gearing ratios in transferboxes

[wee_arthur]

hi there,

we just purchased a a rang rover 3.9 v8 auto. This will be used to replace the 3.5 and manual gearbox from our (nearly) challenge spec 90. So the question is what transferbox will give us the best gearing for 35" tyres the original from the v8 90 or the range rover?

And also will there be any combination of 3.9 and auto that will equate to the same legnth as the manual 3.5 as we really cant afford to move the engine or the gearbox mounts?

Thank you in advance

[T1G UP]

been doing my research on this subject.

TB lowest ratio is 1.6 then you'll need some 4.1 R&P's

or 1.22 and 4.75's for loooow low range.

Very spendy though

[p76rangie]

hi there,

we just purchased a a rang rover 3.9 v8 auto. This will be used to replace the 3.5 and manual gearbox from our (nearly) challenge spec 90. So the question is what transferbox will give us the best gearing for 35" tyres the original from the v8 90 or the range rover?

And also will there be any combination of 3.9 and auto that will equate to the same legnth as the manual 3.5 as we really cant afford to move the engine or the gearbox mounts?

Thank you in advance

They all have the same low range, so for offroad there is no difference. The defender boxes have a lower high range to suit bigger tyres on the highway.

[FridgeFreezer]

Google Gearratiocalc.xls or look in the tech archive for gear ratio calculator.

[wee_arthur]

They all have the same low range, so for offroad there is no difference. The defender boxes have a lower high range to suit bigger tyres on the highway.

Thanks thats what i was pondering so as it is only for competitions what transferbox should i use and why? the borg warner from the range rover or the transfer box from the genuine v8 90 ?

thanks again

[FridgeFreezer]

The BW has no centre difflock, just a viscous coupling. Some love them, some hate them. Up to you really.

[T1G UP]

have a play on this http://www.solemnwar...t/transmission/

Personally i love the RR borg warner TB.

But ALL LR TB's have the same low range ratio, only way to alter that is by changing the ring and pinions. Thats the way i will do it.

[Bowie69]

WELL, you say that... but.... I spoke to a company that do a chain and sprocket conversion for the Borg Warner box, which drops the gearing in both low and high by around 25%. About £600 from memory.

It's quite a well known company, I've just got a mental block atm

[Dave W]

A 3.9 auto needs a 1.6 transfer box to pull 35s comfortably at motorway cruise speeds. Any higher and you need to keep kicking it down on slight inclines. The RV8s don't really have much below 2000 RPM so you need to cruise at around 2500 or above at 70

Your 90 TB is probably 1.4 so the 3.9 will just about pull it but it'll be heavy on fuel if you're doing any long distance work. The Range Rover will have a 1.2 in it which is fine on 205r16s but as soon as you start going bigger it'll start to be ungainly to drive.

[wee_arthur]

okay so for a future challenge truck with 35" simex's the 90 tb would be better?

I take it the actual physical legnth is the same for them both and the are easily swapped?

thanks

[Dave W]

They're all the same overall length although the BW front output housing is shorter so uses a longer front propshaft.

[Dave W]

Oh, sometimes the ZF auto output shaft only has splines for half it's length, this is fine for a BW transfer box but for an LT230 you need full length splines. The output shaft is easy to swap over though and not expensive to get hold of if you do need one.