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just had a strange thought
cornishrob - 18/12/05 at 06:45 PM

after reading the following in another topic in this forum

quote:
Originally posted by dave dickson
I saw a race series at the local track a while back with a load of minis which were converted to rwd. The engine was mounted longitudinaly, with the driveshaft now facing forwards welded to the subframe to stop it turning. the diff then transfered all the power to the other shaft, which was lengthened and coupled to a rear axle of unknown origins.
It all loooked a bit bodged, but they looked like an absolute hoot to drive.



Has anyone ever heard of someone using a transverse 2wd engine and gearbox pairing to split power from a longitudinally mid mounted position to power all four wheels?

The old GRP B rally cars like the rs200 and metro 6R4's used mid mounted 4x4 engines but it has always puzzled me how their gearboxes worked and how i could replicate such a system in another car.

Oliver Coles - 18/12/05 at 07:01 PM

I think on the old metro 6r4 rally cars the transmission was similar to that of a land rover. Engine and gearbox in the middle connected to a diff which is connected by two drive shafts to a diff at the front and back. I think?

SixedUp - 18/12/05 at 07:20 PM

quote:
Originally posted by cornishrob
Has anyone ever heard of someone using a transverse 2wd engine and gearbox pairing to split power from a longitudinally mid mounted position to power all four wheels?


Hmm. Sounds feasible, provided you have an LSD in (at least) the main gearbox. Without that then you're never going to really have 4WD. As soon as a wheel on either of the axles starts to spin then all the power will go to that axle/wheel (depending on whether or not you have LSDs in each of the two axles).

I'm not sure how some of the modern "4WD" cars like the Audi TT work, where they are basically FWD until wheelspin sets in, at which point drive goes to the rear wheels too. I suspect fancy electronics though ...

Cheers
Richard

Oliver Coles - 18/12/05 at 07:28 PM

I think audi's are constant 4 wheel drive.
They have a engine slung in front of the front wheels and what is basically a normal gear box driving the back wheels. However, it also has two drive shafts coming out of the side to drive the front wheels.

Liam - 18/12/05 at 08:10 PM

Above idea has been discussed before. The problem is you already have your final drive reduction before what is now your centre diff. You'd need to source (more like make yourself) 1:1 diffs for the front and rear. Otherwise a very nice idea.

Audi A3 and TT are a part time 4WD system borrowed from VW - essentially front wheel drive until slip occurs. Conversely a VW passatt is a full on quattro.

Here's how a 6R4 works by the way...

Liam Rescued attachment 6r4layout.gif
Rescued attachment 6r4layout.gif

Daxrushv6 - 18/12/05 at 08:15 PM

i have the audi S3 which is a full quattro but is the same set up as the a3 and tt standardish fwd gearbox with transfer box bolted on which sends the drive too the rear diff. The difference with the S3 is that its intelligent and sends the power to the wheels with grip.

iank - 18/12/05 at 11:46 PM

As Liam says the problem is the final drive ratio, i.e. needing 1:1 (ish) diff ratio on either end.

I've heard that some of the sporting trials guys (the tiny things with bike front wheels, and a passenger who bounces up and down ) weld the diff of a transverse engine and use one long driveshaft to a live axle to get an insanely low ratio so they can climb muddy hills better.

[Edited on 18/12/05 by iank]

cornishrob - 19/12/05 at 06:15 PM

Sixedup, im not entirely sure on the new VAG 4x4 systems, But they do have transverse front mounted engines much like the celica GT4 and Mitsubishi evo. where the drive from one driveshaft is put through a transfur box mounted to the gearbox and then connects to the prop. I dont know however how they can get this to stop power going to the rear wheels.

On the subject i would rather use ATB differentials over LS as it would act more like the traction control system in the skyline GTR's putting the power to the wheels with traction.

Oliver, much like the 4x4 cosworths and subaru imprezas mounted longitudinally, a far better way imo but has a lot of weight in the nose.

With the subject of dif ratios i see the point but dont understand fully. I take it using a dif sorced from a sierra would cause a furthur reduction in final drive?

quattromike - 19/12/05 at 08:06 PM

quote:
Originally posted by Daxrushv6
i have the audi S3 which is a full quattro but is the same set up as the a3 and tt standardish fwd gearbox with transfer box bolted on which sends the drive too the rear diff. The difference with the S3 is that its intelligent and sends the power to the wheels with grip.

So it's more like a caviler or calibra 4x4 with an abnormal diff in the back of the gearbox and a transfer bos in one side with a hollow shaft for the drive out to the right wheel an two clutches on the transfer box to control the drive to the rear wheels.(yes i did have a mate with a cavy 4x4 turbo which had problems in the transfer box). don't like it give me my old quattro any day

Mike

iank - 19/12/05 at 08:44 PM

quote:
Originally posted by cornishrob
...
With the subject of dif ratios i see the point but dont understand fully. I take it using a dif sorced from a sierra would cause a furthur reduction in final drive?


you are going to be transmitting drive through the diff in the transverse engine/gearbox unit and the diff's at either end. So you get to multiply the diff ratios, thus getting super low ratio.

Using round numbers, and assuming the diff in the transverse assembly is 3:1 and the diff's front and rear are also 3:1 (not 100's of miles away from typical roadcar values) The effective diff ratio's are 9:1 which will be like running a 4x4 in low range all the time, not much fun in a sportscar

Liam - 19/12/05 at 09:23 PM

quote:
Originally posted by quattromike
quote:
Originally posted by Daxrushv6
i have the audi S3 which is a full quattro but is the same set up as the a3 and tt standardish fwd gearbox with transfer box bolted on which sends the drive too the rear diff. The difference with the S3 is that its intelligent and sends the power to the wheels with grip.

So it's more like a caviler or calibra 4x4 with an abnormal diff in the back of the gearbox and a transfer bos in one side with a hollow shaft for the drive out to the right wheel an two clutches on the transfer box to control the drive to the rear wheels.(yes i did have a mate with a cavy 4x4 turbo which had problems in the transfer box). don't like it give me my old quattro any day

Mike


That's correct. Quattro by name only - the system is very different to the 'proper' quattro system in the bigger cars (traditional three mechanical diffs - full time 4WD). The longitudinal quattro arrangement simply wont fit in the TT/A3/VW Golf platform. Still it's a lot more developped than the old cav system though - the front/rear coupling is at the back between the prop and rear diff for better weight distribution, and is an electronically controlled hydraulic clutch rather than a 'brainless' viscous coupling. I believe the S3 also has an electronic slip limiting system in the front diff.

All in all a perfectly effective system capable of providing excellent traction. The essential difference to a full time 4WD system (especially one with a rear power bias) is that it requires the front axle to be on the very limit before significant power goes to the rear. Or to put it another way, the situation where excess power slips the rear axle whilst the front axle still has grip is impossible. I.e. fun stuff like power oversteer can't happen. An old sierra 4x4 on the other hand with its full time rear biased 4WD system is perfectly capable of lairy powerslides, and boy is that fun on a low friction surface (or on dry tarmac with enough engine power). Vastly more fun than 2 wheel drifting in a RWD car in my opinion - one of the reasons my locost is 4WD

Liam

cornishrob - 20/12/05 at 05:05 PM

My celica GT4 was permament 4x4 with a transverse engine in the front, 70% rear 30% front split on power, tends to handle more sideways than the scoobs and evos and fantastic to drive, i miss it so much , but better things to come.


I see the problem with the differentials then and custom items would need to be used to make it faster as such.