Well I can get a good deal on rear end with 4:11 gears it has new pads, ring pinion and I think new rotors. Its from a buddy of mine he says he got it out of a trans am but I dunno what year, am I going to have trouble getting this to fit it its not a 3rd gen rear? Also how do you think the 305 TBI is gona feel with the 4:11's

 

Well the year matters quite a bit on that rear. Anything before 82 and you are really SOL, 82-84 are standard fittings which aren't that bad, 84-88 would be alright if it didn't have the delco brakes, the 89-92 would be prefered, and the 93-02 would work well too except you'd need different wheels. Also the stock 305 tbi with t-5 will be a terrible combo with 4.11 gears, have you seen where the tach red lines at (it really stops making the power there)? You'll be in and out gears and then stuck cruising 70 mph at 3xxx+ rpm.

 

I've got 3.89's on my 305/t5/ford 9". I would definetely NOT go with 4.11's! the ..stock.. 305TBI makes 255ft/lbs @ somewhere in the low 2000RPM's and makes 175hp(eww thats low) @ 4500RPM's. I could be a little off with the data but you'll get over it if I am. I usually bring the RPM's to 4000 through first and second, than third and fourth are the real pulling gears. But thats me, shift how you want. BTW, if you do a lot of highway driving dont even think about going above 3.73's. Im @ 3k rpms going about 70, so 4.11's will increase your RPM's a lot more than that! Plus, I'de like to see a thirdgen get excellent traction /w 4.11's.

 

I just wanted to chime in about the very last part of your post. Using the simple RPM calculator that is linked off the TGO homepage, there is only about a 200 rpm difference between your 3.89's and 4.11's at 70 mph. Using a 5th gear of .75 (wasn't sure what year T-5), tire radius of 12.8", 3.89 and 4.11 rear gears, and a speed of 70, the rpm's were about 2700 and 2900 respectively. If you've got the .63 5th gear, you're going to turn lower rpm. Highway mileage should not be a concern in going to a lower gear, whether or not the gear will work with your engine combination should be.

 

Im pretty set on getting them, im going to be swaping in a 350 later on with a t56 and superchager and this rear is a steal at 300 bucks

 

Its a 91 T-5 WC