gas mileage with 4.10s in a auto?

[Murder after Midnight]

After recently purchasing a 99 ws6 T/A, Ive decided to make my 98gt my daily driver, so most of the big things I had planned to do to the car has been canceled. However I am still considering maybe adding 4.10 gears so it wont be so slow, how bad will they hurt gas mileage I'll be doing 65%city, 35% highway.

 

[glittle75]

i have a 98gt auto with 4.10's, i get 18-20 mpg with normal driving. more if its all highway. but not much more.

 

[GaryG]

im going w/ 4.10s...mine with 3.73's got 23 mpg highway

 

[DropTopPony]

I get about 23-25mpg with the 3.73 so @ 20ish should be easy with the 4.10's.
What else did you do to the 98? I would still find a cheap PI swap atleast if you haven't already. It won't really effect gas milage much but will make your D/D more respectable when needed

 

[Murder after Midnight]

I get about 23-25mpg with the 3.73 so @ 20ish should be easy with the 4.10's.
What else did you do to the 98? I would still find a cheap PI swap atleast if you haven't already. It won't really effect gas milage much but will make your D/D more respectable when needed

Well right now all I have done is a pi intake and k&n filter. I do have the pi cams, but I never got around to installing them. I heard if you do a pi swap the car must be tuned and you have to run 91-93 octane, is this true?

 

[DropTopPony]

You don't need a tune if you use the stock PI cams/heads but higher octane is needed for the bump in compression.