is 3.9 diff gears too much?

AGRO-V8 · #1 24-10-2007, 04:43 AM

my current diff is the standard 3.08 gears, how big of a difference is goin to 3.9? will my top end be a hell of a lot different?
i know my take off will be better

and is their anythin i need to know about changing diff gears?

Morton · #2 24-10-2007, 07:52 AM

Yeah, first off, your speedo will be out. You'll have to get it recalibrated - less than a hundred dollars to get it done properly.

Also, you'll effectively shorten every one of your gear ratios, so in top gear on the freeway, you'll be cruising a few hundred rpm higher.

Example: I'm going from 3.08s to 3.73s. I usually ride at 1900rpm on the freeway at 100kph - after the change I'll be doing 2300rpm on the freeway at 100kph.

AGRO-V8 · #3 26-10-2007, 04:33 AM

Quote:

Originally Posted by Morton

Yeah, first off, your speedo will be out. You'll have to get it recalibrated - less than a hundred dollars to get it done properly.

Also, you'll effectively shorten every one of your gear ratios, so in top gear on the freeway, you'll be cruising a few hundred rpm higher.

Example: I'm going from 3.08s to 3.73s. I usually ride at 1900rpm on the freeway at 100kph - after the change I'll be doing 2300rpm on the freeway at 100kph.

cool thanks for that. well im tryin to get the best of both worlds, personally i wouldnt want it more than 2200rpm at 100ks on the freeway, yet i want that punch off the mark.
dont want to loose alot of the driveability

immortality · #4 26-10-2007, 05:56 AM

not sure what the overdrive ratio for the auto trans is but for a manual with 17" wheels and a manual trans (for V6 ratios, 0.72 overdrive ratio)

3.08 = 98.4km/h @ 1800rpm
3.45 = 97.6km/h @ 2000rpm
3.73 = 99.3km/h @ 2200rpm
3.93 = 99.3km/h @ 2300rpm

that should give you some idea of the change with each ratio

nsladden · #5 28-10-2007, 08:57 AM

I know someone who has a XP Falcon ute with factory 4.11 diff ratio. She wont go over 85-90km/h. Thats at revving at like 4500rpm.

-SV6- · #6 28-10-2007, 10:17 AM

Go the 3.9's you won't regret it. i was going to put 3.7 in my VN SS. I got 3.9 by accident so i got them put in. they weren't to bad. Awesome takeoff

beefcream · #7 09-11-2007, 03:38 PM

how much difference will the take ofs be? is it a absolutly massive change or just like meh its quicker