhythm at work here.

If things work out and I get an RX-8 too, I will be able to compare them back to back. But given the close correlation between my G35 and C&D's test, I would not be at all surprised if my RX-8 returned 15mpg.

And honestly, it's not at all that positive that the RX-8 got worse fuel economy than a car that not only has a bigger engine, but is much heavier to boot. No matter how hard they were driven, etc.

PS Any G35 owner I know will tell you the G35 is a gas hog! The saying goes, "with the G35's V6 engine, you get V8 power with V8 fuel economy..."

Originally posted by Spoonie
Your right, I guess I don't know much about rotaries.

yes, you're right, you don't know much about them.
a 1.3L displacement wankel has a capacity of 2.6L per revolution... this is one of the reasons that it's not as fuel efficient...

another would be that the shape of the combustion chamber is not a cylinder, and thus there is a lot more surface area, and "cool spots" throughout it, reducing its thermal efficiency... and, in the old engines, unburned HC's would gather on the face of the trailing apex seal as the rotor turned to cycle through the exhaustion phase, and would spit all this "wasted" fuel out the exhaust port...

one could even argue (resonably) that the wankel (obviously) hasn't seen the level of development that its piston powered contemporaries have, and is thus behind the game from the get go.

these aren't the only reasons, and i'm not smart enough to claim to know them all, or even understand them all did i know... but, there are reasons, and these are the kinds of tradoffs one makes when determining the fundamental principles their engine of choice will work on: there is never any perfect solution in engineering... well, okay, sometimes there is, but there are always tradeoffs to be made.

every rotorhead knows that their dear engine gets crap fuel economy, for whatever reason (like those listed above), but don't care, because... well, Don said it well :)

Quoted from: DonG35Miata
The rotary is what it is: a comapct, lightweight engine that produces high horsepower at high rpms, perfect for a specialized sports car. And not terribly fuel efficient, not yet!

...although i'd like to add that even my "fuel sipping" Toyota Echo with it's pretty good 1.6L 4boinger is EPA rated at not-too-much over 30mpg (like 32 or something... IIRC), so with a 250hp wankel-powered car getting 30mpg on the highway, well, i must say i'm not dissapointed.

Originally posted by Spoonie
A 1.3liter normally aspirated engine, should not have less or the same fuel economy as a 3.2 liter engine.But then a 1.3L engine doesn't normally make 250hp, does it? Compare it against engines with similar power output, not capacity.

Originally posted by eccles
But then a 1.3L engine doesn't normally make 250hp, does it? Compare it against engines with similar power output, not capacity.

I thought of that. I was going to mention that the performance of the RX-8 puts it in the same league as its competitors in regards to fuel mileage. Your point is well taken.

Wakeech said:

one could even argue (resonably) that the wankel (obviously) hasn't seen the level of development that its piston powered contemporaries have, and is thus behind the game from the get go.

I strongly believe this as well. For the past 25 years, only one automaker- Mazda, hardly a large manufacturer- has worked on the rotary. Meanwhile, boingers have had 25 years worth of development from the EVERYONE- M-B, BMW, GM, Toyota, Ford, Honda- well, you get the idea!

Still, the rotary's simplicity has to limit development somewhat. Other than porting, timing, intake and exhaust, what else is there?

I own two pairs of the original Ohm Walsh series of speakers. The advertising campaign was "the last loudspeaker" because it was thought to be the theoretical ultimate in design and future improvements would be in materials and construction. One cone reproduced the entire sound spectrum omnidirectionally with no crossovers. The original pure Walsh speaker designs, while producing absolutely phenomenal sound, required a lot of power (think poor fuel economy) and could be blown up if users were not careful to overstress them... much like rotaries! Ultimately, to make the product more affordable and reliable, a tweeter was added and the one-way Walsh became a two way speaker, which is still sold today.

You can see the original Ohm ad from 1973 HERE: The Last Loudspeaker ad (http://members.aol.com/walshdriver/lls.gif)

The reason for my digression? Some simple designs don't have a lot of room for improvement/changes, etc. I think Mazda's future improvements are likely to be less dramatic than the improvement brought by the MSP. I hope they prove me wrong...

has anyone ever thought of making variable ports on a rotary? Dunno what kind of benefits that would make but it seems like it could provide some type of benefit. Maybe make it perform like Honda's VTEC system. You could have it setup for good economy or good performance.

Originally posted by wakeech


yes, you're right, you don't know much about them.



Thanks. I know a little more now.

Actually the G35 got 18 MPG in C&D :)


Certainly, if you rev the car to 9000 RPM on every shift, you are going to get crappy fuel economy. Believe me, I'm sure C&D's testers weren't taking a leisurely drive during their trip!

S2000's have huge variances when driven to redline (i.e. at the track) and driven leisurely around town or on the highway. I guarentee you most people won't hit redline on every shift on the RX8 (well maybe it'll take a few months after break in!)! Shifting at low - mid RPMs should deliver test results not ridiculously different from whatever the EPA tests indicate.

Originally posted by chenpin
has anyone ever thought of making variable ports on a rotary? Dunno what kind of benefits that would make but it seems like it could provide some type of benefit. Maybe make it perform like Honda's VTEC system. You could have it setup for good economy or good performance.

they already have a primitive system like this: the "tertiary" (as i like to call them: aka. 5th+6th) ports have a rotational sleeve valve (which is a tube with a hole cut in the side to match up with the port, and turns on it's longitudinal axis to open and close) which delays port closing, and obviously gives much greater port area when open... they used to work in the old FC's from gas pressure actuation (which in the stock setup meant from exhaust backpressure... which, yup, means you have to come up with a different system when you switch to a low BP exhaust)... i'm guessing now that they're a computer controlled solenoid or something, and come on at whenever the computer knows they're needed...

but yeah chenpin, this is one area, especially on the exhaust side, where the rotary would benefit from further development... slightly and finely variable port timing technology would certainly help the already good volumetric efficiencies of the wankel.

Originally posted by wakeech


they already have a primitive system like this: the "tertiary" (as i like to call them: aka. 5th+6th) ports have a rotational sleeve valve (which is a tube with a hole cut in the side to match up with the port, and turns on it's longitudinal axis to open and close) which delays port closing, and obviously gives much greater port area when open... they used to work in the old FC's from gas pressure actuation (which in the stock setup meant from exhaust backpressure... which, yup, means you have to come up with a different system when you switch to a low BP exhaust)... i'm guessing now that they're a computer controlled solenoid or something, and come on at whenever the computer knows they're needed...

but yeah chenpin, this is one area, especially on the exhaust side, where the rotary would benefit from further development... slightly and finely variable port timing technology would certainly help the already good volumetric efficiencies of the wankel.

Very interesting. Thanks Wakeech! I thought of this when I was doing some reading on rotary porting. Seems to me that very dramatic ports like Bridge or J ports offer good power but Poor drivability, fuel consumption, not to mention short life span. It would be interesting to see some variable ports that can can dramtically change port size and shape giving u in effect, a virtual J port when ur really gunning the thing. Do you think it would be possible?

Car and Driver recently tested the RX8, and they observed a staggering worst-than-SUV fuel mileage of 15mpg. How can this new Renesis Rotary engine make this poor mileage?

Originally posted by melvincat03
Car and Driver recently tested the RX8, and they observed a staggering worst-than-SUV fuel mileage of 15mpg. How can this new Renesis Rotary engine make this poor mileage? By beating the crap out of it, and never letting off the gas. Just the way I expected them to test it :)

If you look at the G35 it got 16mpg and is rated much higher. It's rare to get that low unless you're really hammering the car which is obvious... they were :)

I think the RX-8 should see some very reasonable gas mileage for a car of its type.

Still, if that's the way they test cars, then the RX8's efficiency still falls behind the others. Don't forget, the RX8 uses Premium gas.

What's the EPA rating for the RX8? C&D printed 18 / 23, and Road and Track uses "est" ratings. Mazdausa website is "TBA".

Actually, Herc they got 18 MPG for the G35, but I agree with you there. :) Redlining on every shift will kill your gas mileage. Over the long-run, most drivers won't drive their car like C&D did(though a lot will have spurts where they do!).

The Mazda site now says 20/30, but I don't think its official yet.

[QUOTE]Originally posted by Hercules
By beating the crap out of it, and never letting off the gas. Just the way I expected them to test it :)

Isn't that the way they treat all the cars they test? And still several cars, that were tested using the same methods attained better MPG numbers. Okay, maybe they wouldn't treat a Honda CRV the same way they would a 330i. But the RX-8's MPG numbers can be used in comparison to the other performance cars that they tested because they drive the hell out of all the performance cars that comes into their (C&D) hands.

Originally posted by melvincat03
Car and Driver recently tested the RX8, and they observed a staggering worst-than-SUV fuel mileage of 15mpg. How can this new Renesis Rotary engine make this poor mileage?

Any kind of car can be used as an example. It all depends on how the car is driven. My integra GS-R has a range of 15-41mpg. I can easily achieve either rate by driving accordingly.

Originally posted by chenpin


Very interesting. Thanks Wakeech! I thought of this when I was doing some reading on rotary porting. Seems to me that very dramatic ports like Bridge or J ports offer good power but Poor drivability, fuel consumption, not to mention short life span. It would be interesting to see some variable ports that can can dramtically change port size and shape giving u in effect, a virtual J port when ur really gunning the thing. Do you think it would be possible?

:D me and Boogdawg were toying with the idea in my favourite thread of old "How the RENESIS Makes More Power"... :D

... also, i was thinking along the lines of having side port exhausts, and a perhipheral intake port which could be actuated via butterfly valve (or act as the main, with the side ports as the controllables...)?? :D

Originally posted by Spoonie
[QUOTE]Originally posted by Hercules
By beating the crap out of it, and never letting off the gas. Just the way I expected them to test it :)

Isn't that the way they treat all the cars they test? And still several cars, that were tested using the same methods attained better MPG numbers. Okay, maybe they wouldn't treat a Honda CRV the same way they would a 330i. But the RX-8's MPG numbers can be used in comparison to the other performance cars that they tested because they drive the hell out of all the performance cars that comes into their (C&D) hands.


Good point. They must have floored the cars all the time. But all 3 cars should have been driven the same ways. There aren't that many methods to test cars. 0-30, 0-60, 0-100, Emergency lane change, braking, lateral grip, etc. So if the RX8 got 15mpg with the same way the G35 got tested and got 18mpg, in real day driving, the G35 might be getting 20-23mpg, while the RX8 could only get 18-20mpg. Well! Don't know! RX8's fuel economy isn't that optimisstic.