zmetalmilitia

I am looking on getting a new 3rd member for my 9" rear. I want something good on the streets but also good on the highway. Probably street driving, 75% of the time and the other on the highway. I am thinking about either 3.50 or 3.75 or 3.89. It will be posi and have around 400+hp. Planning on a 5 speed manual transmission, 17" wheels. What would be best? thanks.

my77stang

without overdrive i would say 3.50 for highway and 3.75 for city only, with overdrive i would say 3.75 on highway, 3.89 or 4.11 city

if you went with the 3.75 you'd be quite happy

Starfury

With a 5sp? Go 3.89's, or even 4.11's Unless you're doing long distance stuff on the freeway, you'll appreciate the shorter gearing.

zmetalmilitia

Yeah I was leaning towards the 3.75, but considering the 3.89. My first coice was 3.50, but now it's between 3.75 and 3.89. Is there that much of a noticeable difference bewteen the 3.75 and 3.89?

Aussie66Fastback

you might wanna consider some decisions on the 5 speed before the rear end. sorry if you're already a step ahead of this

2 things

1) you want the box that can handleyour [unspecified] torque (which may or may not be a standard T5)

2) you want to know the ratios, particularly for 1st and 5th.

examples

too lowratio 1st with a 4.11 means early change (eg '84 SVO T5, engineat 5000rpm = 21mph).
too highratio 5th with 4.11 means still revving fairly high at highway speeds (4.11 with 0.87 5th = 3.57 final drive).
too low in 5th with 3.75 meansless pull in 5th (3.75 with 0.69 5th = 2.58 final drive)

zmetalmilitia

I'm not sure what exact transmission I will be getting, other than the fact it will be a 5 speed with overdrive. I guess I'll have to find something that will handle the torque and get the gearing right. The torque will be somewhere in the same range as the hp, 400-450 or so. I assume there is a transmission that will fit my application?

67t5ponycoupe

I have the T5 with 3.50's in my nine inch and I really like it. First gear is just a little low for my liking but the engine runs at 2200 rpm on the highway in 5th doing around 75mph. Really low gear sets like 4.11's are not the best choice for a standard transIMO. With an auto they are ok because the trans will shift for you.

67mustang302

Low gears are good for manuals if the transmission has the right gearsets in it. You need to know what trans you're gonna run and what the gears are before you get a ring/pinion set. If you go with 4.11's and have a trans with something like a 3.33 1st, you'll have a totally useless 1st gear on the street or on the track, no traction whatsoever not to mention shifting outta first about 0.5 seconds after the clutch is engaged. Too high a diff gear with too high an o/d and you may not be turning enough rpm on the freeway to use 5th without bogging the engine somewhat(dependant upon the engine build) unless you're speeding. Try explaining to a cop why you were doing 85 in a 65 zone because of your gearing, I doubt he'll have sympathy for your plight.

Starfury

The G-Force T5 kit has a 2.94 1st, 1.94 2nd, 1.34 3rd, 1.00 4th, and an optional .59 or .73 5th gear. When I get to it I'm probably going to opt for the .73 5th to narrow the gap between 4th and 5th. Freeway mileage is not a huge concern for me Won't be any worse than it is now, turning 3300 @ 75 with my 3sp.

67 evil eleanor

Tranny ratios, wheel and tire size, will come in to play. For me, I have both 3.70'sand 3.50's in cars and for highway use, the 3.50 is my favorite, more so whenhooked to a tremec tkowith a .68 final. It helps if you have some hp to push these along.