I was just wondering....My Car is a automatic and at 75MPH it turns about 3,000 RPM on cruise...I am still getting 21.04 MPG but I think someone installed a 4.10 gear....does this RPM sound about right? I have the 4L60 Tranny and standard Z28 tire size.
Would I get much better mileage stepping back to a smaller gear like a 3.42 or so? Or is the change not worth it? based on mileage/cost of change/and reprogramming the speedo...etc...What kind of highway mileage should I expect?

 

well at 70 im running 2000rpm. and ive got 245/50/16s.

 

i doubt the 4.10 gears were installed but they may have put in 3.73s. i run about 2000 in my dads V6 automatic

 

with 255/50/16's=around 1500 at 60 2000 at 80
245/50/16/s= around 200 rpm faster on both
my spedo is off, i know, with the 255's its 8 miles an hr off at 81
lol got to love cops!!

 

just below 2000 at 70-75 no cruise control.........getting about 22-24 mph....got a 97 z28 auto...........

 

70 mph i'm at about 2200 or so with an auto and the GU5 3.23 gears.

 

So I most definately have deeper than 3.23 gears.....At least 3.73 or 4.10....I have 3.91 in my 69 firebird and it feels very similiar....But the Bird has a .85 overdrive high gear and much taller 28 1/2" tall drag radials so its hard to compare.

I found the post about factory codes for rear gears....I will check asap to see what the build sheet says in the glove box or door. But I swear with O.D. Trans and a 3.73 it should turn less RPM to me...maybe its just because the tires are so short.

 

when my camaro was stock (1998 6 speed) I was turning about 1700 rpm at 65 mph with the stock 245 50 16 tires. That was with 3.42 gears.

 

my 96' z28 does 80MPH at 2000RPM. stock tires (245/50R16 is stock right?) and whatever the stock gearing is (3.93 or 3.73 or something?) I was getting about 25 MPG going to college last year, about 4 miles on a windy raod and about 50 on the freeway each way.

oh yeah! it's a six speed!

 

At 60 I'm turning about 2200 with 3.42's? Also its an auto.