4.6 diff versus 4.3

[Throbbinhood]

As above, went from 15-16L/100kms on 31's, to 16-17L/100kms on 35's (3" lift, winch, barwork, lights went in at same time so I'm fine with the increase).

[dom14]

Have any of you guys used a 4.8 diff?
Is it any use(for 35" muddies), etc?

[Stropp]

I have 4.3 with 35's and find it pretty good, I know of others that have 4.6 and swear by them but we have 4.2 tdti engines, not sure on a 2.8

[dom14]

I have 4.3 with 35's and find it pretty good, I know of others that have 4.6 and swear by them but we have 4.2 tdti engines, not sure on a 2.8

Mine's an RB30, so the gearbox is different. I'm guessing 4.3 is probably enough for TB and TDs with their bigger transmission, but may not be the case for smaller RB30 transmission?

[Throbbinhood]

What is the end result you are chasing Dom? Are you upgrading Tyre sizes?

[dom14]

What is the end result you are chasing Dom? Are you upgrading Tyre sizes?

To find out for sure whether there are any side effects of using 35" etc on a standard 4.3 diff, and if there's any advantage of using a 4.6 or 4.8 diff with 35", etc tyres.

[Throbbinhood]

Ok. All this on 35's.

4.3 Slower acceleration, longer gearing, slight increase in fuel consumption. 5th gear doesn't get used too often unless I've got a long straight, otherwise sitting in 4th is more economical @ 100 on 35's. It's been fine for what I use it for, only thing that sort of sucks is steep downhills, low first is too long, but tbh I think it would still be too long on 4.6/4.8, probably want reduction gearing for the really steep downhill.

4.6 will help bring the gearing back into line with stock. Your fuel economy may come back a bit compared to 4.3's, but 35's will increase it anyway (rolling resistance, weight, friction etc).

4.8 will shorten the gearing, so you'll need more rpm's. You'll have better response, but may come at the expense of higher cruising rpm's.

[dom14]

Ok. All this on 35's.

4.3 Slower acceleration, longer gearing, slight increase in fuel consumption. 5th gear doesn't get used too often unless I've got a long straight, otherwise sitting in 4th is more economical @ 100 on 35's. It's been fine for what I use it for, only thing that sort of sucks is steep downhills, low first is too long, but tbh I think it would still be too long on 4.6/4.8, probably want reduction gearing for the really steep downhill.

4.6 will help bring the gearing back into line with stock. Your fuel economy may come back a bit compared to 4.3's, but 35's will increase it anyway (rolling resistance, weight, friction etc).

4.8 will shorten the gearing, so you'll need more rpm's. You'll have better response, but may come at the expense of higher cruising rpm's.

Thankx Chris.
What is the exact issue with 35" going down the hill with 4.3 diff?
What do you experience when going downhill?!
4.8 is an aftermarket ring and pinion combination. Not from Japan I think. From Italy from what I read on the internet and apparently harder to set the backlash properly.
Without having both front and back diffs, ratio change is useless anyway, isn't it?
Mine's got enough lift by the looks of it. I reckon I can squeeze in 35"s without much issues when I get hold of a set of wheels.

[Throbbinhood]

Thankx Chris.
What is the exact issue with 35" going down the hill with 4.3 diff?
What do you experience when going downhill?!
4.8 is an aftermarket ring and pinion combination. Not from Japan I think. From Italy from what I read on the internet and apparently harder to set the backlash properly.
Without having both front and back diffs, ratio change is useless anyway, isn't it?
Mine's got enough lift by the looks of it. I reckon I can squeeze in 35"s without much issues when I get hold of a set of wheels.

You just don't get the engine braking (being an rb30, not much anyway). My car for instance, I don't get that backpressure/engine braking until 2.5/3k rpm. Those rpm on 35's compared to 31's is significantly faster. 4.6's may bring that back into line, but to be honest, might still be too quick anyway.. It hasn't been a big problem, more an annoyance...

I'm not 100% sure, maybe someone else can clarify, but didn't 2.8GU come with 4.8 diff gears? If so, couldn't you just transfer the centre?
Yes both front and rear diff needs to be the same ratio.

How much lift do you have?

[dom14]

You just don't get the engine braking (being an rb30, not much anyway). My car for instance, I don't get that backpressure/engine braking until 2.5/3k rpm. Those rpm on 35's compared to 31's is significantly faster. 4.6's may bring that back into line, but to be honest, might still be too quick anyway.. It hasn't been a big problem, more an annoyance...

I'm not 100% sure, maybe someone else can clarify, but didn't 2.8GU come with 4.8 diff gears? If so, couldn't you just transfer the centre?
Yes both front and rear diff needs to be the same ratio.

How much lift do you have?

2.8GU came with 4.6 diff(and some may be 4.3)
4.8 crown wheel and pinion is an after market Italian import, according to the internet.
Yes, AFAIK, 2.8GU diff is H233B, which is a straight swap for GQs.

I'm not sure the exact amount of lift on mine.
I have to take a guess and can say it's above 2".

You get the engine braking by switching from higher to a lower gear than suitable for particular speed and revs go high as a result, while car slows down. I'm not sure what you meant by engine braking not happening until 2500/3000rpm.