I am considering a diff ratio change from standard (3.45:1) to a 3.9:1. Has anyone done this conversion I need so info? What revs to you do along the highway at 100 in fourth? Does it affect your fuel economy much?

yes it will affect fuel usage, 3.9 is a good ratio for an auto or 5 speed manual. If you have a auto it will bring the rev's up considerably, and whack your speedo out. I went 3.08 > 3.45 in me old car (VL V8 auto), wished I went 3.9 in the end as it was only driven on weekends. If you dont drive car everywhere, go 4.11 for the better 1/4 mile times and races Some original photos have not been recovered yet.

mines an auto rb30e and its a daily driver and I drive approx 72 klms a day getting to and from work in the 100 zone. If the revs don't jump by much on the highway I'll go for it but otherwise I might hold off until I move towns.

i went from 3.45's to 3.89's - revs did jump up a bit cruising down the highway, but nothing rediculous. i think it sat on 2400 rpm instead of 2100 rpm... obviously fuel economy is effected as your motor is doing more revs to cover the same distance.. but it picks up off the line alot better then the 3.45's.

Awesome I was expecting like around 3000 rpm... I can live with 2400rpm thats stuff all of a jump. not that I don't doubt what you say InsaneVL but has anyone else done this, I need this confirmed?

Yep, i've got a auto VLT, did the ratio change to 3.9's, and it's fine on the highway... InsaneVL's right with the revs... not a major change, but off the line! heheh heaps better! I didn't notice a rise in fuel usage at all with mine. Go for it :P

kewl thanks guys. Looks like I will go ahead with the swap over. ) Some original photos have not been recovered yet.

also jumped up to 3.7's. Can't notice the rev increase much, but can feel pick up down low more

This is all great for quick take offs, but who has any problems with keeping traction when taking off from the line? Does anyone have the answer? With the 3.45's I've got now, I find it hard to keep traction and my car is reasonably stock. What if the Vlt was mildly worked? I'm looking at going the same diff ratio conversion in the future but if all I'm going to achieve is fried rears, then i can't justify it.

Could any one give me some help on this. Is this mod hard to do? how expensive is it? and where would i get the parts? thankgs guys

I just went to the local diff shop, I wouldn't try screwing with a diff unless you had someone to help you who knew what they were doing. I'm getting my axels replaced and my center as I currently have 25 spline axels and I want 28 spline. Mine was going to cost a bit as all the parts were new and becaseu of the labour involved, so it was around $1500. If you've got a drum brake rear end the best thing to do would find a set of vlt axels and bolt them up - you could do it yourself its pretty easy. Second hand non standard diff centers are hard to come by, but if you found some it might save you some money.

r31 skylines will be good source for parts..manuals have 28 spline disk brake 4 pinion 3.7's and autos have 3.9's pickem up cheap too

yeah I had a look into that but thye axels were too short and the center wouldn't just fit straight in as the housing needed some attention to make it fit. Atleast by fitting brand new parts I get piece of mind knowing that theres atleast a few kms in the diff before something can go wrong, well thats the way I look at it.

so what has/did it cost to convert a 3.45 vlt lsd diff into a 3.9 lsd diff? key word being lsd, and not single/spooled.

well it was going to cost me 1500 for new axles and a new center of course which is lsd 28 spline. For the center alone (ie already got 28 spline axles) was 700 plus install which I think was around 300 bucks.

Quote: Originally Posted by Sleek This is all great for quick take offs, but who has any problems with keeping traction when taking off from the line? Does anyone have the answer? With the 3.45's I've got now, I find it hard to keep traction and my car is reasonably stock. What if the Vlt was mildly worked? I'm looking at going the same diff ratio conversion in the future but if all I'm going to achieve is fried rears, then i can't justify it. I think that it wont affect traction, might even improve, esp if auto, long gears dont do a lot for traction, short gears can allow you to get off the line more cleanly if you know what I mean