wingman_x

I know there are lots of postings about fuel economy, etc, and to those that feel I should have put this there I'm sorry. But it's not often that an RX-8 hits over 500KM on a single tank, so I thought I'd share it with others.

This was on a trip down the 401 from Toronto, ont, to Ottawa, ont. If the last 50km wasn't city driving, it might have even stretched to 550 or even 575km.

The key was that the speed was 110km/hr (slow by my taste, but I had to see if I could break 500 =)

Attached is a photo with the proof (yes the low fuel LED is lit, and yes the trip meter was reset at the last fillup), as well as other progressive points (300/400km & fuel reading).

It can be done! it's just not as much fun as burning off 300km/tank

Rems31

My friends and I also drove from Toronto (Mississauga) to Ottawa this weekend. We took my friend's 98 Camry. We made it there in a little more than half a tank going roughly 120 kph.

Jethro Tull

iTrader: (6)

Keeping the RPM's down is the key to better fuel ecconomy. It's intuitively easy to see that you will be burning AT LEAST twice the fuel at 6K rpm than you do at 3K rpm because of twice as many combustion cycles per unit of time. More, actually, but this aspect is easily visualized without getting into other nuances.

But as you pointed out, wingman, it's not as much fun being ecconomical in this car as it is putting your foot down!

It might be interesting to see what the absolute best fuel ecconomy possible is with an RX-8. How far can one go on a single tank if using all the tricks?

BTW, do you Canadians use the term "mileage"?

Rems31

yea we use mileage...kilometerage just sounds weird

nate340

I’m impressed, I usually get around 380-460km a tank. I get to go on a 16hour road trip later this month ill see if I can break in to the 500’s

boffam

iTrader: (1)

Musta been a stiff tailwind that day...

NgoRX8

iTrader: (1)

60-65 mph is the best range for good mileage highway driving.

i dont even care about gas anymore. lol

Jedi54

iTrader: (7)

I do 70-75 on the freeway and I can get 20-21 mpg doing that.
(assuming it's all freeway miles)

Mobile

I think "K" is usually the more acceptable standard.

ie. "What kind of k do you get out of a tank?"

Rems31

Well all of the people I talk to either use the term mileage or fuel economy. Or they just ask "how's this car on gas?" I use L/100km's though instead of mpg.

Razz1

I've gotten 22.5 MPG before!

dillsrotary

{does math} wow thats like 900 miles!

Jethro Tull

iTrader: (6)

^^no, 500k is 310 miles.

dillsrotary

^ i know it was a joke

Jethro Tull

iTrader: (6)

Thank god! I did a double-take and really DID do the math...

Jedi54

iTrader: (7)

I think the most I've ever pushed my car was around 250 miles; low fuel light turned on as I entered the gas station.

PerSmitt

Actually I believe that is very wrong. In an ideal world the gear would have no effect on the fuel economy at a certain speed. Simply for the reason that the force needed to drive the car forward is the same and therefore the same amount of energy is consumed and thus the same amount of fuel needs to be burned. Staying at a certain RPM cruising is less fuelconsuming than being at the same RPM during full acceleration. It has to do with the load on the car.

That said lets skip to a non ideal world. Yes higher RPMs will consume more fuel because of internal friction. Heat is generated and therefore energy is consumed. But that is definitly not the reason why the OP managed 500 KM. The key is air resistance. The force pushing your car back to slow down is the speed squared multiplied with a factor. Therefore the negative force is MUCH greater at say 140-150 km/h than at 110 km/h.

DMRH

My 03 model is a stock 4AT version with a recent KNIGHTSPORTS ECU re-flash.

Just found out the benifits of this reflash a few days ago.

900km trip from Sydney to Melbourne (land of Oz)

Cruised controlled @ 120km/h (3000rpm) with child & baggage for 1-week away.

Dead on 10km/lt highway travelling

Most economical rotary Mazda I have ever owned.

REgards

Jethro Tull

iTrader: (6)

Actually, PS, but my post is basically correct. Nobody disputes the effects of air resistance, but at typical driving speeds its usually not an issue. And without wind-tunnel results we really don't know how aerodynamic the RX-8 is. We don't know it's "sweet spot" as regards trade-off between fuel consumption and air resistance. Keep your speed at 110 km/hr. and go for as low an RPM as you can without lugging the engine, and your ecconomy will be better.

RPM's indicate engine speed, regardless of what gear the transmission is in. Fewer combustion cycles per unit of time means lower fuel consupmtion. Some of the nuances that affect the basic premise are things like accelleration. Faster accelleration requires more energy be spent to get the car to the desired speed in a shorter amount of time- more fuel used per unit of time means lower ecconomy. But for constant speed and a reasonable load, lower RPMs will always glean better fuel ecconomy. Rate of accelleration can have as big an effect on fuel ecconomy as engine speed if the driver has a lead foot and is fond of jack-rabbit starts.

You do generate more heat per cycle with a loaded engine (higher gear) than you do per cycle with an unloaded engine in a lower gear, but since there are more cycles per unit of time in the lower gear, the total heat prodution is roughly the same. You can factor heat generation right out and for all practical purposes, and ignore it. We're not talking about hauling a trailer here, just normal driving variations.

There is probably an ideal speed for the car as regards friction, not just internal friction, engine heat generation, but rolling friction as well. What tires you run and at what pressure will have a large effect on fuel consumption. Generally, the wider the tire, the greater the friction. The tires most of us run on this car are designed to aid handling and increase friction- that's a strike against fuel ecconomy right there.

At a given speed, you will always get better mileage at lower RPMs than higher- that's the whole concept behind overdrive- and it works. Obviously you can overload the engine by going too low, but we aren't talking about the very extremes of the envelope.

matis

https://www.rx8club.com/showpost.php...&postcount=616

Try beating 600 with one tank

DMRH

Damn, thats exceptional mileage. 630km is simply awesome but hard to achieve with an RX-8.

Why...??

The incentive is always there to go faster.

Just did 590km on a single tank return trip from MEL to SYD. Got 59lt back into it meaning 2lt to spare......

Sure was sweating those last few km until the service station appeared. Speed/rpm was again 120km/h @ 3000rpm

03 model, 4AT version

REgards

PerSmitt

I see your point and you might actually be right

I just need a bit more convincing. This is how I see it: We drive in a certain speed in a low gear. Flywheel is loaded with power so for every combustion cycle we only have to add a small amount of energy to the system to keep it going. If we drive in a higher gear in the same speed there is more power loss from wind and such between each cycle and therefore we must consume more fuel / cycle. Hence the fuel consumption would be the same between a low gear and a high gear.

This is all in an ideal world. The only reason why I would want to accept lower fuel consumption in the higher gear would be if we have linear (or even exponential) losses of power in the drive train from engine to the gearbox. If we add those constraints I will agree lower RPM gives better fuel consumption.

So do you agree with my reasoning so far? The reason I don't count losses after the gearbox is because we have a constant speed there so losses should be the same from gearbox to the wheels.

Okay, that makes sense. I guess I was thinking on when I was driving on a track day and oh the engine got warm. But obviously that was not the high RPM's but rather the constant acceleration. A point I believe we both agree upon.

Here I don't agree completely either. I have attached a diagram with the test results of this made by Rototest (i.e. its official and not just something I am sprouting). They are testing a Saab -98 2.0T in fifth gear. If we look at the average consumption we see the lowest is in 90 km/h. If we were to drive in 70km/h in 5th gear it would not be overloading the engine, and the wind resistance should be less. But still something causes the consumption to be less. But I suppose 90km/h in 5th could be the sweet spot in the Saab.

I am trying to learn more and to think a bit so if you see any flaws in my reasoning, please tell me.