jesterarts/calais_304.
I've just completed a complete V6 engine, auto gearbox and diff rebuild to LSD.
The insight i can give with this experience is.....diff gears will give instant noticeable bang for your bucks.
On a completely stock car, including stock exhaust, the change of diff gears will most likely give more realistic increase in performance than say "cosmetic mods" like CAI, lifters, or even exhausts for that matter.
I was undecided for months of which gears to go 3.45 or 3.7.
I wanted to go 3.7 but decided to go 3.45 for a few reasons, my cam (crow cam stg 2) is not big enough to get the most out of the 3.7 gears, there was no 3.7 gears available when i was looking and since i do a fair bit of highway driving 3.45 is better with economy.
But a set of 3.45 was available for cheap from a mate, so 3.45 was decided.
Apparently, 3.45 and 3.9 are quite readily available but not 3.7, a set of new 3.7 i was quoted was around $600-$700.
I was quoted with everything new for $1800, diff gears, LSD and labour but it did not include speedo recalibration - being an independent diff, labour is more.
My diff just cost me $1175 - me supplying 3.45 gears $150, labour and new LSD supplied by the diff specialist $800 and an off-the-shelf speedo recalibration box $225.
It is better to go to a specialised diff mechanic, the general mechanic most like sends your diff to these guys anyway.
What i have just written is from the experience of research and talking to these specialists and i'm very happy with the instant increase in performance around town.
I have not taken it on the freeway yet to let you know what revs it does at 100 kays, the speedo correction box is not yet wired and at the moment it is about 10kays out - speedo says 70-72 but actually only doing 60.
As stock at 3.08 diff gears, it used to do 100 at 1750 revs, the autos have a very tall final drive which gives excellent fuel economy on highways.
I expect it to be around 2000 rpm, which will still be very good.
If you got a manual, in my opinion 3.45 will be ideal.
But, the best advice i can give you is shop around, talk to your mechanics and the diff specialists.
