graphicguy

I drive mine like I stole it....redline whenever I can. After starting out pretty dismal (about 14 MPG), I'm getting about 17-18 MPG in town and 22MPG-24 MPG all interstate (except when some "doofus" challenges me and I have to run up to 100 MPH +) with 3K+ miles on the odo.

Since winter has hit, those numbers have dropped again. I do believe it has more to do with "reformulated winter fuel" than anything else, though.

80CuIn

jtimbck2,
Thanks for clarifying and getting back to your origianl topic. However, I'm not sure what you mean by driving in 4th when you normally dirve in 3rd with a 5 speed.
I too have been driving 5 speed manuals for nearly 20 years and am trying to understand. For those times when I don't feel the need to travel quickly, I like to focus on gas milage. Especially the mundane travel to and from work.
So, jtimbck2, can you give me an mph reading when you would shift to 4th? Your right, 3rd is quite tall. Did you shift to 4th at 35......42mph to achieve better results?
Thanks
Al

rieskame

Do you lose all the waypoints on the navigation if you disconnect the battery? I drive 95% highway and am averaging just a tad over 17 mpg @78-85 mph. It doesnt seem to matter if i use 87,89, or 92 octane. That seems like an easy trick, but if the dealer flashed the computer, would it do the same thing?

Eric

jtimbck2

Every transmission is different; but I'm just generally talking about around town driving (in the approx. 35-45 mph range). With a 5-speed, I'd rarely shift up to 4th for those kinds of speeds; I'd just drive in 3rd. Which is what I'd been doing in the 8 because it's so smooth. I've started using 4th for that general speed range in most cases. The result has been improved gas mileage.

Simple? Yes. Obvious? Not necessarily, especially to someone who hasn't driven a 6-speed before now.

Heh -- my 500th post :-)

Ole Spiff

From reading all the threads and posts on gas mileage it appears that 3 factors affect it the most; driving style, gas quality and outside temperature. The outside temperature most likely is also affecting gas quality since I believe gas companies switch their summer gas for winter gas which is formulated differently for colder climates. I live in Southern California so we don't get the winter temp extremes here but I know back east they use different gas in winter. It doesn't seem to matter which car you drive or whether it's MT or AT.

I'm surprised at the posts that report shifting at 3k or lower shift points. If you look at a dyno graph of the power/torque curve of the Renesis engine you'll see that's a very inefficient point to be shifting. Keeping the rpms low WHILE trying to accelerate is going to cost you gas mileage...period. It's almost like lugging the engine because you're forcing it to use fuel to try and gain power since the rpm's are so low.

The optimum shift point on the graphs I saw show it to be around 5,300 rpm. That's the point where the torque and horsepower curves cross. That will give you the most torque and power the engine can deliver at the same time. If you wind it up to higher rpms you gain horsepower but lose torque. This is something you would do when you're already at speed and have mass-in-motion so top speed is now the goal rather than getting up to speed. Good for track racing obviously. Street racing is different since it's all about acceleration. If you want a maximum performance shift for acceleration in a race, shift at about 5,800-6,000 rpm so that in the next gear the rpm's START at the maximum peak torque for the next gear. Torque is what pushes mass forward. That will kick your car forward the quickest until you reach 4th gear; once you're heading for 5th gear now you can wind it out on the tach because mass is in motion and you're going for top end speed.

Around town I normally shift at about 4,500 rpm if I go by sound instead of looking at the tach so that's generally where I shift if I'm just driving regularly without pushing for performance. I always shift for performance when getting on the freeway. My gas mileage even at worst is about 18mpg. Best mileage under normal driving is around 21. BUT...again I live in Southern California where the temps aren't as cold and we don't have the winter gas that's sold back east.

To those of you shifting at 3k or lower...try shifting at 4,500 rpm as a test for one tank of gas. Your engine won't be working as hard to accelerate the car because the rotating mass of the engine is providing power instead of just using fuel. All else being equal you should see an improvement in engine temps and performance. You can still accelerate gently if you like but wait until you hit 4,500 rpm before shifting; you'll definitely notice the improvement in "kick" when you shift to the next gear. Believe it or not the engine will use less gas getting you up to speed this way.

I can't say what effect the winter gas has on mileage since we don't use it here where I live. But I bet you should at least see SOME improvement in mileage with a more efficient use of engine power and torque while shifting.

80CuIn

jtimbck2,
I'll give it a shot. I'll try driving in 4th at around the 35-45mpg range (speed for most of my commute) as well and see.
If it works, great, if not, well, it was an easy test. Trying to be optimistic.
Al

Keshav

Just a FYI. Horsepower is Torque * RPM divided by 5252 so the lines will always cross at 5252 RPM on every dyno chart.

short shifting can help gas milage if you avoid those extra fuel ports opening up and pouring in tons of gas. My GSL-SE got great milage if I shifted before ~3000 RPM becuase it kept some of the ports closed. After 3000 you could feel the power increase as the fuel gauge raced from right to left.

O.R.A.

Winter gas always makes for worse gas mileage. This might be what some are atributting to colder weather.


When I had mu WRX, I noticed something similar to what those of you that have reset your ECU have noticed. After re-setting, the car gave improved mileage and felt more responsive. In the case of the WRX, the ECU will advance or retard the ignition timing depending on the knock sensor activity and the way you drive. It "learns" what conditions of all sensors are more suceptible for knocking and retards the ignition and adds more fuel to keep things safe. Sometimes, it would learn the wrong thing and think that this everyday normal way you drive is a condition that is suceptible to knocking, so it keeps the mix rich and the timing retarded.
Re-setting the ECU clears that "learned behavior" and lets it start again.

Greg

I'll try driving in 4th at around the 35-45mpg range...

Someone posted this above. IMHO lowest rpm+least amount of throttle applied=optimum gas mileage. Leave 3rd and 4th out of it unless you need the power to pass someone or to accelerate quickly. 6th is my "go to" gear ALWAYS. After acceleration put it in 6th and leave it there regardless of speed. (unless the engine seems like it is under heavy load i.e. <30 mph. My mileage has always been consistently around 18.

jonalan

Whether I shift at 3000 or 6000, it has no affect on my gas mileage. I average around 19.5 mpg.

I disagree with your second point. For me, it's all about acceleration/handling. Speed is not as important. I enjoy getting to 65 -70 mph as quick as possible. Then, hit the cruise control. I rarely drive over 70 mph, anyway. But that's just me.

I also believe that cruising speed has more of an impact on gas mileage than acceleration or shift points. At least, that's what I have experienced so for after putting 4500 miles on the car.

Zeltar

Really? Where did this come from? So, a Ford F-350, with a torque of 350 @ 2500 RPM needs only 166 HP (350 * 2500) / 5252. Yet, it has 260 HP. Wonder what the other 100 HP is for.

Torque is a "rotating force: force that causes rotation, twisting, or turning, for example, the force generated by an internal-combustion engine to turn a vehicle’s drive shaft".

As a good example, let's use human strength. If you apply it to a standard screwdriver, you can tighten to about 8 foot pounds. Now, use some leverage with a socket wrench... and the foot pound force us humans are capable of is directly related to the lenght of the wrench. A torque wrench is usually greater than 15" long, giving one the ability to apply 60 foot pounds or more.

In a piston engine, the arm length of the crank shaft (offset from center position) provides the leverage. A rotary on the other hand... I'll leave that to the experts.

zoom44

Really that is the correct formula. what you have shown, if your math is correct i didn't check, is that at 2500rpm that truck is only making 166hp but you don't have the final drive ratio, so you can't tell what it's making to the wheels. the T in a rotory is made by rotors gears turning the Eshaft.

Zeltar

Zoom44, you have a good point. Max torque is not usually at the same point as max HP. That's frustrating. You might actually know what you're talking about.

Racer X-8

Max HP is NEVER at max. torque, it's practically impossible. So, yes, you've calculated the HP at the rpm's where you get max. torque. I wish you gave the rpm's at 260 max. HP. If you use 260 for max hp & the rpm's at that max hp as "n", you can calculate the torque @ max hp by using T=hp*5252/n You will then see that torque @ 260max hp is less than 350 max torque @ 2500rpm.

So, yes, it's really true. HP = T*n/5252 (lb-ft torque.)

Torque is not a force. It's more like a bending moment, except it's around a center, twisting. Torque = force * distance, like a bending moment of a beam. That's why it's given in lb-ft. Force in lbs. - distance in ft. lb-ft , or, ft-lb , pretty much the same difference.

Your example of a screwdriver is complex actually. The muscles in your arm act to twist your hand, torquing it, acting against the torque of the screw, thru the screwdriver. This is a muscular thing inside of your arm, controlled by your brain. Certain muscles actual produce the forces which creat the torque around where you want the center of rotation to be (the screwdriver).

Your 15" long torque wrench is a good example. The longer it is, the less force from you is required to produce the same amount of torque. And visa-versa.

Your crankshaft is another classic. The "offset from center position" is the distance, the force from combustion, pushing the piston down, or the rotor around, is the force. Actually, it's all very dynamic & the forces required to suck the intake in & compress the fuel/air mix just prior to combustion & push the exhaust out, from the other cylinders, or rotary chambers, subtract from the "net" torque coming out of the crankshaft. Yeah, best left to the experts...:D

rxeightr

Agreed. After 7,500 miles this is what I have concluded as well.

Of course, I do not get involved with much stop-and-go city driving that might skew my results.

Avg 20-22 mpg.

eclps0

i have 10,000 miles and i finaly broke 20 mpg with babing the crap out of her. why cant i get better mpg.

Zeltar

I acquiesce to the torque formula. Found this website which has many interesting auto related formulas:

http://www.prestage.com/Car+Math/Car...s/default.aspx

Thought you may be interested.

shift_zoom8

Ole Spiff, what you say about torque curve seems to be consistent with what I'm seeing. My current tank I'm shifting between 5000 and 6000 rpm and I'm not seeing too much of a dropoff in mileage, at least so far. I'll continue to test this hypothesis.

Ole Spiff

Glad to hear you're experimenting shift_zoom8. It's a crying shame to have a wonderful car like this which is such a blast to drive, and be driving it like a granny buick to try and get gas mileage. Like I've said, I shift at around 4,500 rpm or a little more as an average, I do NOT baby the car for mileage, and I use 87 octane regular gas. I drive 50/50 street/highway and I just got 256 miles on a 13.1 gallon fill-up. The car is running great and I'm looking forward to crossing the 9,600 mile mark on the odometer to see if the ECU change will make things even better. I have 7,600 miles on it now.

Something that somebody else posted I agree with which is cruising speed affects mileage. When on the street I'm usually in 5th gear once I'm up to speed; 6th gear if I'm over 50mph. I can always downshift if I need to accelerate quickly.

The main thing to remember is your car is a mass of about 3,000 lbs (plus you, whatever you weigh). It takes power to move that mass. Combustion engines convert exploding fuel into rotating motion which, through gearing, creates torque which drives your vehicle forward through tires contacting the ground. Basic stuff. To learn to drive your car efficiently, you need to use the gearing to take advantage of the flywheel effect in the engine so you use the least amount of fuel and still get good performance.

Wind and road contact friction generate the resistance that is always trying to slow down your car. You overcome this with a combination of fuel usage and gearing. Gearing is free, fuel isn't. Use fuel and gear shifts to get that mass in motion until you reach a steady-state speed; then use the lowest gear you have to maintain that speed. Wonder how Corvettes get 30mpg on the freeway? At freeway speeds in 6th gear the rpms are about 2,500.

When coming to a complete stop don't downshift; put it in neutral and use the brakes. Not only will that help gas mileage but brake pads are cheaper to replace than clutches and transmissions.

Efficient use of the gear ratios and rpms will get you the best mileage you can while still enjoying the performance of a great car like this.

Racer X-8

I concur, Ole Spiff. From what you wrote, our driving styles seem to be identical. I get 18mpg normally, 21 on a trip. It got a tad better since new. I have some 3,300 miles on her so far...still a baby.

A fuel mpg monitor would be very interesting to have. With no fuel return line, I would think that it would have been a piece of cake to add a monitor.

cruzdreamer

I have the automatic too...dealer said don't worry about it until you at least have 5000 miles on it. Then a gentleman around 60 ish at the gas station noticed my car and started chatting with me about it.....I mentioned gas mileage was bad and he said I may not see it get better until I have anywhere from 12,000-24,000 miles on it. He seemed to know something about the rotary engine. So we shall see....that seems like a long wait but I bet we will get there in no time! I think weather has a lot to do with it...cold ,damp conditions and breaking it in....my theories from a person who knows squat about rotaries!:]

XLR8

Arggghhhhhh! If you bought the car for fuel economy, trade it for a Toyota Prius. It's a sports car, for Pete's sake. The author of the initial post has not learned how to drive a 6 speed. If you buy a car with 6 gears, there is a reason. The reason is not to slowly creep up on 70 mph. It's to make it scream. I agree that first and second gears are all that are needed to make it to sixth gear. However, that being said, third gear is a lot of fun, too. It's a good passing gear on the interstate. Third gear is kinda like a seven iron (if you golf).

mikeb

If the sticker on the car said 15 MPG I wouldn't complain
but it said 18 to 24

O.R.A.

It's not about getting the fuel economy of a Prius or not. It is about all the hype of the Renesis being such an improvement in all areas, INCLUDING fuel economy, over the previous 13B.
It is about getting a fuel economy that goes along with the power and performance of the car. About meeting the expectations.

If the expectation, as presented by Mazda, is that the car is supposed to give an average mpg of 21 mpg, then it is reasonable for people to expect to get something close to that number if they want to.

You sound like the people that say that the RX-8 can't be a real sports car because it has 4 doors and more than 2 seats.