JSmith0101

iTrader: (6)

I'm curious if I will get better mileage in fourth gear, doing 62 mph, versus fifth gear doing 62. I don't want to get flamed or anything, I just want to get better mileage...

So which is better, fourth or fifth?

Terrh

iTrader: (7)

5th.

lower revs = less airflow = less fuel = better MPG.

Syonyk

Not always true. Rotary engines are annoyingly inefficient at lower RPM.

If you're turning under 3500 RPM in 4th, you'll probably get better economy in 4th. The stock ECU switches to open loop mode somewhere around there, and fuel economy goes down the crapper.

-=Russ=-

RXgirl7

i get the best milage at around 3.5k...just put it in 5th and cruise

Terrh

iTrader: (7)

when putzing around town I shift at like 2300rpm and cruise under 2k frequently... how would my milage improve if I bumped these numbers?

coldfire

iTrader: (1)

it's wierd, if i look at my SAFC AFM opening percentage, the number doesn't change a whole lot between 4th and 5th gear if the load stays basically the same (staying the same speed).
i think fuel consumption is based a lot more on load and throttle opening, rather than purely rpm, and from what i remember this is what simple physics would dictate.
hell, on downshifting you can be at 7000 rpm, but there will be basically no fuel consumption, heh...

but 62 mph in 5th gear will put you into closed loop mode using the O2 sensor, so it most definetly should get better gas mileage than being in open loop fourth gear...

homebrewer

Lets say the difference between the two gears is 1000 rpm at the e-shaft. The reason why mileage may not differ much is because the 1000 rpm difference in e-shaft speed is on 333.33 rpm difference in rotor speed. That's my theory.

slpin

iTrader: (9)

if i drive easy, i use 5th gear at around 40-45
on the mazda owners manual, it recommended shifting from 4th to overdrive at 45mph (page 3-5)

russ is wrong.

Terrh

iTrader: (7)

the "shift up" light on the tach comes on at about 45mph too (think it comes on at about 72km/h) under light throttle.

7romanstatesmen

iTrader: (1)

well, if you're at a lower rpm, you have to open the throttle more to get the same power to say, get up a hill or something. so, if you open the secondary ports because of this, wouldn't you get worse mileage (or the same) than if you were only slightly opening the throttle at a higher rpm? this is just me guessing, as i've been wondering about it as i drive around. is one decidedly better than the other?

Blowtus

higher throttle openings and same power output (ie, cruising at same speed) = better efficiency due to reduced pumping losses. higher gears are always more efficient, so long as the engine isn't lugging. diesel engines are very efficient partly because they don't have a throttle, thus less pumping losses.

Syonyk

Love your information as of late... O2 sensors creating more power up high?

It depends on the fuel maps, but it's quite possible for 4th gear to be providing better fuel economy than 5th, ESPECIALLY if 4th gear creates enough vacuum to use closed loop mode where 5th is switching in and out.

Also, the Mazda driver's manual isn't the best source of information. There are cases where guidelines aren't accurate.

If you really want to know, get some injector duty cycle measurement tools, and watch the injector duty cycle (and therefore fuel flow) at various RPM/manifold pressure settings. You might be surprised.

-=Russ=-

sar

iTrader: (1)

or you could just raise the speed very slightly, maintain the o2 sensor in the loop, and be in reasonable rpm in 5th gear- and be able to make it up hills without overloading the engine due to being in the lower power range and having more momentum to make it up said hill.

slpin

iTrader: (9)

i was kidding
and....
mazda even recommend 5th gear at speed 45mph
right there on the manual

and i have no doubt that you know LESS than mazda...
and many of us here

slpin

iTrader: (9)

ok seriously
you guys are ******* retarded
62 miles
4th or 5th gear
which would give better gas mileage

IT IS NOT ROCKET SCIENCE
it is 5th gear and Russ, you are a retard

yes, i am walking on thin ice, so what? i am in a room filled with retards. let me fall to a better place.

7romanstatesmen

iTrader: (1)

regardless of what mazda says, my car lugs in 5th gear at anything below 50 at all, and 50 doesn't allow me to accellerate or decellerate any perceptible amount. and that's assuming that i'm not going up any sort of incline.

slpin

iTrader: (9)

that means you need to get your car running so it will actually run right
just because your car runs like crap doesnt mean everyone else's does

Kahren

iTrader: (13)

why dont you try it yourself, use 4th at same speed then 5th and see which one gives you better milage. as far as acceleration goes i donno where you guys drive that 5th gear accel is enouf to pass anything on the road these days. around here i could only use 5th gear if there is noone else on the road, driving in some traffic i usually would shift down to 4th to pass if not 3rd. then again i dont always putt around as the people that are posting in thread it seems.

under 3k rpm the rotary is pretty inefficient as far as light throttle is concerned so being at the same throttle percentage at hihger rpm will give better milage. i am nor sure what the stock ecu goes out of closed loop so it could be diffrent.

Syonyk

On the S4 NA, 3500 RPM is the maximum closed loop RPM. I believe this is consistent across the FC line, but it could be somewhat different for the S5s.

The higher you can get the engine RPM without going over 3500 RPM, the more efficient the engine will be. At 3500 RPM, the engine switches to a rather rich mode, and fuel economy goes down the crapper.

Having talked to some people with standalones (tuned properly throughout the RPM range), some of them find they get better fuel economy in 4th on the highway, due to the efficiency of the higher RPM countering the slightly increased drag from the accessories/higher pumping losses.

-=Russ=-

Blowtus

my stockish s4 drives fine in 5th at 40mph... what the heck is wrong with all these cars?
as for these folks claiming better efficiency in 4th because of higher rpm... what sort of testing regime are they using? Sounds like BS to me, but I'd love to be shown to be wrong. The rotary is inefficient because it has a lot of surface area to 'bang' size. Can anyone explain or demonstrate why this means it is inefficient more so at low rpm? It still loses too much heat to atmosphere at high rpm as far as I understand.

lower gears and higher rpm suffer from more than just 'accessories drag'. Suffers from the throttle being further closed, and from higher frictional losses in the engine.

JSmith0101

iTrader: (6)

Mine drives fine at 40 in 5th, too, it just doesn't accelerate.

Syonyk

Low RPM inefficiency? Overlap.

I've noticed that my airflow meter reading (via a SAFC-II) reads slightly lower in 4th on the highway than it does in 5th. Lower airflow, less fuel being injected (at least if it were properly tuned... stupid stock ECU and firehose mode).

-=Russ=-

Kahren

iTrader: (13)

it doesnt have so much to do with the rotary heat efficiency or the overlap as it does with sealing the chamber. the sealing of the chambers is just not that good under 3000-3500 rpm

slpin

iTrader: (9)

well, this forum is pretty retarded....
notice how many people it takes to figure out there is a reason for OVERDRIVE...
and some dont even get it

coldfire

iTrader: (1)

hmmm...my SAFCII reads SLIGHTLY lower in 5th gear than 4th at the same speed.

you have a 6-port stockport engine? is your 6pi fully functional?