How do we improve the mileage on our cars? A brainstorming session
 

How do we improve the mileage on our cars?

First off, what we have is an engine that has great power to weight, but poor fuel efficiency to power. That’s what we have, so we can’t do a whole lot about it. But, it got me to thinking, what can we do otherwise to help out at the gas pump (and, even more important for me, increase the range!).

What makes a car more fuel efficient? Better efficiency…in all aspects.

So, as I see it, there are a number of things that can be done.

Improve aerodynamics
What potential aerodynamic fixes would improve highway gas mileage? Would a flat bottom help? What would it take to do this? Plastic? Aluminum? What could be potential problems? Heat? How about the front end? Any improvements in managing the air?

Improve drivetrain efficiency
Given our RWD setup, what can be done? Would new fluids in the transmission help? And in the diff? Would there be worries about a lighter fluid contributing to increased wear? The engine already takes pretty light oil, so I don’t think there is much there. How about parasitic losses on the engine? We’ve got an electric pump for the power steering, but what about the alternator and air conditioner? Are there more efficient units out there?

Lose weight
In stop and go traffic, having to move and stop and move and stop 3000 pounds hurts the mileage. Trimming weight helps, but Mazda already has done a pretty good job at minimizing weight. However, we can still get lighter wheels, lighter tires, and a lighter flywheel. Speaking of wheels/tires, would a narrower tire help with aerodynamics? I’m not sure if I’m willing to give up on grip, but I’m just brainstorming here.

Change drivetrain gear ratios
I think having a taller 6th would help out. In my normal, sea level driving, there’s more power than I need in 6th. I’d rather it be a super tall mileage gear (like in a Corvette or Viper). I can always shift when I need to pass or hit a steep hill. Actually, combine the taller 6th gear with a little bit shorter differential ratio, and we’d have better acceleration and better fuel mileage.

Other?
Anyone else have ideas? Since Racing Beat really wasn’t able to get better fuel efficiency after cracking the computer, managing the air:fuel ratio apparently isn’t the answer.

Wild dreams?
What does a rotary do very well? Produce heat! Combine the heat of the rotary with the steam powered BMW turbo system and you’d be able to see pretty good gains in power and efficiency. Wouldn’t that be nice? Or add an electric motor flywheel like Honda has (though the weight penalty for the battery pack would be a bummer). Or…what?

Links
BMW turbosteamer
Weight of stock RX-8 parts

~ Matt

The problem is that no matter what you do you will end up spending more money in trying to maximize gas mileage than what you would spend in just paying for gas.

Well, this isn't really about money. It's more about what solutions can be found, and where the future of rotary engines can go.

Also, the range of the car (meaning frequent fill ups) is aggravating to me. I'm not sure what price I'd put on that.

a larger gas tank would be nice, it won't improve mileage plus it'll add weight, but will increase the length of your drive.

How about a sail to take advantage of the prevailing winds?

^ :cwm27:

Seriously though, the Turbosteamer concept is awesome! Designing aerodynamic fins for the reverse radiator would be pretty important though to prevent backpressure.

Pretty much everything you've said so far is true and will help, but costs a lot. I'm not sure there is anything so cheap that it pays for itself. Making more power-take off stuff like AC more efficient or electric is intriguing.....

stop shifting at 9k...but its too much fun to stop!

This one always works.

Between fill ups put in $10.00 worth of gas but don't count it when you fill up. The mileage improves dramatically and it doesn't cost as much as many mods :yelrotflm


Okay that was silly.


This one really works.

Just make sure that all your trips are long and that you don't sit in traffic. This mod costs nothing and improve driving enjoyment.



Okay, not very practical.



These will work...

Get a ride with someone else.
Buy a fuel efficient car.
Move closer to work.

Pay for your gas by swiping a credit card and do not look at the pump. Have your wife do the bills so you don't have to look at the statement too. Does wonders for your worries ;)

This is the best solution for your primary concern, range.

I could stand to lose 20 pounds and get back down to my fighting weight. I'm sure that would help!

I got 19mpg on a 278 mile round trip last weekend (I thought I was riding on fumes when I got home to the gas station right up the road but the car only took 14.5 gallons on fill-up so there was still over a gallon left in the tank). It really sucks when I used to be able to do the same trip in my Maxima in 1/2 a tank.

I try to limit the amount fo weight I carry but to be honest I noticed that last weekend when I made the trip (just me and my 90lb son and one small duffle bag) I got almost the same exact mileage as when the whole family goes (120lb wife and 40lb daughter plus shitload of clothes that comes with them). So you would have to lose a crap load of weight to make a difference. I also just got wider tires and it did not seem to hurt my mileage a bit. I did cruise at about 85-90 the whole way so I am sure cruising at 70 would probably have gotten me better mileage but I am too impatient.

I wonder how much difference smoothing out the bottom would help for the lower cars. I will be swapping tranny and diff fluids at the next meet so the next time I go up to my pops house I will see if that makes a difference in mileage. I have also just upped my tire PSI to 34 so maybe the combination of things will increase it a bit.

Simple solutions. Sad but true.
:)

a piggyback retune will actually give you better mpg if you regularly 'drive it like you stole it'. Does nothing for cruising so i don't cruise a lot :)

I've always been curious about managing the air under a car and how much it could help. Ferrari does it, so there must be a performance advantage. Is it so that they car run a diffuser, gain downforce, and not have a spoiler or do they do it to reduce drag to improve top speed? I'd like to think it is for both.

Oh, and yes, I know to improve my mileage/range, I could buy a different car, or drive it like an old lady, but really, I think this goes beyond the current RX-8. If you had a clean sheet design opportunity for a car with the Renesis engine, how could you make it reasonably fuel efficient? Given where the cost of gas is and the mood of the world, it's going to have to be somewhat efficient to sell. If we could actually to 18/24 city/freeway regularly, I'd be happy. What can be done to the rest of the car to get there?

I've been wanting to see someone take the first-gen rx7 and stick a renesis in there. That body was wicked light...

If Mazda's engineers couldn't get better mileage (and that's knowing critics would be waiting, armed and loaded, to attack the new RX car's fuel economy), I have this crazy feeling we're not about to figure it out here.

:)

I thought that more weight actually helped gas mileage on the freeway (or whenever you're maintaining constant speed) because the increased momentum helps to carry the car. Not sure if this is correct.

Reprogram the fuel system to deliver a leaner mixture. AKA better fuel map.

Leaner mixture equals burnt out cat. I have never had a problem with fuel economy. I get 28mpg on cruise and 23mpg around town. Always warm up the car, and drive teh car wtih the traffic flow. Don't always rev to 9k but usually 4-5k between shifts. Get into 6th gear as soon as possible.

This always surprises me. Most all of us get mileage in the high teens, but there are a few people out there that get significantly better mileage. What's your cruising speed? I've done pretty much entire tanks of gas on cruise control on the freeways and I'm lucky to break 20 mpg. I usually set the cruise at 74 to 76 mph.


Racing Beat has tried and they haven't had much luck. Check out this link.

I recently moved to CA from Georgia and have noticed a 1-2 point drop in mpg. I've tried to bring up my mpg, back to ~20, but to no avail. I have a feeling it's the hills here in CA. So, I believe CA should repave all their roads to be the same elevation.

Just kidding.

FS

I get about 18-21 here in Middle Tennesse. Plenty of hills here to. I'm afraid it the gas in CA. Does all the Gas in CA have ethanol? All cars get worse gas mileage with that stuff.

I cruise at 70mph. I use Mazda Rotary Oil in the motor and use 95 octane (Aus). This I think is equivalent to 93 in the USA. Drive it hard for fun at times but usually have a gentle R foot. I find that the heavier your R foot, the worse the fuel economy.

Yea, I just read about this stuff:

California was one of the first States to ban the gasoline additive methyl tertiary butyl ether (MTBE) after it was detected in ground water. Ethanol, a non-petroleum product usually made from corn, is being used in place of MTBE. Gasoline without MTBE is more expensive to produce and requires refineries to change the way they produce and distribute gasoline. Some supply dislocations and price surges occurred in the summer of 2003 as the State moved away from MTBE. Similar problems have also occurred in past fuel transitions.

Plus, our special blend isn't supplied by many companies.

FS

Does Australia use Imperial Gallons? That is different by a fraction that would make sense of 28 mp(I)g.

There's a few things I'd like to see done that would improve economy and all around performance. Unfortunately to do them would mean you no longer would have an RX-8. Maybe for another car though such as one based on the Kabura.

I'd like to see a car weigh no more than 2500 lbs max fully fueled. The lighter the better.

Better aerodynamics with careful underbody attention as has been mentioned. A lower drag coefficient helps at highways speeds.

I want Mazda to dump the damn 4.44:1 rear end ratio for something more real world. It's way too high. At the very least take it back to a 4.10:1 which is more than enough.

A smaller turbocharged rotary such as a 1 rotor turbo Renesis that puts out 200 hp. In a 2500 lb car it would be a lot of fun. This setup would also be more fuel efficient.

Those are a few things on my wish list. They should easily make for a car that car keep up if not beat an RX-8 in terms of acceleration and potentially handling depending on the car design. It should also yield a consistent 20+ mpg city and 30+ mpg highway. That's how I'd do it. Sorry guys. It won't happen on an RX-8. The first gen RX-7 idea is a good one though. I've got one. It's already under my target weight and already has a 4.10 rear end in it. Now if I could just afford a Renesis...

^ I'm wondering how much a 4.10 ratio would affect acceleration?

and as flexible as a rubber band.



But back on Topic... why would we even bother to look for better mileage???

what is wrong with the mileage of the RX-8? I typically get just a hair under 18 in mixed driving.

What is wrong with that??? That is the nearly the same or better than any other 200+ Hp modern sports car out there.

My 07 328i gets the same gas mileage with its 230hp motor. Yep, state of the art BMW motor gets the same mileage as the State of the art rotary motor in my 06 RX-8.

Heck, at least the mileage is better than my X5 which only gets 13 city and 20 highway.

I do have a suggestion that could work without spending any money .

I note with interest that some people get quite good freeway cruising MPG while most are 20 or below . Rather than blame the car , I would lay odds that those who get good mileage have have a slightly different driving style and here is why it makes such a big difference .
When you go from closed to open loop on the ECU the fuel consumption increases considerably .
The trick is to drive in such a way that you stay in closed loop as much as possible.

How do you do that ?
When you are at around 3700 rpm in 6th any slight acceleration will take you into open loop . The trick is smooth driving & no speeding up and slowing down at freeway cruising speeds .
For me this is impossible because this is boring but for many of you it would not take much of a change in driving habits to improve mileage .

trade it in for a Honduh ...

IMO, I think that the 6th gear is about as tall as it should be. With the low amounts of torque, I would think that making 6th any taller would bog the engine down terribly. It already has minimal pull in 6th.

I understand the thought process behind it, and as nice as it would be, I think that it's just not practical with a Renesis. I too thought it sat a little high in the RPMs when cruising at 70, but if hooked up with a taller gear, it would be about equivalent to mashing the gas in 6th going 45. Except you would be going 70...and likely would need the speed a little quicker.

Hydrogen Electrolysis
 

www.savefuel.ca
Too lengthy to explain here, but I have one of these units currently and I am getting twenty four miles to the gallon. And actually anyone can make one of these (high school science class, anyone? anyone?). All that you're basically doing is breaking water down into its elemental components (hydrogen/oxygen) and burning the hydrogen with the air and fuel instead of just burning the air and the fuel. All that I can say is..It works and pays for itself in about a year.
Otherwise, here are some options:
http://waterpoweredcar.com/hydrobooster2.html
http://www.thesietch.org/projects/Hy...aker/index.htm

hmmmmmmm

What type of snake was this oil extracted from?

AT 12 mpg, I'M LOOKING!

The 8 gets inconsistent mpg among its owners...some, like Raptor, gets horrendous mpgs, while others get 20+. Myself, I noticed that between city and highway, there isn't much change: 19-20 mpg. As for the driving style, I recently added some Chevron Fuel Injector cleaner with the V-power from Shell and am redlining it 2 times/day on a consistent basis and am noticing that the mpg isn't affected yet (150 miles at slightly under half-a-tank): carb-cleaning run @10K. I'm assuming when I fill up that my mpg is @17 or so. Not that much, considering I've been redlining it twice/day....wish my highway miles were better...but since I get such good in city mpg, I'm not complaining :) Just noting that mine is different from others out there...

I always figured that with the handbuilt Renesis engine, there must be some variables from engine to engine and that those that were getting better mileage must have a leaner air:fuel ratio helping them out (maybe differences in the MAF). But, when Racing Beat couldn't improve the mileage with a cracked computer, it really became a mystery to me how some people get such good mileage. I mean, if I drive on the freeway using cruise control, shouldn't I be able to match the high mileage some people get? There's something not connecting, but I don't know what it is.

Yep. Don't understand either..when I'm on the highway and set it to cruise, I don't seem to be getting as good as other 8 owners who says they had up to 25 mpg...I be lucky to break 21..but..like I said earlier, at least I'm getting somewhat decent mpg on both city & highway drives..when my mpg drops drastically..that is when I'll check out the MAF, air filter, plugs, etc...

I know it's not an RX-8 but my Honda has the same issues with cruise control. I can get better freeway mileage without it. This is due to hills and overpasses. Unless you are a completely flat road for miles on end, you should be able to beat the cruise control. When going up hills, even small ones like an overpass, the cruise control gives it more gas to hold the same speed. On larger hills (and I'm not talking about mountains) it may even floor it. I on the other hand may just let speed fall off a few mph or so. This actually saves alot of gas and your drive time doesn't suffer appreciably for it.

RG..does this applies to manual as well? I know this applies to automatic, since the computer isn't smart enough to know what gear to put itself in for the best performance (usually, it just floors it vs. gradual gas increase)...I'll have to drive it next time without cruise to see if it makes any difference..not that I'm complaining..but..it is weird..

I am a big cruise control user and I average only 19MPG on long road trips and there are not many big hills on the highways I frequent.

I've never owned an automatic.

Interesting take. I EXPECT my cruise to hold the speed I set it at. The 8 has been my best cruise control yet. Mainly because I set my cruise at the speed where I hope I won't get a ticket.......

When driving manually I don't let speed drop on purpose, however it probably does. On the same note, it climbs much higher when on manual as well....

I think a possible answer to better milage, at least on the freeways, would be some sort of rotor deactivation system (like Dodge has on their Hemi's).

We could program the ECU to run on one of the rotors while on the freeway just cruising and have both rotors kick in when we punch the gas or for normal driving (Manual override should be available of course :) ).

Either that or just have the motor alternate every other combustion cycle to deliver a charge. I like this idea best so it doesn't upset the balance of heat in the ngine too much or cause uneven wear.

Sounds simple enough........right? :Freak_ani


:dunno:

The only way to get it to alternate every other combustion cycle would call for a serious fuel delivery system redesign. It would have to include a direct chamber injection system due to the length of the runners and the number of intake ports.

Has anyone had any success running standalones on a Renesis yet?

hey, rotor deactivation. Great idea if it could be done.

I'm using four of these in my RX-8, and I've been running on the same gallon of gas for 2 years. Plus I use the surplus Hydrogen to heat my house. :lol:

I played with deactivating one rotor on my RX-7. I had to floor it to hold abour 45-50 mph in 1 rotor mode. It was quite lethargic and vibrated very badly. Admittedly it probably wasn't anywhere near an optimal setup but the first results weren't too promising. I'm sure it could have been improved upon in some way.

Well if Mazda is working on Direct Injection for the Renesis, then we just might have a solution. That way we can run both rotors and just alternate every other combustion cycle and not have the vibration associated with rotor deactivation that RotaryGod experienced with his experiment. :)

Your best bet to max mileage for minimum cost would be too:

1. Properly inflate tires
2. switch to synthetic tranny and diff fluid / synthetic motor oil
3. frequent clean MAF and filter
4. Racing Beat Intake system
5. Use 6th gear when ever possible

doing the above I average about 16.5mpg city and 24 / 25 HWY