patrol diff ratios

Submitted: Wednesday, May 09, 2012 at 20:39
ThreadID: 95463 Views:4618 Replies:7 FollowUps:8
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hi all have a 99 mod 4.2td Nissan ute i wish to get higher speed on the highway without lifting the revs, at 100k the revs are at 2300rpm in 5th gear now i wish to try and get those revs down, say 110k per hour for 2000rpms. is this possible and how do i do it, can anyone help.
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Reply By: Ross M - Wednesday, May 09, 2012 at 21:07

Wednesday, May 09, 2012 at 21:07
G'day Mick'n'Jen
If you want to gear it to be 2000rpm, it is a factor or about 8% at 100kmh.
This can be done two ways, by either altering the diff ratios of both diffs and is quite expensive unless you know where to get some replacement lower ratio/higher output speed diffs or gear sets.

The other way is to fit larger tyres. Many people do this and depending on what size tyres you already have some increase "may" be beneficial.
After you pass the torque versus load aspect of the vehicles ability you will experience increased fuel consumption as the engine is now trying to drive the same load but with a overall engine to road ratio equivalent to 6th or 7th gear, again depending on the initial and final tyre sizes.

Best to test the tyre option by borrowing a friends bigger wheels to find if it is suitable for your needs.

Seeing you want to up the speed and also reduce the revs a significant amount I would think it won't be economical to go past the halfway mark of your expectations. Possibly around 2100 at 100kph before you start to go out of whack with the load/speed.

Ross M
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Follow Up By: Cravenhaven - Wednesday, May 09, 2012 at 21:16

Wednesday, May 09, 2012 at 21:16
I was just doing some calculations before posting but you beat me to the punch. However I did work out that if Mick/Jen are running standard tyres which I think are 265/70/16 then they would have to go up to a 33" tyre=285/75/16 to drop the revs to a bit over 2100. To get to 2000 rpm at 110km/hr you would need 35" tyres which are huge.
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Reply By: Michael ( Moss Vale NSW) - Wednesday, May 09, 2012 at 21:15

Wednesday, May 09, 2012 at 21:15
Mick! Have a look on the Patrol 4x4 forum, there is a lot of info on this. I think the ute has a bigger, heavy duty diff carrier and housing so the ratios may be limited due to this. There are many guys on patrol forum that would swap carrier and or housings so they can use there vehicles for chewing through the scrub or whatever they do. Check the forum, they know more than me about this!!! Michael
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Reply By: GT Campers - Wednesday, May 09, 2012 at 21:22

Wednesday, May 09, 2012 at 21:22
Why do you want to get the revs down? As has been said, the easiest way is through minor tyre size change (with a speedo re-cal). But you will use more fuel and really blunt performance, especially when loaded, with 'step-off' around town and with off-road
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Reply By: Member - Ed C (QLD) - Wednesday, May 09, 2012 at 21:29

Wednesday, May 09, 2012 at 21:29
IMO, the most effective way to do this would be to simply change the 5th gear ratio..

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Follow Up By: Cravenhaven - Wednesday, May 09, 2012 at 21:51

Wednesday, May 09, 2012 at 21:51
And it just occurred to me that a lot of the earlier Nissans had a problem with the 5th gear splines. Apparently they did not engage fully so are a common failure, particularly when towing in 5th gear. The Marks adapter upgrade solves that problem as well as decreasing your drive ratio.
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Follow Up By: GT Campers - Thursday, May 10, 2012 at 11:47

Thursday, May 10, 2012 at 11:47
yep that was/is a problem - the fifth gearset was made wider for replacement (and I think for production); of course the splines' engagement is subsequently wider too. In general, fifth gear is the weakest cog in any box and shouldn't be used for towing
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Follow Up By: Kumunara (NT) - Friday, May 11, 2012 at 09:51

Friday, May 11, 2012 at 09:51
The fifth gear problem on the patrol was an error in manufacture of the spline. The splines were too short. That was way back in 200 and has been rectified long ago.

The patrol has a strong gearbox that has a fifth gear capable of towing. In most vehicles the fifth gear is not suitable for towing.
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Follow Up By: Cravenhaven - Friday, May 11, 2012 at 11:07

Friday, May 11, 2012 at 11:07
But the Patrol in question is a 99 model so would be subject to this problem, unless it has been fixed since. I was mentioning it in case the OP may not know of this problem and it could make the Marks adapter solution look more palatable.
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Reply By: gq89 - Thursday, May 10, 2012 at 08:22

Thursday, May 10, 2012 at 08:22
bear in mind that the engine produces optimum torque at around 2500, so you probably do not want to drift too far away. That said i run 33s on a GQ ute and sit around 2150 at 100. The additional tyre size/weight is noticeable and will add about 10% to your fuel economy (to your detriment).
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Follow Up By: mikehzz - Saturday, May 12, 2012 at 19:09

Saturday, May 12, 2012 at 19:09
Are you sure you are using more fuel because your odometer will be reading low with bigger tyres. It makes it hard to know your real fuel economy. I've checked mine with only slightly bigger tyres and on a 5 km freeway test strip mine is reading 4.7 kms now. Therefore when my odometer says I have done 470 kms I have really done 500 kms. That makes it appear I am using more fuel. Helps keep the real kms down on the car though :-)
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Follow Up By: gq89 - Monday, May 14, 2012 at 07:49

Monday, May 14, 2012 at 07:49
despite the change in odometer, bigger tyres mean more weight distributed further away from the axle centre, so are heavier to turn. going from 31 to 33 will cost about 8% loss in fuel economy, you do get the benefit of higher ground clearance.

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Reply By: The Bantam - Thursday, May 10, 2012 at 09:16

Thursday, May 10, 2012 at 09:16
I've seen a few people talking about changing the highway revs on big 4wds of late.

It seem to me thay don't get it.

This is not a light pasenger car that has plenty of surplus power and is light incomparison to the engine capacity and at 100KPH is traveling at well below (like 1/2 or 2/3) its capable road speed.

Ya patroll is over 2 tonnes unloaded, proabably over 3 tonnes fully loaded, its a big lump of a thing and is pushing a lot of air in front of it.

The engine and gearing will be designed to keep the engine on the peak of its torque curve, at highway speeds, this is where it produce the best highway fuel economy.

This is particularly so of diesel engines.

There is no way arround the fact that the big nissan chews the juce, if ya try and drive it like a pasenger car on the highway it will get expensive.

Get used traveling a bit slower and not being the fastest thing on the road.

cheers
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Follow Up By: GT Campers - Thursday, May 10, 2012 at 11:26

Thursday, May 10, 2012 at 11:26
yep bantam you are right in general, also many EFI/managed cars have a lean cruise strategy at around 100-110km/h and this gets all messed up with changes away from standard gearing
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Reply By: Rockape - Saturday, May 12, 2012 at 20:02

Saturday, May 12, 2012 at 20:02
Hi Mick'n'Jen,

Please just have a thing about this. You are driving one of the best 4wd's made and that comes from a Tojo owner.

When Mister Nissan (JAPAN) made that vehicle they matched the engine to the best engine life and the best fuel economy. The old 94 engine was even better.

Here is an example. I run big tyres and the reason for this is 2 fold. I tow a lot and have to use 4th gear because my gearbox can't handle the load on 5th gear . This causes a problem with engine revs, so the big tyres. I can get away with this because the engine I have develops heaps of torque.

Now for the other reason. My engine develops max torque at around 1800 rpm, but my best fuel consumption is between 2200 and 2300 revs. With the bigger tyres I balance noise, fuel consumption and acceleration and I do get great fuel consumption out of the old clunker.

Hope this helps.





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