phish

I will preface this by saying I have no idea about engines or how and what I should do when it comes to classic muscle cars. So any help would really be appreciated.........Here is what I have......65 coupe bored .30 over 289 -4 bbl...The engine has been completely overhauled and makes 225hp to the ground. I just put in a new t5 transmission. My question is what size rear end should I install. What are my options with pros and cons. The original rear end is starting to go so I have to choose relatively shortly............Thanks !!

Starfury

Assuming you have an original V8 car, you should have an 8" rear. Honestly, with the power you're putting out, that should be just fine.

All you need are new gears, a limited slip differential (if you decide you want one), and standard rebuild parts. If you want, you can even get all of this in a complete, ready to install pumpkin so you can do the whole job in your backyard.

For gearing, we need to know what the intended use of the vehicle is. Although with a T5, you're probably going to be looking at between 3.55:1 and 4.11:1.

For the diff, if you decide you want limited slip, I'd recommend a Detroit TrueTrac. It's a worm gear (as opposed to clutch-type) diff that instantly transfers torque to the wheel with the most traction. Several members here have this type of diff and are very happy with it.

GT350R Klone

I agree with the 8 inch, spending $ on a 9 inch would be overkill and a waist of $. Since this is a street car and you have overdrive, I would go for 3.55-3.73 gears and limited slip.

Adrenolin

Save yourself the headaches and as Starfury stated above.. order a Detroit TrueTrac setup with gears between 3.55 & 4.11. If you do a lot of highway driving pick the 3.55. If your looking for fun and not concerned with fuel mileage go with the 4.11s.

You simply cannot beat the Detroit TrueTrac! Here is what we're talking about. Add gears and install it. Give them a call (or any other vendor) and order it with gears as above per your choice.

phish

So is Detroit TruTrac a good brand?? also it looks like you guys are saying between 3.55 and 4.11's.......I do a fair amount of hwy driving and I also like to speed around a good bit.....so if I pick the gears in the middle (3.73) do you guys think that would be OK??............thanks in advance

Gun Jam

Yes the TruTrac is great I run one daily driven for about the last 2 years and its top notch. Totally quite and smooth even when all available HP is being used to burn or grip both tires.

If you do a lot of highway driving I would recommend the 3.80 gear set with your t5. I dont even know if you can get 3.73s for an 8". But if you get the 3.80 gear set and you have the .68 overdrive t5 (Which is very likely the other option is .63) and you total rear tire height is 25" then

@2300 RPM you will be going 66 mph in 5th
@2600 RPM 75 mph in 5th
@3000 RPM 86 mph in 5th

I run 3.80s on the freeway all the time for extended periods (1.5 hrs or better) I find that my v8 run really well at about 2500 RPM I think that's probably very close to optimal cruise RPM

If you are going to go through the trouble of switching gears you might as well get the lowest ( Example 4.11s are lower than 3.80s and will provide better acceleration but result in higher cruise RPM which after 2500 RPM will result in less fuel mileage) possible gear that still meets your needs (Extended periods of high speed freeway travel) I think you'll find 3.80s to be a good match.

-Gun

tx65coupe

I recommend going with traction lock limited slip. I also agree on keeping the 8 inch and going with 3.50 to 3.70 ish gears.

gothand

The first thing to consider is which T5 you have, specifically, which gears.

http://www.allfordmustangs.com/Detailed/349.shtml

That will go a long way towards choosing a rear gear set. Also, consider your tire diameter. My advice is to stick to about a 3.5:1 gear ratio for a good balance between street and strip.

phish

I will find out tomorrow what type of t5 was put in......as far as tires go, I will be upgrading to 17" wheels......from what i have read so far I am leaning towards 3.55 or 3.73 gears.....does this sound good??....thank you in advance, u guys have helped a lot

Fordication

There goes a good rearend.