D40 Diffs ratios.

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TigerST

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Ok guys. Is the any different in diff raitos between the YD25 and VX90.

I was reversing with an empty car trailer into my driveway to get in the back yard. it not a steep drive way but I dont have a low enough raito do it with out applying power, making the trailer play games. In Low no worries but I dont like doing that as i have high traction drive way........
 
Wow, that's quite a difference.

I'm reading the official specs for the range and it's astounding.

The 4-cyl auto has a reverse ratio of 2.613:1 and a final drive ratio of 3.538:1.

The 6-cyl auto has a reverse ratio of 4.041:1 and a final drive ratio of 3.133:1.

Bit of a difference!
 
So I'm guessing a diff swap wont help my problem if anything cause more problems with other gearing.
 
I doubt I'd be trying to fit the front diff from a YD25-powered car into a V9X anyway, it's a little on the small side even for the YD25. Put the YD25 diff with a locker in and you stand a chance of keeping it going, but there's a considerable amount of extra torque in the V9X that translates directly to more little broken pieces up front. The rear diff will probably be fine.

This is the only problem with front hubs that can't be manually engaged/disengaged.

If you changed to a YD25 diff ratio you'd also change the highway dynamics, increasing fuel consumption. Part of the economy is from the low revs at cruise (1700rpm compared to the YD25's 2000rpm). That means less fuel per minute for the same distance travelled. Because the V9X is a larger capacity engine with more cylinders, revving it at the same level might use slightly less fuel per combustion stroke but with more combustion strokes, I'm wagering that you'd come out significantly worse than you are now with the ratio change.

Not to mention that your cruise speed will also be completely beyond the engine's comfort zone, up past the peak torque area into the "I'm burning gobs more fuel for a little less gain" area.
 
Sorry Should have said I own a yd25 and was thinking the V6 may have a lower ratio to bring out that power. So it would putt along nicely in reverse. The problem I'm facing with the YD25 is in reverse there is nothing before the turbo then to much.
 
Unfortunately going the other way - V9X diffs into YD25 - would be even worse, because the turbo wouldn't come on to cruise boost levels until 111km/h (I made a spreadsheet that works out the speed you'd travel at with a given gear ratio, diff ratio and engine speed). That's about 15km/h above its normal point and it might struggle rather badly - I'm betting its fuel consumption would be terrible!
 
Hey Lads,

There are now 4.1 ratios available for both the front and rear to suit D40 diffs, these have become available through 4x4parts.com, they became available this week.

4.1 ring and pinion for R180A front axle @ $495 USD
Link - https://www.4x4parts.com/nissan/41-front-ring-pinion-p-6938.html

4.10 Ring & Pinion for D44 rear axle @ $395 USD
https://www.4x4parts.com/nissan/410-frontier-rear-ring-pinion-p-6757.html

Master install kits and flanges are also available from these guys.

We have been waiting on these new ratio's for quite some time to allow a re-gear for those running larger tyres.

I'll start a new thread on this to gauge interest for use to bring some in and keep them in stock, or potentially run a group buy or somethign along those lines to get these diff ratios out to guys who want them at the right price.

New thread here - http://www.navara.asia/showthread.php?p=297106#post297106


Cheers,
Matt
 
Last edited:
With a 4.1:1 diff and 265/75R16 tyres (2.525m circumference) cruise speed is altered from 94km/h to 89km/h (instead of the 99km/h that those tyres would produce). This would lead to savings in fuel (less strain turning the wheels over). Not a bad thing if you're going to stay on larger tyres.

Even better - if you use 285/70R16s your cruise adjusts from 94km/h (standard 255/70R16 cruising at 2,000rpm) to 92km/h. Makes this diff PERFECT if you go the larger tyre.

If you use 285/85R16 tyres your cruise (@2,000rpm) should be 109km/h - and this diff brings cruise back to 99km/h.

I'd recommend the diffs to anyone wanting those tyres.

Note: it's important to consider the YD25 at 2,000rpm because that's the point where your (stock) engine is producing the most amount of torque (for maintaining speed) for the least amount of fuel. Any lower RPM and the torque falls away, any higher and the fuel input rises faster than the torque, making it not worthwhile.

In the V9X, that's 1700rpm.

Here's the formula if you want to whack it in a spreadsheet and do it yourself:

60 times cruise RPM times tyre circumference in metres divided by (top gear ratio times diff ratio) divided by 1000.

Tyre circumference is 3.141 times (2 times tyre width times profile divided by 100 PLUS rim size times 25.4) - then divide this result by 1,000 (convert from mm to m).

Examples:

255/70R16 has circumference of 3.141*(2*255*70/100 + 16*25.4)/1000 = 2.397m
285/85R16 has circumference of 3.141*(2*285*80/100 + 16*25.4)/1000 = 2.798m
 
Hey Lads,

There are now 4.1 ratios available for both the front and rear to suit D40 diffs, these have become available through 4x4parts.com, they became available this week.

4.1 ring and pinion for R180A front axle @ $495 USD
Link - https://www.4x4parts.com/nissan/41-front-ring-pinion-p-6938.html

4.10 Ring & Pinion for D44 rear axle @ $395 USD
https://www.4x4parts.com/nissan/410-frontier-rear-ring-pinion-p-6757.html

Master install kits and flanges are also available from these guys.

We have been waiting on these new ratio's for quite some time to allow a re-gear for those running larger tyres.

I'll start a new thread on this to gauge interest for use to bring some in and keep them in stock, or potentially run a group buy or somethign along those lines to get these diff ratios out to guys who want them at the right price.

New thread here - http://www.navara.asia/showthread.php?p=297106#post297106


Cheers,
Matt

So how would this help with towing and such.

With a 4.1:1 diff and 265/75R16 tyres (2.525m circumference) cruise speed is altered from 94km/h to 89km/h (instead of the 99km/h that those tyres would produce). This would lead to savings in fuel (less strain turning the wheels over). Not a bad thing if you're going to stay on larger tyres.

Even better - if you use 285/70R16s your cruise adjusts from 94km/h (standard 255/70R16 cruising at 2,000rpm) to 92km/h. Makes this diff PERFECT if you go the larger tyre.

If you use 285/85R16 tyres your cruise (@2,000rpm) should be 109km/h - and this diff brings cruise back to 99km/h.

I'd recommend the diffs to anyone wanting those tyres.

Note: it's important to consider the YD25 at 2,000rpm because that's the point where your (stock) engine is producing the most amount of torque (for maintaining speed) for the least amount of fuel. Any lower RPM and the torque falls away, any higher and the fuel input rises faster than the torque, making it not worthwhile.

In the V9X, that's 1700rpm.

Here's the formula if you want to whack it in a spreadsheet and do it yourself:

60 times cruise RPM times tyre circumference in metres divided by (top gear ratio times diff ratio) divided by 1000.

Tyre circumference is 3.141 times (2 times tyre width times profile divided by 100 PLUS rim size times 25.4) - then divide this result by 1,000 (convert from mm to m).

Examples:

255/70R16 has circumference of 3.141*(2*255*70/100 + 16*25.4)/1000 = 2.397m
285/85R16 has circumference of 3.141*(2*285*80/100 + 16*25.4)/1000 = 2.798m

Old Tony. Would this be worth it with the stock size or really only with 265
 
With stock tyre sizes you'd lose cruise speed at cruise RPM. You ought to marginally gain economy, because the effort required to push the car through the air at 95km/h is quite large, so reducing the speed (by moving the most efficient point of the RPM curve downwards) will have some benefits.

Also, hill starts will be better. Your overall gear ratio will be lower. Give me your tyre size and I'll plug the figures in.
 
255/65R17 tyres have a circumference 3mm less than the 255/70R16s on my car, so they'd be identical, so consider yours "stock". Your top gear ratio is 0.834:1 (0.827:1 on mine), the difference probably an allowance for the extra ponies. There's also a chance your cruise point is slightly lower (eg 1900rpm) but for the purpose of this exercise I left it at 2000rpm.

On stock tyres your 2000rpm cruise speed should be 97.4km/h (that's the slight variation in top gear ratio showing there exactly as expected).

Change the diff to a 4.1:1 and your 2000rpm cruise speed drops to 84km/h (your diff is currently 3.538:1).

If you did it, you'd think your car had a whole bunch of extra beans added - but she'd feel like she's running harder than she should when trying to keep up at freeway speed.
 
Big Drop wonder if it be worth it. Seen living in canberra I do 80-100 daily...

On The hume on the way to Sydney now and then I only do 100-105. Just nicer to sit at that speed in the Navara
 
I remember a few years back a guy install a swich on lux to do just that. If it could be down then I'm sure someone would have by now. With diffs that low you'll amost need an extra gear.
 
I remember a few years back a guy install a swich on lux to do just that. If it could be down then I'm sure someone would have by now. With diffs that low you'll amost need an extra gear.

I'll have a squiz, I had a momentary glance at it once before and didn't think our transfers were capable of it. I'll take a better look at it.
 
I'll have a squiz, I had a momentary glance at it once before and didn't think our transfers were capable of it. I'll take a better look at it.

I hope it is.
I'd love the 2wd low range. 1 thing I miss from my old Disco-1 the ability to use low with out the central diff locked.
 
4.1's wouldnt be much use unless your running 35's, i have 33's on mine and when towing in 5th (drive gear) it's reving 2500rpm at 100'ks push it more and it drink's too much juice. and mine is a manual
 
4.1's wouldnt be much use unless your running 35's, i have 33's on mine and when towing in 5th (drive gear) it's reving 2500rpm at 100'ks push it more and it drink's too much juice. and mine is a manual

Yeah Thats why we are talking about a way of tricking the system to us Low 2wd. Would solves problems in when you need that power and control with out the Pegion
 

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