I have an electronic speedo adjustor in my XR8.

its basically just a little box with 8 dipswitches in it. Its piss easy to setup and use. all you really need is a basic understanding of binary.

I got mine for free, so I am not sure how much they are. speak to mall wood - he organised mine (it came from a company in melb)

I dont have time slips on me, but I went from 13.9 down to 13.5 with a change of ratio from 3.08 to 3.7 (but keep in mind my torque curve will be a lot different to your inline 6's)

it isnt just that easy. guys with 25 spline EA diffs can use their housing to fit R31 gears(3.7, 3.89, 4.11) in but all you other guys EB (onwards like myself) have to get yourself an EA 3spd/25spline diff housing. then put the pinion (ie. 3.89) into it (the R31 stuff doesn't fit EB onwards housings). and your current 28 spline carrier and axels but stick the corresponding crownwheel onto it (ie. 3.89) and put the diff together. then your next problem is that EB onwards use fatter lower trailing arm bushes then EAs so you either need to:

1. get EA lower trailing arms and use shims at the front (washers or something)
2. get any e-series arms and have EB -> bushes pressed in one end and EA ones in the other (this will be more expensive)

then your diff will bolt straight into the car and give you have more pickup. i definately recomend this to anyone looking for a big increase in acceleration. this is pretty hard to do yourself though and i wouldn't recomend anyone try it at home unless they know a bit about diffs. also the diff's in R31s have a common problem: the upper trailing arm bushes wear and the diff rolls forward which wears the gear funny and causes them to make noise so its gonna be hard finding a a*** in good condition. i got my 3.89s for free and they are quite noisy (most of you guys would probably swoon at the thought that its my daily driver )

so in conclusion you can do it cheap like i did (free gears, $30 housing from u-pull-it, $15 trailing arms from u-pull-it and some oil) but my diff is very noisy however it works and it is fun

otherwise if your car isnt a hoon-mobile like mine then get a shop to do it for you and it'll be shimmed properly, quiet and hopefully have a long life. if you live in Adelaide then Boss Racing Differentials at Lonsdale are the people to see.

also you can buy a*** for the newer falcon diffs lie 3.73s but they cost about $300-$400 for the gears then you need them fitted (professionally) which will prolly cost about $1000

i got brand new 3.73 gears fitted with all new bearings for $1100

I paid for a 9" LSD packed with 4.11 for $1000 (or something close to that, it was a few years ago now)

hey dude id be lookin at somethin similair where bout did u get it done...was it in ACT ?

Cheers
Kev

Nar was in melbourne, at a mob called Preston Auto and Diff, ppl pay em out for being on the chap side, but I beat the crap outta mine and I think the LSD has only just paid out, so got a good 4 years outta it behind my 351, so for the price I think its good kit.

perfect example of some one who should not be working on cars

I was under the impression that R31 gears would fit. I didn't know there was a difference between crown and pinon wheels for the 25 and 28 spline centres.

not sure if this is entirely correct....there r 2 different sized crown and pinion gear setups (78 series and 75)...
EF/EL 3.08 housings r 75 and cannot accept 78 stuff without machining...
fairly sure everything else is 78 stuff which means compatable with R31

anyway ill be doing a diff gear swap on an EF 3.23 diff using 3.7 R31 gears shortly so ill let u know how I go