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.

 

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.

 

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: 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.

 

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!!" )

 

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: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..."

 

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



...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.

 

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:

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

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.

 

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.

 

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?

 

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".