hey guys, i have a 289 automatic. (only an auto till i can convince my parents to let me get a 5 speed) it has the stock rear end and gears (what ever ratio that is) I want some gears to make my car quicker off the line. what kind do i need? whats the fastest 0-100 ? are 4.10s ridiculous for highway driving? 3.73s? i do mostly stop light to stoplight driving but a few times a week i have to get on the high way for a good hour or so. also, what are the stock gears, and what is the stock 289 1965 rear end size so i would know what size to look for. any recommended brands? thanks guys, appreciate any help i can get.

 

stock gears are ~2.80's (I think the exact ratio is 2.78?). With an automatic I wouldn't go any higher than 3.55's if you want to maintain decent highway driveability. 4.10's will be taching waaaaaay to high, not to mention you'll burn through some oil and gas just making round trips with the engine spinning that hard. 3.55's give good off line pulls, and imo, still provide decent driveability @ 60-70mph.

edit: you'll want to look for gears that fit a ford 8"

 

get a traction lock diff with 3.00 or 3.55 gears. get some roller tips for your heads, ive heard itll take a second off the line. or so some person says.

 

I'll third the 3.5x gears.

Roller rockers won't make a huge difference by themselves. Roller cam would make the most difference, but that's a bit on the pricey side.

A stall converter would also increase your off-the-line response and a shift kit would help the tranny performance and longevity. On the longevity side, add an external filter and cooler for your auto.

 

thanks, when you say 8 inch rear do you mean straight up 8 or 8.8? thanks
and what kind of shift kit do i need to look for (stock c4)

 

Our old stangs have 8 inch rears. I would go with a 3.25-3.55. Im not going any higher then 3.55, because my car already runs high to me with 2.78 rear. I turn 3000 rpms at 75.

 

I've got 4:11's in my truck and I run it at about 60 everyday for about an hour. It really is pretty hard on it. I only get 9mpg

 

im probaby going to keep my stock gears at 3.00

even though alot of you wouldnt but, i get off the line just fine with my stock gears.

 

short tires that fit a Mustang are quite different from truck tires and 4.10s. It makes a difference in cruise RPM as to what tire is on, but it doesnt change the rear end ratio.

Easy way to find out what rpm you need to turn a certain mph with a certain gear is this..


(gear ratio x 336) / (tire daimeter x RPM) = mph

4.10x336 = 1378 divide by 25" dia x 3000rpm = 75000 = 54.4 mph

(3.55x 336) = 1299 /
(25 x 3000 ) = 7500 =57.7 mph

Check out what a taller tire does. We'll throw some 27.5" diameter tires on it.

(3.55x336) =1299 /
(27.5x3000) =82500 is 63mph at the same rpm.

So .6 change in gear and 2.5" taller tire is equal to 10mph difference at the same RPM.

 

what about a shift kit?? does anyone have one? i have a 65' 289 with a C4 auto and would like to know where i can get one?