why do 3400's get better mpg than 3100's?

[robertisaar]

no, just the blend of fuel that gets delivered.

technically, yes your computer does richen the mixture based on IAT values, so you'll always lose economy when the air is colder...

something to remember: on a stock tune, except for when its warming up or in PE mode: the ECU is stuck with a 14.7:1 AFR, no higher, no lower. thank the EPA for that one...

[Raffaelli]

My moms 4cly 89 Mustang auto = 17~ mpg
My own 5.0 86 Mustang GT auto= 22~ mpg
later with a 5 speed swap = 24/25mpg

The bigger engines cruise with much less throttle position and load on the engine. A pitifully small mill doesnt have the balls to get any power or mpg out of. (not sayin a 3.1 is small)

Plus manually shifting the gears helps quite a bit.

[robertisaar]

those 2.3 4 bangers were horrible... not enough even to move something as light/aerodynamic as those years of mustangs. what kind of gearing though?

as for the bump in economy you got switching from auto to 5 speed: while manual shifting can help, most often, its the steeper gears and fact that manual trannies lose less power compared to an auto.

recently, some autos are losing less power than manuals...

[no_doz]

what afr do most people around here run on an NA engine/what would be the lowest afr youd want for max mpg?

[robertisaar]

this is for both the MC and GP

normal: 14.7
PE: 12.5
Lean Cruise: 16.2

[andrew383]

my GP gets 30mpg ~ at 80mph

hows this for mpg-i was towing about 4k from TX to IN in the ss at 80mph

[robertisaar]

i've still gotten 30MPG at 90MPH before... its crazy what a slick body and the right combo of gearing/engine size will do...

[nixtux]

That's about what my 1973 GMC Super Custom does with no wind @ about 70.

With a head wind, about 6-7.5MPG. With a 18 gallon tank, I had to fill up
every 90-100 miles.

In town, driving nice, I'll get about 65 to a tank. Not driving nice, 40-50.
It also has a hard time keep traction between 0-45MPH at WOT. As long
as it's not hot and humid anyway. 30-50F it will break between 2nd and
3rd on dry tar. Over 50F and humid, just between 1st and 2nd.

A real neck breaker that truck is and rebuilding the carb, wow, what a diff.

my GP gets 30mpg ~ at 80mph

hows this for mpg-i was towing about 4k from TX to IN in the ss at 80mph

[2.8 Grand Prix]

My '87 Mustang that I used to have got around 24-27 MPG hwy.
It had a '89 2.3 with an auto tranny.
I think it had 3.73 gears.

Of course I never had it out on the road very much. About a month after I got it, I discovered a battery leak that I couldn't find. It drove me crazy so I sold it, well actually I traded it for my Grand Prix.

[robertisaar]

My '87 Mustang that I used to have got around 24-27 MPG hwy.
It had a '89 2.3 with an auto tranny.
I think it had 3.73 gears.

thats what i was looking for...

3.73 on a V8 car is a fast gear, but on a 4-cylinder car, that much reduction is needed just to move it fast enough to get out of its own way...

if you could keep it in top gear with lets say 2.97 gears without going into PE, it would probably pick up between 5-10MPG from that alone...

[GLHS]

What is lean cruise?

[robertisaar]

at low load and a decent speed, the ECM leans out the AFR from 14.7:1 to whatever you want it to. i like 16.2:1 myself...

[Azrael]

After switching from 2.93 to 3.29 gearing, I haven't really noticed a difference in mileage although I wasn't really paying much attention to it before. Right now with 90% highway driving I average about 8.5-9L/100Km. I dunno what that translates to in imperial. Considering I'm still on my original timing chain, it's stretchedness is probably also contributing in some way.

[Rhedalert]

26-28MPG, not bad!

[3400-95-Modified]

Lately I've averaged 24 in my .030 over 3400 in my Beretta with a 3.06 ratio. It's not that shabby for a car of that age to get that mileage especially when its town road driving, and not highway. I know I can do better.