Vaillant

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

HeavyMetal699

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.

Vaillant

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.

dillsrotary

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.

otherside

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

flomulgator

^

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.....

ucleadguitar

iTrader: (1)

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

DarkBrew

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


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.

musclecarconvrt

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

spooledUP7

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

9krpmrx8

iTrader: (46)

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.

SOVINE

Simple solutions. Sad but true.

Brettus

iTrader: (2)

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

Vaillant

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?

CnnmnSchnpps

iTrader: (1)

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

New Yorker

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.

limpy81

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.

Raptor75

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

SymSym

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.

Vaillant

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.

fullsmoke

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

musclecarconvrt

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.

SymSym

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.

fullsmoke

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

flomulgator

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