4.6 diff versus 4.3

[dom14]

Hey guys,

What is the advantage of 4.8, 4.6 ratio H233B rear diff over 4.3?

Mine is an RB30, carby, manual with stock 4.3 diff.
I got 235/85s atm, which comes to around 32".

So, is there any advantage for me for having a 4.6(or even 4.8) diff?!

Thanx
Cheers

[Stropp]

A lot less load on the motor but a lot more revs

[nissannewby]

A lot less load on the motor but a lot more revs

Basically this. Gearing is doing the work so quicker acceleration. But one step in ratio usually adds around 200rpm at cruise speeds etc.

[dom14]

So, if I go down on ratio and install 4.11 diff on mine, I would get sluggish take offs, but better fuel economy and less revving overall?

[liftlid]

So, if I go down on ratio and install 4.11 diff on mine, I would get sluggish take offs, but better fuel economy and less revving overall?
The car could be crap off road as well.

[Rock Trol]

So, if I go down on ratio and install 4.11 diff on mine, I would get sluggish take offs, but better fuel economy and less revving overall?

Not necessarily better fuel economy because if the engine is lugging it may use more fuel to keep the speed up. Or you need to give it more berries to make it go. Depends on how much torque you have low down.

[Throbbinhood]

I'm still running 4.3s with my 35's on my rb30.. Yeah, performance suffers a little, and the biggest downfall is probably downhill in low range first, it's still quite quick, fine for most thing but some of the steep downhill bits in the high country mean I'm clutching in and just letting the brakes inch me down... Fuel economy, I've gone up 1L/100km on 35's from 31's, so would take a while for me to recoup the cost of 4.6's, which are usually 1-2k depending on condition etc. For 32's, stick with the 4.3's.

[TheFlyingBadger]

Have a look at the calculator here (http://www.nissanpatrol.com.au/forums/showthread.php?34166-RPM-Gear-Transfer-Diff-Portal-gt-Speed-calculator)

It'll tell you what you can expect in terms of revs at a given speed

[dom14]

I'm still running 4.3s with my 35's on my rb30.. Yeah, performance suffers a little, and the biggest downfall is probably downhill in low range first, it's still quite quick, fine for most thing but some of the steep downhill bits in the high country mean I'm clutching in and just letting the brakes inch me down... Fuel economy, I've gone up 1L/100km on 35's from 31's, so would take a while for me to recoup the cost of 4.6's, which are usually 1-2k depending on condition etc. For 32's, stick with the 4.3's.

Are you saying fuel economy improved when you went from 31" to 35"?

[TheFlyingBadger]

Are you saying fuel economy improved when you went from 31" to 35"?


no, he went up 1l/100km with the 35s. Litres per 100km, low number is good, high number is a TD42TI on 35s and 3.9 diffs. :|

[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.

[liftlid]

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 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.
Sounds like he is saying the car runs on going down hill with the 35' rubber compared to the 31'

[Throbbinhood]

Sounds like he is saying the car runs on going down hill with the 35' rubber compared to the 31'

Pretty much this.. It's hard to explain, but take your car down a long steep hill and stop. put it in first and just let it roll down. You'll find you'll roll to a certain speed, and then generally the engine will start to hold the speed. In diesels, this is generally pretty low, in my rb30, this is generally 2500-3000rpm. This of course varies with how steep the hill is. Having 35's on as opposed to 31's means that the speed I am doing in this rev range is increased, and hence steep descent's on rough terrain can mean some brake/clutch work.

[dom14]

Pretty much this.. It's hard to explain, but take your car down a long steep hill and stop. put it in first and just let it roll down. You'll find you'll roll to a certain speed, and then generally the engine will start to hold the speed. In diesels, this is generally pretty low, in my rb30, this is generally 2500-3000rpm. This of course varies with how steep the hill is. Having 35's on as opposed to 31's means that the speed I am doing in this rev range is increased, and hence steep descent's on rough terrain can mean some brake/clutch work.

Yeah, I think I understand what you are trying to explain. You get less of an engine brake with 35" than with 31" on a given gear and steep angle down a hill. I think the reason is 35" goes further on the ground per turn of the wheel than 31", making the engine braking slightly less effective.

[dom14]

Sounds like he is saying the car runs on going down hill with the 35' rubber compared to the 31'

Yeah, I'm experiencing the same thing in a different degree when I switched from 225/75 R16 to 235/85 R16 for highway driving. So, I do understand it now. :)

[TheFlyingBadger]

Yeah, I think I understand what you are trying to explain. You get less of an engine brake with 35" than with 31" on a given gear and steep angle down a hill. I think the reason is 35" goes further on the ground per turn of the wheel than 31", making the engine braking slightly less effective.


Correct..

RB30, 1st Gear, Std Low Range @ 2500rpm




Diff Ratio
Tire Size
Speed (km/h)


4.375
31
12.63


4.375
35
14.26


4.625
31
11.95


4.625
35
13.49


4.880
31
11.32


4.880
35
12.79


5.130
31
10.77


5.130
35
12.16




RB30, 1st Gear, 43% Reduction Low Range @ 2500rpm



Diff Ratio
Tire Size
Speed (km/h)


4.375
31
8.92


4.375
35
10.07


4.625
31
8.44


4.625
35
9.53


4.880
31
8.00


4.880
35
9.03


5.130
31
7.61


5.130
35
8.59

[Throbbinhood]

Engine braking sucks in an rb30 anyway. Bolt the 35's on, and go from there ;)

[the evil twin]

35's mean you will notice decreased perfromance with your braking as well.

Larger tyres mean a greater pedal effort for the same amount of deceleration.

[dom14]

Engine braking sucks in an rb30 anyway. Bolt the 35's on, and go from there ;)

It wasn't that bad with 225/75 R16(29 inch diameter), but of course 29" is way too small for a GQ. :)

[dom14]

35's mean you will notice decreased perfromance with your braking as well.

Larger tyres mean a greater pedal effort for the same amount of deceleration.

Absolutely! I'm already experiencing that with by switching from 29" to 32" tyres.
I originally thought, 'cos larger diameter tyres get a slightly more grip from slight increase on tyre to road grip surface area, so better braking.
But, that's not the case.