2.80's--4.11's gas milage?
 

i am going from 2.80's to a 4.11 set. i am somewhat confused should i see an increase or decrease in gas milage.

the rpm's will be higher but theres less strain on the engine so im not sure what way it will go. thanks. comments questions welcome.

It'll decrease cause it will be so much more responsive that it will be hard to keep a lite foot on the pedal. also you have no overdrive so will be buzzing on the freeway.

Less
 

Going from 2.80 to 4.11 will give you less mileage and will spin your engine pretty tight on the highway. My 3.25's with a C-4 turn the engine at 3000 RPM @ 70 MPH (235/60/15's). 4.11's would turn in my car at almost 3800 RPM @ 70 MPH. 2.80's would turn about 2600 RPM @ 70 MPH in my car.

Rev

ok im still confused one person said it would go up the other down.

i dont really drive freeway so forget about that and what if i dont have a led foot and try to drive slowly to get better gas milage.

mechanically speeking what should it do?

Both posts above said your mileage will get worse. It will. The bottom line is your engine will be turning at higher rpms for the same speeds. In order for an engine to turn higher rpms, more fuel is required. Your gas mileage will suffer, but it won't matter. You are going to be so busy trying to peel the smile off your face, you won't even notice the difference in fuel mileage.

:)

Take care,
~Chris

ok thanks guys.

see my post under "C4 with 280s"

Here's a couple of charts showing the RPM differeces at 60 MPH with varying tire heights, gear ratios, and with and without an overdrive transmission:

http://www.ultrastang.com/Rearinfo.asp?Page_ID=3

If you put 4:11's in your car there's no way you can worry about gas mileage. You'll be getting around 10mpg. If you wish to get the best of both worlds, performance and gas mileage you'll need a five speed transmission; one with an overdrive fifth gear.

With my old 2.80's i was getting around 8.4 mpg. what do you think i should expect if i put 3.55's in my car? will there be that big of a difference in gas milage?

Is this a test? Your signature line says that you have 3.55 gears. Since your mpg is so low, I suspect you spend a significant amount of time this your right foot close to the floor. In this case, I don't think you will change mpg much.

well actually i dont have the 3.55's yet. my car is up on jackstands because i took my old 2.80's out and found that there were 10 broken teen on them. So i bought 3.55's and just put it in my signature eventhough the gears are still in the mail. i was just wondering how much lower my mpg would go from the 2.80's to the 3.55's.

Also i do like to go fast and thats mostly the reason i bought the mustang and had an engine built just for my car but i think i also need to work on the carb a little. i think i need smaller jets for it because i lose power after about half throttle. i think its just running too rich but im waiting to get a air-fuel sensor anyway so thatway i can be for sure and get everything right without guessing. sorry for the confution.

I have 3.55 with a T5 and Edelbrock performer stuff. I think the acceleration is "more than adequate" (term used by Rolls Royce). I think you'll be very happy with the 3.55. To a large extent, your economy will be a function of your right foot, assuming the car is properly tuned.

If you are trying to get good gas mileage and great acceleration there is no such thing, unless u have a fuelie with a 5 speed. When u have a 60s car like that unless its your daily driver mileage shouldnt be a huge concern, get the 4.11s and get a big smile on your face, just dont go on the highway, it will rev too high. You'll be happy with the gearset, I just helped my brother put in 4.11s and a 5 speed in is 67 mustang, and it pulls like crazy, but the difference is hes got fuel injection on his 289, so he actually gets decent gas mileage

so your saying

a mustang '66 5 speed don't go on the highway because mileage will be bad....


plzz explain

is the gearing of a manual geagbox that close ratio....
I thought the gearing of a 5-speed would be at leased the 5th like a overdrive or something

is a automatic than better for your mileage... i thought the other way around....

no I was assuming that the 66 was a C-4, with a carbed 302 or 289 with a C-4 and 4.11s will not get good gas mileage regardless on the highway, due to the revs.
It might be a little better with a 5 speed or an aod, but it wont be much better with a carbed motor, you'll be looking at 11 -14 mpg at best with an overdrive, and thats if u dont ever get into it, otherwise your gonna be at 5-8. I have never cared about gas mileage on performance cars like these, with carbs it should be somewhat expected that your mileage will be less anyway. Is the motor built up in this 66?

Overdrive
 

4.11 gears in an overdrive transmission, either auto or 5 speed, will be like a 2.80 without overdrive on the highway.

4.11X.7=2.88.

Rev

I haven't driven my '65 long enough to break it in yet and have not truly checked the gas mileage. It is a 5 speed 3:50 gear set car and I can tell its getting good gas mileage already. The acceleration is good enough for me...I mean I'm quite happy with how the restoration project came out.

Oops, wrong picture posted... Here's the one I meant to xmit.

what is a good mileage?

Ltr/Km