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1.4 Defender Transfer box v 1.2 Discovery 1 Transfer box "Phenomen

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Now this has bugged me for a while and I've found 2 minutes to finally get my coalesced thoughts down on paper...

You often get topics for people asking about how to improve the on-road abilities of the Defender - meaning wanting to increase fuel economy... reduce noise... increase speed etc ect. Amongst the options are installing an overdrive, putting bigger diameter tyres on, changing your diff ratio's and finally the changing of the transfer box ratio...

Now what really baffles me is that you get people whom have done the 1.4 to the 1.2 ratio box swap on defender I think mainly, then they usually complain that the gears feel too tall for the engine revs and people have trouble towing and all sorts of other complaints...

Now unless I've missed something really obvious in differences... You never (generally) hear about Discovery 1 drivers complaining about any of these things, when in fact the disco is probably a bit heavier than a defender has the same engine and transmission (bar the 1.2 T box) and people tow with them all the time...

Thoughts anyone?

Mav

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My 100" had a 1.2 T Box. It was fine except when towing over 2 tonne, then you really noticed the gap between 3 and 4th gear. My 110 never had that issue with its 1.44 T Box, nor does my 200 Disco. Although oddly enough there's not a lot in tyres size difference

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Factor in that some people play with injection pumps will also have a bearing....

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The disco 200's where meant to have a few more horses where they not? that would probably help too... but I thought the 300's where the same between Def/Disco

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Yes, they did, and the 300TDI autos a little more.

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Correct me if I'm wrong but don't the main gearbox ratios differ between Defender, Discovery 1 LT77 and R380?

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Now this has bugged me for a while and I've found 2 minutes to finally get my coalesced thoughts down on paper...

You often get topics for people asking about how to improve the on-road abilities of the Defender - meaning wanting to increase fuel economy... reduce noise... increase speed etc ect. Amongst the options are installing an overdrive, putting bigger diameter tyres on, changing your diff ratio's and finally the changing of the transfer box ratio...

Now what really baffles me is that you get people whom have done the 1.4 to the 1.2 ratio box swap on defender I think mainly, then they usually complain that the gears feel too tall for the engine revs and people have trouble towing and all sorts of other complaints...

Now unless I've missed something really obvious in differences... You never (generally) hear about Discovery 1 drivers complaining about any of these things, when in fact the disco is probably a bit heavier than a defender has the same engine and transmission (bar the 1.2 T box) and people tow with them all the time...

Thoughts anyone?

Mav

The Disco normally has much smaller tyres than a Defender which reduces the overall ratio. Put some 205R16s on your Defender with a 1.2 transfer box and it will be fine... pretty much exactly the same as the Disco apart from the aerodynamic issues over 50MPH.

If you "upgraded" a Discovery to use the 1.0 transfer box (used on the early 3 speed auto RRC) they'd be having similar issues to a Defender running 1.2.

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Funny but I was just messing with this today

Same main box but with with 1.2 with 225/75R16 and 1.4 with 235/85R16 at 80MPH there is only a couple of hundred RPM difference.

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As has been said overall ratio including tyres is very similar.

I used my 90 1.4 fairly tweaked and disco milk float 1.2 little tweak for the same 25 mile cross country journey to work for ~ 6months each with the same set of wheels and tyres.

The 90 went better, was smoother to drive and did better on fuel.

Landrover got at lot of things right.

Will

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I was driving from Cornwall to Staffordshire every other week in an old 300tdi 90 about ten years ago. Putting an Allisport intercooler and 1.2 disco box in it was a massive improvement, I could sit at 65mph (GPS) rather than 60 and it would do the trip on one tank of fuel whereas before I would always have to stop and fuel up at Stone services.

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Having just fitted a 1.2 tbox to my 110, I thought I should just add my thoughts and it is much better!! While I haven't towed 3 tonnes yet, it pulled 2.5 tonne I for trailer with no issues across some steep Devon roads and still pulled my empty trailer back up Holden hill outside Exeter at 65 mph. It sits at 70mph on the motorway now at 2400 rpm and is just so much better. The engine does have a bigger charge air cooler and it is chipped, but unsure who did it or what stage if was done to other than it goes well. Boost runs at 1 bar and is the standard turbo so nothing serious.

All in all I am a happy bunny!!

Toby

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Now this has bugged me for a while and I've found 2 minutes to finally get my coalesced thoughts down on paper...

You often get topics for people asking about how to improve the on-road abilities of the Defender - meaning wanting to increase fuel economy... reduce noise... increase speed etc ect. Amongst the options are installing an overdrive, putting bigger diameter tyres on, changing your diff ratio's and finally the changing of the transfer box ratio...

Now what really baffles me is that you get people whom have done the 1.4 to the 1.2 ratio box swap on defender I think mainly, then they usually complain that the gears feel too tall for the engine revs and people have trouble towing and all sorts of other complaints...

Now unless I've missed something really obvious in differences... You never (generally) hear about Discovery 1 drivers complaining about any of these things, when in fact the disco is probably a bit heavier than a defender has the same engine and transmission (bar the 1.2 T box) and people tow with them all the time...

Thoughts anyone?

Mav

The big difference is the tyre size.

Disco's should run a circa 29" tall tyre, while a Defender on 235/265's or 7.50's should be somewhere around the 31-32" height.

This means the mph per 1000rpm in top for a Disco and a Defender as very very similar. Despite the transfer box differences.

Slap some 235/85's on a Disco and you'll typically get all the same issues people with 1.2's in Defender's moan about. More trouble pulling 5th, long gears and blunts the acceleration.

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Discos (mostly) run 205R16 tyres as standard, Defenders (mostly) run 7.50R16 / 235/85r16, a fair increase in gearing. Very rare to get tyres that big on a Disco (because of bodywork), very rare to find a Defender running round on 205's.

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Discos (mostly) run 205R16 tyres as standard, Defenders (mostly) run 7.50R16 / 235/85r16, a fair increase in gearing. Very rare to get tyres that big on a Disco (because of bodywork), very rare to find a Defender running round on 205's.

You find quite a lot of basic spec pickups and vans running round on 205R16. Disco 1 tyre size is 235/70R16 if I rememeber correctly? Either way its a big change in gearing between a defender and a Disco tyre wise.

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I can add some numbers to this.

With a 31.73" tall tyre (235/85R16) and the 1.41:1 transfer box with a 0.83:1 5th -- (standard Defender)

3000rpm = 68.4mph

With a 28.91" tyre (205/80R16) and the 1.22:1 transfer box with a 0.83:1 5th -- (standard Discovery 1)

3000rpm = 72mph

Very similar.

With a 31.73" tall tyre (235/85R16) and the 1.22:1 transfer box with a 0.83:1 5th

3000rpm = 79mph

It's also worth noting, there have been several different 5th gear ratio's over the time periods too. Which can also have an affect on the suitability.

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You find quite a lot of basic spec pickups and vans running round on 205R16.

You do indeed get a lot of 90's/110's on 205's. They tend to be more peppy and often suit the older 2.5TD. But will be less suitable to motorway cruising, although they can and will still cruise at 60mph no probs as a rule. Just noisy and high rpm.

Disco 1 tyre size is 235/70R16 if I rememeber correctly? Either way its a big change in gearing between a defender and a Disco tyre wise.

Depends on the exact year, spec and model trim. I think 205, 215 and 235 where all standard widths. Might even have been a few wider ones for the optional alloys. All are about the same height however. My p38a runs 255/55R18's as fitted by Land Rover, which are 29.04" tall. Same sort of ballpark.

235/70R16 = is a bit taller at 30.95"

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I used to run 7.50R16 tyres on the discovery when laning. I ran standard size the rest of the time because they did indeed make it perform like a stoned slug in high range :)

Used the same tyres on the V8 range rover that preceded it, and that suffered too, though it had a bit more grunt to spare. I still ran standard tyres for daily road driving.

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My 110 is a TD5 and is running 265/75 tyres so is now higher geared than a Discovery. According to the Ashcroft calculator it was doing 2900 rpm at 70 and should have dropped to 2400 rpm at 70 with the ratio change. The rev counter now indicates 2500 rpm but suspect the speedo is slightly out as the Nanocom agrees with the Rev counter.

Toby

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Now this has bugged me for a while and I've found 2 minutes to finally get my coalesced thoughts down on paper...

You often get topics for people asking about how to improve the on-road abilities of the Defender - meaning wanting to increase fuel economy... reduce noise... increase speed etc ect. Amongst the options are installing an overdrive, putting bigger diameter tyres on, changing your diff ratio's and finally the changing of the transfer box ratio...

Now what really baffles me is that you get people whom have done the 1.4 to the 1.2 ratio box swap on defender I think mainly, then they usually complain that the gears feel too tall for the engine revs and people have trouble towing and all sorts of other complaints...

Now unless I've missed something really obvious in differences... You never (generally) hear about Discovery 1 drivers complaining about any of these things, when in fact the disco is probably a bit heavier than a defender has the same engine and transmission (bar the 1.2 T box) and people tow with them all the time...

Thoughts anyone?

Mav

Because Defenders run on 235/85s while Discoverys run on 235/70s. That diameter difference makes all the difference (about 8% if I remember old calculations correctly, much less than the 13% step up in gearing from 1.4:1 to 1.2:1). So, a standard Discovery has a slightly taller final ratio than a standard Defender, but not enough to degrade performance. A 1.3:1 transfer ratio would be good for most Defenders, but I don't think there is one.

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111 300 Tdi

134 300 Tdi Auto

A little bit OT, but since it's been mentioned already, perhaps the Mods will allow me to ask what differences were there in 300 Tdi engines between the manual and auto versions? The difference, of 23 bhp, is significant and is of the order of improvement claimed by Allisport for their standard size upgrade.

Mike

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134hp is not correct. I think the auto 300Tdi's had 122bhp vs 111hp for all other 300Tdi's.

This was done by using an Bosch Electronic Diesel Control system, where the mechanical injector system was controlled by a drive-by-wire electronic throttle to reduce emissions.

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If Bull-bar Cowboy was still around he would point out the aerodynamics of the Defender as also having an effect on speed....

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