Fuel Economy on Stock K8

[MrMazda92]

Hey guys, I searched around a bit and I found some ancient posts, but nothing recent on the topic of fuel economy.

I'm poor and tend to gas up whenever I have money and realize I need gas. Usually at about 1/4 tank on my gauge(more like 1/2 the actual tank)

Anyways... My mileage is probably affected by where I buy my gas, but here are some numbers for you.

Best around town daily average for 1 Tank - 27.4 MPG

Worst around town daily average for 1 Tank - 20.2 MPG

Best Freeway Average(Eugene[Oregon] to Portland[Oregon], then return trip) - 30 MPG(Not exact due to financial issues upon fillup, but within 1-2 MPG)

Worst Freeway Average(Eugene[Oregon] to Battleground[Washington], then return trip) - I didn't write stuff down back then, but I did use almost 2 full Tanks.

The bad freeway average was when I first got my car... about 2 weeks into driving it. It was the first manual I ever drove more than once or twice, in other words I couldn't revmatch or downshift if my life depended on it.

I feel that I get damn good mileage around town... I do typically shift between 2-2.25k RPMs though. Also, I'm VERY good about coasting when possible. Saves my gas and my brakes, can't argue with that!

As for the freeway, I drive about 75-80 usually in a 65. 5th gear in an Mx3 puts that at roughly 3,750 - 4,000 RPMs.

[_-Night-Shade-_]

When I had my K8 I got around 30mpg mixed city and highway. That's about 500km per tank (always filled up about 40L). I double-clutch on downshifts and turn off the car if I know I'll be standing for more than 20 seconds. Shift around 2.5k and higher if there's more load such as quick acceleration and going uphill. I don't believe in the idea that different vendors have better fuel, it shouldn't make too big of a difference. I always used and still use 87 octane (which has up to 10% ethanol here). Even with the KL-ZE the compression still isn't high enough to cause predetonation if running N/A. It sounds like you're almost getting what I used to get so everything seems to be in order.

[edger0587]

gi think on average, combined driving in city/hwy yields about 27mpg, regarless of where I buy the gas. the only mods my car has are some pretty decent spark plugs (if you can even call that a mod) and a ram Air intake. The best fuel economy i've ever experienced was on my drive from Fresno, CA to Seattle, WA last summer. In Oregon, with their slower speed limit (55, rather than 65 or 70 and I actually stuck to it for some reason), I averaged ~37MPG on highway alone, which seemed high to me but my next fill up confirmed these numbers.

I was watching an old motorweek video on youtube for the review of the 92 MX3 GS and their MPG numbers surpassed the claimed MPG. here is the link http://www.youtube.com/watch?v=YNa1Q4i8RtQ&fmt=18" onclick="window.open(this.href);return false;

[davmac]

Your gas mileage is quite good. Compare to the current EPA estimates of 20 - 26. I don't have any hypermiler suggestions - mainly because I'm too lazy to shut down / restart, draft everywhere, drive no faster than 55, etc. Still my klde delivers 27 - 28 mpg combined city / hwy. I wouldn't mind better. Does driving 55 mph really deliver 35 mpg? That might almost be worth it ...

[MrMazda92]

@Night Shade
I'm pretty good about coasting when I don't need to accelerate, such as if I'm downtown and there's a green light WAY ahead I'll coast because speeding towards it usually ends up with me braking hard and then sitting. With the mileage I'm getting now, would it be worthwhile to double clutch when I downshift? I DO downshift a lot, and I can double-clutch pretty well. I just never got in the habit of doing it during normal driving.

As for shutting the car off, is it a crap legend that you use more fuel starting it than letting it idle? I think it'd depend on the duration of the idle, but 20 seconds seems a little short for me, I don't know though. I got about 15-19 MPG in my Mercury Mountaineer when I drove it more often, that was pretty good for an SUV. Stupid auto tranny too! Boring. ;(

@edger0587
That's pretty close to my range. I drive carefully 90% of the time so I don't feel bad about the 10% where I shift at 5,500 to pass some D-Bag in his mom's civic. There aren't many performance cars in Eugene(Unless you consider straight off the lot New-Muscle)

Also, you're right about the slower speeds. I think it has to do with our engines loving the high RPMs, and the gearing of 5th gear. If I drive 55 in 5th gear, I'm at about 2,750 RPMs. Also, there isn't that much drag. If I drive at 70 in 5th gear, that's 3,500 RPMs with a lot more drag.

@Davmac
I'm proud of my mileage, but I wish I could get better on the highway/freeway. I feel it DOES help to go slower when it comes to freeway driving.

[_-Night-Shade-_]

Technically double-clutching should waste a tiny bit more fuel because you're revving the engine for that split second. But it's such as short moment I would say it's negligeable. Either way I'd rather pay a bit more for fuel than have worn out synchros. Shutting the car off when you stop CAN waste more fuel to an extent but only to a certain point - that's why I said 20 seconds, by roughly that time you've spent more fuel idling.

PS - I really want to buy a vacuum gauge soon, that way I'll be able to figure out at which rpms and gearing the car is more efficient.

[MrMazda92]

I thought it might be worse for mileage, but you're right about it being easier on the tranny. I forgot how smooth I can downshift if I double clutch... After reading your posts, I downshifted about 50 times just to practice it and get a feel for the difference. It took about 10 DC Downshifts to get used to the movement, but I love how smooth it is. Thanks for reminding me!

[mitmaks]

I'm averaging about 23-24 city driving and 30mpg on highway.

[slayer322]

I was lucky to get 450Km to a full tank lol, shifting at no more then 3k and rev-matching all the time

[mikeinaus]

I thought it might be worse for mileage, but you're right about it being easier on the tranny. I forgot how smooth I can downshift if I double clutch... After reading your posts, I downshifted about 50 times just to practice it and get a feel for the difference. It took about 10 DC Downshifts to get used to the movement, but I love how smooth it is. Thanks for reminding me!

what exactly is double clutching? i googled and came across this

Double clutching
A technique used with older manual transmissions that do not have synchronizers (a "crash box" transmission). The driver puts in the clutch, moves the shifter into neutral, releases the clutch, and then puts the clutch back in and shifts to the next gear. This extra step allows the engine speed to match the speed of the gears, so the shift is smoother and prevents excess wear on the transmission.

that doesnt really seem like it would do much to me. if anything wouldnt the rpms drop even more in that second your in neutral and be harder on the tranny? or are you supposed to rev match when its in neutral with the clutch out?

[Sleeper6]

honestly the biggest issue Ive had with fuel economy is getting Non ethanol fuel. When i can find it (kwik fil is the only place around here) i can pull 34-35mpg however when I have to run that 10%ethanol garbage it plummets to 28mpg

[_-Night-Shade-_]

I thought it might be worse for mileage, but you're right about it being easier on the tranny. I forgot how smooth I can downshift if I double clutch... After reading your posts, I downshifted about 50 times just to practice it and get a feel for the difference. It took about 10 DC Downshifts to get used to the movement, but I love how smooth it is. Thanks for reminding me!

what exactly is double clutching? i googled and came across this

Double clutching
A technique used with older manual transmissions that do not have synchronizers (a "crash box" transmission). The driver puts in the clutch, moves the shifter into neutral, releases the clutch, and then puts the clutch back in and shifts to the next gear. This extra step allows the engine speed to match the speed of the gears, so the shift is smoother and prevents excess wear on the transmission.

that doesnt really seem like it would do much to me. if anything wouldnt the rpms drop even more in that second your in neutral and be harder on the tranny? or are you supposed to rev match when its in neutral with the clutch out?

Dude modern cars have synchronizers between every gear so rev-matching isn't necessary at all, it's completely optional. There are vehicles that still use unsynchronized gearboxes however, most notably large commercial trucks because they have like 18 gears and would experience crazy losses through the drivetrain if all the gears were constantly in mesh (synchromesh). That and race cars (because they want as little power lost through the drivetrain as possible). Having said that, double clutching can still be used in synchromesh trannies to prevent the synchros from being worn out as fast, as you're basically doing their work for them. The mechanics behind it are pretty complicated, I couldn't understand it right away myself, you need to read up on how manual transmissions work and how the input/output shafts get affected when you change gears.
But the PRIMARY reason for double clutching on regular cars is when you're taking a corner at high speeds. If you're a good driver you will downshift before the turn (or during) so you can accelerate out of it right away. If the car is already under stress because you're taking that turn going as fast as you can, the slightest jerk of a downshift will unsettle it and you will lose control, that's why you double clutch to make that shift as smooth as possible. You will see if you try it yourself - if you do it right the shifter goes into the gear like butter, you barely have to force it (the reason for it is you've matched the speed for the synchros and there is no resistance).
Don't forget that there IS a difference between just rev-matching (with the clutch depressed) and double-clutching (rev-matching in neutral).
Now I'm no professional racer but I think it's a good habbit to get into and will save the synchros like I mentionned.

[mikeinaus]

so do you rev match when the car is in neutral with the clutch out or does the car do it by itself?

[_-Night-Shade-_]

Lol no man, here's how you do it: let's say you're in 4th doing 60km/h (about 2.5k) and you want to downshift to 3rd, which would be around 3k or slightly above. If you just clutch in and downshift and clutch out, when the clutch engages the car will jerk because the engine will be sped up to match the speed of the tranny. Rev-matching (giving it some gas with the clutch in to get the RPMs up to what they would be in the lower gear) will get rid of the jerk when the clutch engages but the synchros will still be doing their work. So to properly double clutch here's what you do:
Clutch in --> shift from 4th to neutral --> clutch out --> rev up to what the RPMs would be in 3rd --> clutch in --> shift from neutral into third (should go in like butter if you did it right) --> clutch out --> you're done.
This is all done very quickly and should take half a second, you can YouTube it - there are some nice videos of pro drivers doing it while racing and you can see how quickly they do it.

[mikeinaus]

yeah that makes sense. thanks big guy...