1967 Cougar third member upgrade questions

This is probably an old topic but I have a 289 mildly built automatic that still has the 279 rear end. I want to change. Mainly city driving and some highway. Do I go to the 325 or jump to the 355 gears? Trac lock or Eaton true trac? Just looking for some advice and get a little more get up and go. Also with dual exhaust should I go stick with 2.25, or go to 2.5 or 3 inch pipes? I’ve had this car for 50 years and its time for some upgrades. Thanks for any help.

If you search online for gear ratio calculator or engine rpm calculator you can find out how much more rpm you’ll be at with various ratios.

I have 3.25 in most cars and 3.4 in a spicier 408w with tko powered 68.

Only you know what you’ll like the most! But, I’d recommend 3 25 to 3.5 for all around enjoyable driving while still having decent economy.

Your car likely has the original 8" rear axle if the 2.79 ratio is original. The one you want is the optional 3.20 to one ratio which would allow the engine to still perform OK on the freeway.

Thanks guys! Yes it is the original 8" rear end. So probably stay with the 3.2. But is it worth the extra $500 to go to the Eaton Tru trac? Or save the money and just get the trac lock rear end?
Whats the consensus on the size of exhaust pipes?
I appreciate the comments.

I have a 3.55 locker rear end in my 67 with a 351w and a T5 Transmission. It drives well on the freeway, not really high in the RPMs. Ny favorite is burnouts and donuts! Good luck with your research

I’ve added truetrac to two different vehicles. Worth the money and so smooth on turns!

The T5 adds an overdrive which allows the car to use the higher number without sacrificing highway use. khack18 doesn’t have overdrive so using that ratio would mean the engine screaming at highway speeds.

Ok, sounds like 3.25 gears with Truetrac is the way to go!

Thanks for the help!
Kevin

The 3.25 ratio is for 9" only - with an 8" you get 3.20.

Thanks Royce, then the 8" goes from 3.20 to 3.40? Probably stay with 3.20 or is the 3.40 still a good combo? I am just trying to get that nice combination between street and highway although I rarely take it on the highway. Do you have an opinion on the Eaton Truetrac vs just a trac lock?

I only use Detroit Lockers because the clutches in anything else wear out quickly. I would stick to 3.20 the higher gears will be annoying in my opinion without an overdrive.

Thanks for the advise, much appreciated!

I’m just getting ready to pull my 8" which had 380:1 with true trac.
I will be selling the one year only Dura grip-Yukon. If interested?

Robert, Washinton state

What exactly are you wanting to sell? Are the 3.80 gear’s included

Just the complete dura grip assembly $100.00 plus shipping. Sorry no ring/pinion no center section.

Honestly, I blew the rear end out and converting to 9"-Strange Engineering rear end.

Robert

I have the Yukon version of a locker and 3.40 gears. I live in the northeast, not Texas, so I can easily live with the highway RPMs with a C4 (low-mid 3000s).

R.B.