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Top speed vs transfer box ratio?


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Hi I have read countless threads ect about top speed in a 90 200 tdi conversion ect , but not many mention transfer box ratio. My own conversion 90 it's fine for me but I was just wondering mine says 1.4 ratio the  acceleration  is fine as quick as wifes freelander 2 to 50 it pulls fine even up the local hill god knows what slope , I can come up at 40 in 5th and still pull. I can get to 65 on the motorway but it's starting to get noisy but feels any more I am just revving with not much pull left. Question it pulls fine with a trailer on or not just slightly slower up hill but not much ,so I am reading all this about 80 mph ect is that with a 1.2 transfer box or the standard 1.4 because the revs I would need to get to 80 would be ,well you not drive it ,I would feel like you were trying to blow it up or do I have something   someones changed the ratios in? First 90 so no previous experience had disco 2 for 10 years. It pulls well every gear 1-5 then stops pulling about 65. Any advice welcome andy

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Mine has a 1.4 box and will do 75mph without issue other than the noise. It sounds worse than it is as it’s a noisy engine at the best of times, the ratio calculator on the Ashcrofts website will show you that even at that speed you’re comfortably below the engine redline. With the overdrive in it’s comparatively quiet at 75 - just a shame about the fuel consumption, which plummets over 60-65!

Gearbox may make a difference, do you know what variant of LT77 you have? Some have different ratios for fifth gear. 

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Right I dont know what lt77 I have I need to look, well I must be that because the turbo pulls well every gear boosting , cant believe it not boosting right. Its reving high at 65 pushing it up every mile seems like it at full pelt. It must be something to do with the gearing, I had a tachometer on the engine max reves 4200 odd but god its loud. It's got to be gearing you would never get 80 out of it had 75 once downhill very loud. So yous guys are saying 1.4 box 80 on the flat, not that I am wanting too scream along at 80 more power lower down would be good but I am convinced it must be gearing but I could be wrong I think its f gearbox series from memory, there a thing I put a new cog in the lt230 final drive drilled and new main shaft what if I put in the wrong one would that alter the ratio and make it lower??

Edited by andy _1
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For a standard Defender LT77 as used in the 200Tdi vehicles (0.77:1 fifth), 4200rpm would be over 100mph. Even with the lower ratio LT77 which yours might be (0.831:1 fifth) the same revs gives over 90mph. 

That’s with 32” tyres, 1.4 transfer box and standard 3.54 diffs. A 90 from the factory would likely have had 205R16 tyres which would give lower top speeds. Your rev counter might also be out.

What age vehicle is it and what size of tyres do you have?

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Those tyres are in theory 29.9” diameter. In that case, with the early 90/110 LT77 and a 1.4 LT230 you should be doing about 90mph at 4200rpm.

Have you checked the speedo against a GPS to ensure that it is accurate? No aftermarket diffs fitted that could be different ratios?

As I say the noise can be misleading. Before the overdrive 75+ mph in mine was not pleasant and certainly straying into the ‘feels like it’s going to blow up’ territory, but it was only around 3,000 RPM. And that is with soundproofing - without it’s even worse. Especially if there are panel gaps etc. 

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41 minutes ago, andy _1 said:

1989 90 with a 200 tdi disco engine 235/75/16. Well there has to be something wrong then .

It sounds normal to me. My 90 on 33" would get to 80/85 happily... but its just a noisy engine (and car for that matter!). So any comparison to a 'normal' car is fairly pointless.

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I’m not sure why you would want to do over 70mph in an old Land Rover.

These are basically farm vehicles and not designed for the motorway.

Having said that the TD5 isn’t bad at motorway speeds, my mildly remapped 110 SW will easily do over 80 mph (where legal) but at that speed it’s clearly out of its comfort zone.

l am happy to sit at 65 mph which seems to be the best speed for this vehicle.

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Right I start looking nothing else to do in this government imposed tyranny.  I dont want to fly about over 70 mph but it means that I am not get full power in the lower gears as well. I will report back if i find anything , because there is nothing worse if someone in the future read the thread and there is no conclusion. 

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Your tyre size is your perceived problem. I had 205's (29") on my ibex for the IVA it would accelerate like a rocket but was noisy and had a lower usable top speed. If you want to change it see if you can borrow a set of 235/85x16 or 265/75x16 both were standard fit on 110 and optional on 90's. Try these and see what you think before committing to anything. Personally I really like the combination of 200tdi, lt77, 1.4 transfer box, standard diffs and 33" tyres (255/85x16, 285/75x16 and 33/12.50x15 are all around 33"). It's the combination I run on both my trucks acceleration is ok, will cruse at 70mph happily and still tow (I do quite a bit) acceptably.

Mike

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As said above, tyre size will make a big difference. And the noise you hear might not mean it's over revving. Do you have a rev-counter? Have you checked the speedo with a GPS? It sounds like you don't really have a problem, just that it doesn't feel/sound comfortable above a certain speed.

For reference, my 90 (TD5 with R380 and 1.4, so basically same ratios) would do 92mph (on GPS) on standard 205R16s and about the same on bigger tyres, then using 4th instead of 5th.

Filip

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16 hours ago, Lightning said:

I’m not sure why you would want to do over 70mph in an old Land Rover.

I paid for the whole speedo, I'm going to use the whole speedo :SVAgoaway:

I reckon OP's problem is just tyre size and the fact it's a rattly old TDi

A TDi in good shape should pull 80mph but the laws of physics dictate it won't get much further due to (the complete lack of) aerodynamics.

Also second actually measuring the speed with GPS, LR speedo's are not exactly precision instruments! :P

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You are right ^^^. Best of all worlds then and the current tyre choice on the OPs vehicle would probably work quite well. 

My 110 200tdi on 265/75/16s with a GKN overdrive and a 1.4 TXB cruises well at 70-late 80’s. Very happy at 80 on long runs (across France of course :) ). There would be more there but the gearing gets too high for the engine without a tail wind!

Edited by reb78
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Back in the early 90s, I converted my 2.5 petrol 90 to 200 Tdi. The engines were not easily and cheaply available then, but I did get a Defender spec engine for it.

It had the petrol LT77 with 0.831 ratio 5th gear, 1.410 transfer box, and standard diffs, but did have 235/85/16 tyres. I found it to be OK but noisy at speed, but would do 80 mph no problem.

It could NOT pull heavy (2 ton plus) trailers happily though. I did try a 1.222 transfer box for a time, and was OK for cruising, but it was hopeless at towing as it was overgeared. I borrowed some 750/16 BFG Trac edge shod wheels, and this was much better.

Ultimately though, I went back to the 1.410 transfer and 235/85/16s

It does not take much to completely hobble the vehicle.

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6 hours ago, miketomcat said:

My ibex Speedo (stock disco 1 system and tyres) read 13mph fast at 70mph. Ironically when I change the tyres from 29" to 35" the Speedo was bang on. Now on 33" and the Speedo is a couple of mph out which I can live with.

Mike

Sounds a bit odd. While it’s normal for speedos to over read a bit. 13mph seems way too much. And correcting itself on 35’s??? Maybe it has the wrong speedo drive?

My 200Tdi D1 would under read on 33’s. 

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14 hours ago, Lightning said:

Well the best solution is to fit the Roamerdrive overdrive unit, but it’s expensive.

I'd say that's way off the mark - OP's problem seems to be far more basic, either his 90 has something basic wrong with it or he's just over-sensitive about the awful noise a TDi makes at high speeds :lol:

Pretty much any old 90 should be able to hit 70-80mph on the flat unless there's something wrong with it - and bearing in mind the age of an average 90 there's loads of stuff that can hurt performance after 20+ years. Maybe a damn good service would restore it - it may have never had the tappets adjusted since it left the factory.

If it can't pull 80mph in 5th now it likely won't pull it with an overdrive.

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Yes you are right.

But I was thinking more of once he gets the engine performing as it should.

We had a 300tdi and it seemed happiest at 60mph on the motorway. I’m sure it would have done 80 if l’d kept my foot down long enough.

Its not just the engine that’s noisy at higher speeds, once you get past 70mph the general din increases significantly.

Still not sure why you’d want to do 80mph in an old Land Rover!

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If he gets it performing OK then in a 90 it should pull a Disco/RR transfer box (1.222:1) which is about £1450 cheaper than an overdrive unless you are regularly towing heavy loads and need the low gearing AND the cruising. We've got the 1.4 LT230 + OD combo in the ambulance and it's glorious but thankfully didn't cost anywhere near full price.

I find bimbling along behind the trucks gets pretty tedious after a while, especially if you've got 1000 miles to cover.

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