V6 fuel mileage

[RX8SE3P]

I'm currently averaging 28mpg in my KLZE. That's 8.4 litres per 100kms. All city driving.

Made an excel spreadsheet which figures it all out too. Might post it up one day. Currently only done about 2800kms.

It all comes down to sensors, condition of them and your engine. I have:

- A fully rebuilt straight neck ZE, hotwashed until shiny silver
- Compression is perfect
- Sensors in generally good condition
- No EGR and KL31 tuned ECU
- Headers
- New wheel bearings
- Correct tyre inflation
- Cleaned and tested fuel injectors
- New fuel pump and filter
- 2.25 inch exhaust (no cat converter)
- Mobil 1 5W-30 oil
- 98 octane fuel
- City driving (drive early in morning, traffic minimal)
- Don't thrash the engine much

Biggest difference in power I have had was my coolant sensor. It was stuffed, I changed it and not only did fuel economy get better, the car got a whole lot faster. Was clearly running rich.

[marcdh]

On my current NA setup I'm getting:
29.09 mpg US
35mpg UK
8.09 L/100km

That was mixed roads. Some 0-60 tests, some fun and most miles were boring driving.

KLZE straight neck, KL31 cams
Megasquirt - tweaked base maps
No VRIS hooked up
Headers
2.25" exhaust and no cat
35psi tyres
Long intake pipe and K&N cone
95 RON

Compression could be better, around 205.

[MrMazda92]

98 octane fuel

Wait what?

Which rating system...?

[RX8SE3P]

98 octane fuel

Wait what?

Which rating system...?

I dunno, in Australia our we basically have 3 different types -

91
95
98

[MrMazda92]

98 RON, so that's 93 AKI? I was about to get very jealous!

Makes more sense now, I forgot how many international members are here...

[Ryan]

My first tank of fuel this year in the ZE was old 87 that sat in the tank for 6 months. 8.6L/100km. Put in premium, and I see a decline of 10% already.

[mikeinaus]

must be nice

[heckdave]

With relatively easy driving around town in Phoenix, my KLZE got 24 Miles per Gallon (US) on a couple hundred miles of driving. It's in the shop now getting new motor mounts, that may make it just a bit more efficient by getting power to the wheels a bit quicker. Before the swap, my K8 was averaging 25 MPG, so I'm happy with that.

[_-Night-Shade-_]

I feel like throwing on my stock-sized 205 all season tires just to break into the 7's...

[mikeinaus]

are these city or highway?

ive given up on trying to get better mileage and just accepted my car is a pig. ive only broken the 400km to a tank mark once and that was almost a year ago with all highway driving.

im not too bad on the highway as i can probably get close to 7l/100km for a full tank on decent roads. however on the city with alot of short trips i average close to 11l or 12l/100km. i saw little improvement going with a de ecu/vaf over my chipped ecu. biggest improvement i was able to get was from the fuel mileage cpu i installed in my car. tells me instant mileage, distance to empty and a bunch of other nifty features. just from the readings i get from it i can tell im running rich. going up a steep hill its actually more efficient for my car to be in 5th at like 1800rpm and struggling then a lower gear with less pedal which doesnt seem right to me.

ps. how big is our tank? i was under the impression we had a 50l one but i see by your fillups you had a 51l fillup recently?

pps. people gotta stop bumping these fuel mileage threads. just when i start to accept mine for what it is i see this and it annoys me all over again.

[_-Night-Shade-_]

Mike, the fact that it's showing you a supposedly better reading in 5th going up a steep hill is definitely not right. What kind of fuel economy calculator is it? Especially if it can predict how much further you can go... it would have to be directly connected to the tank floating unit or something.
On the contrary I've noticed my fuel economy doesn't change much whether I do almost 100% city or almost 100% highway. The reason why it says 51L that one fill-up is because I put in 10L from a jerry can in between and didn't want to do a separate entry for it. Usually when the needle is at or close to empty it takes about 41-44L to fill up the tank.

[_-Night-Shade-_]

pps. people gotta stop bumping these fuel mileage threads. just when i start to accept mine for what it is i see this and it annoys me all over again.

Hahah, these threads are good! It's a good way to see if your car is running up to par and see where it stands against other MX-3s worldwide. I'm running a Probinator so technically I'm running a little rich myself!

[mikeinaus]

it ties into an injector pulse signal and the vehicle speed sensor. it basically works by figuring out how many injections are fired per mile then compares that to the distance travelled and how much fuel was used at fillup. it uses these numbers to figure out how much fuel is used per injector pulse, it just takes multiple fill ups to get it 100% accurate. my last tank of was off about .1 or .2% for distance travelled and i think the mpg calculation was off about .2 or .3l/100km, so its definitely getting close. as for distance till empty i input the size of my tank and it calculates it threw how much fuel was used. one feature it doesnt have that i wish it did was litres (or fraction) of fuel per minute. that would give me some useful information on figure out ideal idle speed and a couple other small things.

for example 3rd gear up a hill around 4000rpm would be using probably 26+L/100km while 5th gear at 1500rpm would probably be using 18l/100km around the same speed. these numbers arnt exact, just close to what i remember at any one time. but my cruise isnt too bad. 50kph on a smooth level road ill coast around 5-6l/100km in 5th and 100kph in 5th on smooth/level is around 6-7l/100km. hammering on the throttle in 1st nets me over 100l/100km lol.

theres nothing really left for me to replace on this car. other then megasquirt 90% of my cars electronics/ anything else that would explain it have been replaced. unless my intake is too free flowing and 2.5" high flow exhaust is too big theres nothing mechanically affecting it that i can discover. compression is also decent across the board (200ish on each) and the engine is quite clean/well maintained.

im also considering going back to my chipped ecu. the vris maps are much more comfortable and im thinking my mileage increase since swapping ecu's had more to do with my mpg ecu and driving habits then the ecu itself.

also keep in mine when i say im getting close too 11l/100km now thats with throwing the car in neutral and coasting whenever possible and some hypermilling techniques.

some other information that may be useful for people aswell. ive been experimenting with different octane fuels over the past couple months. ive been doing 2 tanks at each rating and filling up at the same gas station at the same pump and i have seen negligible mpg/performance improvements from 87 octane to 92. but then again my car isnt the ideal performer when it comes to clean burning.

[MrMazda92]

I will never get how anybody gets over 30 MPG freeway with the MX-3/Probe final drive. It just doesn't make sense, unless you're driving at 60 MPH on the freeway? Cruise control, or flat footed, I would be lucky to top that with a tailwind.

City though, I can consistently top 30, because I keep the revs low and don't floor it every time a light turns green. Looking ahead and coasting whenever possible, you can get great mileage around town, in almost any car.

Freeway though... It's just not going to happen for me, not liking it at all.

[mitmaks]

~30mpg is what I get with my K8 also.