Final drive gearing

[timbo2410]

Went from the standard 31's to 33's in the tyre department a while back and it's so much nicer on road and off .. only issue is, she aint that great on the old hills any more (and that's without a trailer) .. the 3.0 just hasnt got the legs .. is there a way of changing diff ratio to compensate ? or is it gearbox ratio?

[mudnut]

4.3 to 1, 4.1 to 1 and 3.9 to 1 diff ratios are commonly available.

[MB]

G’Evening Timbo Mate,
You definitely can change the ratios on your front and rear differentials (crown & pinion).
May I Nuffy suggest exploring here and elsewhere slight/minor and or extreme 3.0L engine modifications as a possible cheaper, less greasy/heavy first step.
It’s not a huge tyre rolling diameter change you’ve made and could be hopefully sorted out by squeezing a few little extra engine Killer Wasps out of Her [emoji120][emoji1696][emoji106][emoji106]


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[mihit]

Don't quote me, but I think some TD42s came out with a 4.8 diff which is what all the real mud sluts run.
4.1 (what I run, 33s, NA, TD42), 4.3 (??) and 4.6 (TD28) all common enough.

The 3.9 diffs were on petrol autos and...you don't want them.


But yes... probably more suitable to upgrade the donk. "slap a turbo on it"... or upgrade to the qd32, or td...

[mudnut]

Don't quote me, but I think some TD42s came out with a 4.8 diff which is what all the real mud sluts run.
4.1 (what I run, 33s, NA, TD42), 4.3 (??) and 4.6 (TD28) all common enough.

The 3.9 diffs were on petrol autos and...you don't want them.


But yes... probably more suitable to upgrade the donk. "slap a turbo on it"... or upgrade to the qd32, or td...

4.3 is for the RB30.

[MB]

………
..
The 3.9 diffs were on petrol autos and...you don't want them.


………..qd32td...

Apologies for quoting mihit Legend Mate [emoji120][emoji106][emoji106][emoji23]

Our old family ‘GU TD42T 2002 3.5T towing legal Manual’ variant Wagoooon did have them horrible highway 3.9’s too [emoji2961]

Rest assured Folks, sounds like New Zealand and certainly most of the Mountainous East Coast of Straya have almost eradicated them pesky 3.9’s, relocated actually over to Western Australia by PatrolApart, as its flat as a Shit-Carters hat [emoji145]……150kmph tail wind boat towing fishing fuel saving needs [emoji736][emoji23]


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[Hodge]

Rest assured Folks, sounds like New Zealand and certainly most of the Mountainous East Coast of Straya have almost eradicated them pesky 3.9’s,


"Almost" eradicated Marko mate. Lol
There's a set still getting me around the place..
Future plans to amend that ...

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[timbo2410]

I must admit a few more horses would be nice ..but .. I do miss a lower crawling speed as well. Especially on some of the rougher slower tracks around our neck of the woods.

[pollenface]

What's your vehicle? What year/engine/gearbox?

[Stropp]

Apologies for quoting mihit Legend Mate [emoji120][emoji106][emoji106][emoji23]

Our old family ‘GU TD42T 2002 3.5T towing legal Manual’ variant Wagoooon did have them horrible highway 3.9’s too [emoji2961]

Rest assured Folks, sounds like New Zealand and certainly most of the Mountainous East Coast of Straya have almost eradicated them pesky 3.9’s, relocated actually over to Western Australia by PatrolApart, as its flat as a Shit-Carters hat [emoji145]……150kmph tail wind boat towing fishing fuel saving needs [emoji736][emoji23]


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I still have 3.9 in WA but would change to 4.11, patrolapart send a lot to Brunswick diesels as they use them in their v8 conversions as most 3 LTR have 4.11 from my understanding

[PeeBee]

Something is not right with this conversation. The equation of Power relative to torque is P=2PiNT/60000 where power is P, Torque in Nm, N = rpm, Pi=3.1416. If you maintain the Power and change the rpm, the Torque is affected. I dont see how you can go from 31" to 33", be happy with the driveability and not realise the issue is the impact on the avail torque as you are probably sitting at a different spot on the torque curve. Swapping diff ratios is only going to land you back where you started - I think, as others have suggested, you look at the power component of the equation to get better driveability as the torque curve will change to compensate.

[mihit]

Something is not right with this conversation. The equation of Power relative to torque is P=2PiNT/60000 where power is P, Torque in Nm, N = rpm, Pi=3.1416. If you maintain the Power and change the rpm, the Torque is affected. I dont see how you can go from 31" to 33", be happy with the driveability and not realise the issue is the impact on the avail torque as you are probably sitting at a different spot on the torque curve. Swapping diff ratios is only going to land you back where you started - I think, as others have suggested, you look at the power component of the equation to get better driveability as the torque curve will change to compensate.

Yeah... TD42 has about eleventy billion torques so the 33s don't bother it much. I think it actually puts it in a much nicer driving range (for what I do).

Does push EGTs if you try hauling up hill at low revs...but it'll still do it though. :D

[timbo2410]

Soooo ... do I get from this conversation NOT to look at dif ratio and to go for higher horsepower?

[mihit]

Soooo ... do I get from this conversation NOT to look at dif ratio and to go for higher horsepower?

-Always- go for more horsepower :D

[pollenface]

Soooo ... do I get from this conversation NOT to look at dif ratio and to go for higher horsepower?

Personally, I would change diff ratios to match the tyres.

[timbo2410]

so what ratio would I need?

[nipagu7]

some 3 ltr's have 4.3's ( early di's , i think ) , most have 4.11's check your compliance plate on the firewall near the brake booster . i think it is listed as the trans axle code . if you put on 33's and you have 4.11 diffs , changing them to 4.3's will put you back to standard gearing . if you have 4.3'you will need to go to 4.6's to get back to your standard ratios .

[pollenface]

so what ratio would I need?

depends on your vehicle/engine/gearbox combination which I encourage you to share with us :)

[timbo2410]

I thought I had .. patrol wagon, 3 litre .. 5 speed manual