Diff gear ratios

[SSbeast]

I've got a VX SS 4spd auto. I've done a couple mods of full exhaust and cold air induction. Before i get a tune i want to put in some new ratio diff gears. I was talking to my mate another car nut and he said to put in 3.80 ratio. I still want to use if for highway use so around 140km/hr and have it not rev to high. But id still like to have good accelration from the mark. Any ideas? Cheers

[immortality]

from memory the auto's came with 3.07:1 (approx 1800rpm@100km/h) gears from the factory so stepping that up to 3.46:1 (factory ratio for cars fitted with the T56 manual trans) will see a slightly quicker take off and a increase of about 200rpm@100km/h. your next oprion would be to step upto 3.7's again quicker acceleration but add another 200rpm@100km/h. after that is 3.9's (as fitted to the HSV GTS models i believe) quiker again and add another 100rpm@100km/h (all these speeds@ rpm are approximated but fairly average)

i went from 3.08 to 3.45 in my V6 and haven't noticed areal increase in fuel usage. if you get a decent tune done it should be sweet