3.9 diff gears for XR8 ute.

[XR8 Uterous]

I'm interested in changing the diff ratio in my ute, got a couple quick questions...

1) What are people paying for this both parts and installed?
2) Does it effect the speedo a great deal, if so, how was it fixed?
3) Effect on fuel economy (I didnt buy a v8 to be good on fuel, but the effects would be good to know)
4)Would 3.9s be the go behind a T5, or something else recommended?

Cheers

[b2tf]

Yo

got a mate who's put them into his and it's a stick too so I will ask him and get some answers. I think the overall reaction was positive.

[KR1STO]

A mate of mine put them in..
Answers to your q's..
1. About $800 I think he paid, included tightening LSD. (live axle)
2. Speedo was out.. Can get a speedo corrector from Jaycar, or try and figure out how many teeth you need on the gear on the transducer..
3. Unsure.. Would mean you're revving a little higher on highways..
4. My mate was pleased with 3.9's, but, has said if he had to do it again he'd go 3.7's.. seems to think 3.9's are more for an auto.. Only need 3.7's with a T5..

Hope that helps mate!

[The Monty]

1. To put just diff gears in, and nothing else, should be around the $300-$500 mark.
2. Speedo will be out, get someone you know to sit beside you at 100kmh. Write down what your speedo says, for eg: Mine says 130km. So its out 30%. So at 60, mine will read 78, 70 it will read 91, 80 - 104, etc etc.
3. I use more fuel with my 3.08's then 3.9's, mostly highway driving.
4. Best mod I have ever done, although its in an auto. Have been in a manual with 3.9's, does rev a little higher, first gear isnt much use, but overall it was really good.

[DW260]

Originally Posted by b2tf

Yo

got a mate who's put them into his and it's a stick too so I will ask him and get some answers. I think the overall reaction was positive.

I assume you're talking about me?

1. Cost $1480, which was new gears bearings and LSD. Everything.

2. I have to sit on about 130kph to do 110 actual speed. Verified by a GPS. No fixes that I could be bothered with. Just do the math and add 15%.

3. No difference to fuel consumption that I've noticed.

4. Would I do it again? No. With an auto? possibly. Manual, I would put my money towards something else.

[DW260]

I should also add that overtaking performance has improved dramatically. But don't do it if you're under the impression it's going to totally transform the performance and turn it into jet.

I think you would be far better off putting your money towards some AFR's or similar.

Most noticeable modification I did was install the manifold spacer.