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Need better top speed


Gareth Dickens
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Is there enough power in the 2-1/4 engine to propel the vehicle at that speed at 2500 rpm?

I can't suggest a gearbox, but you want the type where the 5th gear is an overdrive gear rather than a direct drive.

If you're thinking of a Defender gearbox, these have permanent 4WD so you'll need to replace the UJs in the front axle for CV joints.

Overdrive would be the simplest solution.

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I want to increase my top gear cruising speed. Thinking of a 5 speed box. Still running 4.7 :1 diffs. Want to be able to cruise at aprox 120 - 140 kph ( 75 - 90 mph) @ about 2500rpm.

dont we all! you will need a 5 speed mated to a hs t-case to get that. (or a six speed, good luck!) and a dirty big motor to chug along at low revs. anyway, whats the hurry? imo - just chill, enjoy the scenery, it's not a race.

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If you're thinking of a Defender gearbox, these have permanent 4WD so you'll need to replace the UJs in the front axle for CV joints.

You can convert the LT230 to 2WD, it's easy, the kit is £140 ish from Ashcrofts. Series overdrives are cheap but do whine a bit, so the engine noise is replaced by whining and a trail of oil (at least mine seemed to eject oil from the vent non-stop). Isn't there a high-ratio transfer case for the series, that would get my vote if you had to stick to a Series transmission.

Personally, by the time you've mucked about with it you're better off buying an engine and box(es) from a Range Rover and dropping the whole lot in. An early 3-speed auto transfer box will have 1:1 high range which will give you a decent cruise, and low range will be very low due to you keeping the Series diffs.

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Is there enough power in the 2-1/4 engine to propel the vehicle at that speed at 2500 rpm?

I can't suggest a gearbox, but you want the type where the 5th gear is an overdrive gear rather than a direct drive.

If you're thinking of a Defender gearbox, these have permanent 4WD so you'll need to replace the UJs in the front axle for CV joints.

Overdrive would be the simplest solution.

I have a 4.2l V8 and need the legs in top gear as the motor starts to scream at relatively low speed. (even with 33" tyres) I was hoping to use some sort of diesel box as their ratios are usualy longer to compensate for hte low revs.

Here in South Africa we can easily do a 1000 miles to a destination. Imagine the fuel and time that would take going slowly in a high revving V8.

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dont we all! you will need a 5 speed mated to a hs t-case to get that. (or a six speed, good luck!) and a dirty big motor to chug along at low revs. anyway, whats the hurry? imo - just chill, enjoy the scenery, it's not a race.

Hey ozzy,

couldn't you suggest a Toyota gearbox and xfer case? (Hilux or Cruiser)

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I have a 4.2l V8 and need the legs in top gear as the motor starts to scream at relatively low speed. (even with 33" tyres) I was hoping to use some sort of diesel box as their ratios are usualy longer to compensate for hte low revs.

Here in South Africa we can easily do a 1000 miles to a destination. Imagine the fuel and time that would take going slowly in a high revving V8.

Nice One!

In that case rather than converting the gearbox to 2WD I would definitely convert the front axle to permanent 4WD because the extra torque on the rear diff will soon wreck it. I understand this is one of the reasons the original Range Rovers were permanent 4WD.

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Hey ozzy,

couldn't you suggest a Toyota gearbox and xfer case? (Hilux or Cruiser)

hey mr south efrika ;)

dont know much about toyota stuff or anything else for that matter!

the problem is the diff ratios..... 4.7 is too low for any old school gear box, they all will, when overdriven still return around

3000 rpm @ 100kph. anyway not such a problem, just wear ear plugs and cop the extra fuel bill. (or do a diff ratio swap and comprimise low range ability)

anyway, my S3 will sit on 120kph all day at around 3300rpm no problems, at this speed wind noise far exceeds engine buzz - is never going to be a shiny turd. such is series life.

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You didn't say you had a V8 in it :rolleyes: in that case I would highly recommend putting a Range Rover LT77 or R380 behind it and an LT230 as the 4.2 will eat a Series gearbox. If it's a SWB you may have a tight squeeze on your hands but it's possible.

Would that address the original issue - i.e. lower revs? I suspect Ranger Rover diffs would be required too. I had an early Rangie gearbox with higher ratio gears in the transfer box.

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Would that address the original issue - i.e. lower revs? I suspect Ranger Rover diffs would be required too. I had an early Rangie gearbox with higher ratio gears in the transfer box.

You can do it two ways:

- Keep the 4.7 diffs, run a 1.003:1 LT230 from a 3-speed Range Rover and have good cruise and a lower low box (which I like the sound of)

- Drop 3.54:1 diffs in, use a 1.222:1 LT230 from a RR or Disco and have standard RR ratios all round.

Many say the 3.54 diffs are stronger so that may be a consideration, depends on your driving style really.

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I have never looked inside the gear/transfer box. But I've read somewhere that it's possible to change some parts so that all gears get a lower ratio. True or not?

If you are refering to series then S2a suffix B low range spur and idler wheels will fit a later transfer box giving an untouched Hi range but a lower Lo range.

If you want both Hi and Lo to be lower then you want a complete transmission from a 1 ton.

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A friend of mine is trying to convince me to opt for a auto box with overdrive. What RR/LR auto boxes are available,how many gears do they have? Are there any where the top gear is allready overdriven (as opposed to direct drive)? Apparently auto boxes are softer on props and drivetrain. I have a 109 so space shouldn't be a problem. I would prefer a 4 speed auto box.

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A friend of mine is trying to convince me to opt for a auto box with overdrive. What RR/LR auto boxes are available,how many gears do they have? Are there any where the top gear is allready overdriven (as opposed to direct drive)? Apparently auto boxes are softer on props and drivetrain. I have a 109 so space shouldn't be a problem. I would prefer a 4 speed auto box.

Unless you're looking very modern, you have two types that were fitted to RR's:

TF727 3-speed (early, very strong but big and heavy)

ZF4HP22 - The 4-speed that's in a million Range Rovers and discos.

Neither involve any electronics.

I think this overdrive talk is confusing you - most manual boxes are 1:1 in 4th and overdriven in 5th (most LR boxes are around 0.75:1 in 5th, which is close to the 30% gearing an overdrive gains you over 4th). Not sure about autos, the torque converter mucks up the calculations a bit but the 4-speed works out similar.

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One thing to think about - is the rest of the vehicle up to the job? My series 3 (2.25 petrol with fairey overdrive) would do 70mph, but you could tell by the noise that it wasn't happy. At 50, everything chugged very nicely. Are the springs / shocks up to the extra speed? What about the brakes? Remember that if you double the speed, you quadrouple the energy, and therefore the power needed to stop. Making these things go fast is relatively easy - doing it in a way that won't kill you when something goes wrong needs a bit more thought.

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Unless you're looking very modern, you have two types that were fitted to RR's:

TF727 3-speed (early, very strong but big and heavy)

ZF4HP22 - The 4-speed that's in a million Range Rovers and discos.

Neither involve any electronics.

I think this overdrive talk is confusing you - most manual boxes are 1:1 in 4th and overdriven in 5th (most LR boxes are around 0.75:1 in 5th, which is close to the 30% gearing an overdrive gains you over 4th). Not sure about autos, the torque converter mucks up the calculations a bit but the 4-speed works out similar.

Apparently you have approx 2% slip through torque converter once stabilized at high power setting (modern torque converters)

What box to use then? 30% over in top sounds good enough. Just remember finding gearbox conversion kits here is hard. Changing diffs not really an option.

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What box to use then?

Well, anything - Range Rover or Disco or Defender, LT77, R380, 4HP22... they all go about the same speed when in front of the same ratio LT230. With a V8 you can probably get away with a 1.222:1 (RR/Disco) LT230 unless you fit huge tyres when you may want a 1.4:1 from a Defender.

If you get a setup from a V8 Range Rover or Disco it should bolt to your V8, and they're the most common version hence cheapest.

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