3.9 diff gears in 5.0 manual?

[MrEL]

Hi all
Gettingmy diff rebuilt tomorrow after it went boom and I have a set of 3.9 diff gears here that I can have put in.
Putting 0575 gears in an 0578 case will cause some issues but is nothingmy diff guy cant work with.
Im just after peoples real world experiences.
Car is a 5.0 manual ute with factory 3.45.
So the guys who have done it.
Did you get a noticeable performance increase?
Does it revs its norks off on the freeway and use heaps of juice?
Is it worth doing?
Cheers

[BOTTLEDUP]

Got 3.9s in my 5.0 200kw TE50. I'm very happy with them 1st isn't too short to be unusable, and 5th on the freeway @ 100km/h the tacho is sitting on 2550-2600rpm. I can live with that.

Mid 'speed' acceleration (40-120km/h) is a lot better in all gears, especially 3rd & 4th. Any future engine mods will further enhance the performance.

[bartsau]

Got the T5 with a set of 3.9's and as good as they are I am thinking of going and trying some 3.7's. Find it sits on approx 2450 at 100km/hr.

1st is useable but very short I would prefer not quite so short. Having said that it is very forgiveable when launching at the drags with this setup. Doesn't ever really 'bog' down much at all.

As for fuel honestly not too big a difference at highway speeds. And the rest of the time it purely depends on how you drive it. I can be in 5th at 45km/hr if I want...

[MrEL]

Sounding like a winner all in all.
Im running 19's like Bart so to hear the overall experience with them is really good thanks.
Myself I would prefer to be doing the 3.7s as well , but a good mate dropped around a set of 3.9's tonight and handed them to me. Cant argue with the price there.
Just depends now on how they check out and how much extra the diff place is going to charge to shim them up. The rest of the remove and replace has to happen anyway regardless.

[BOTTLEDUP]

Honestly I don't know if there is enough of a difference between 3.45s and 3.7s to warrant the change.