Hi, im planning my next project that is going to be mid engine 4wd using a 3.0 nissan v6 twin turbo rwd engine/gearbox mounted backwards like a metro 6r4 with a reverse transfere box and cosworth diffs but there wont be a centre diff. Do you think this will work?

James

 

 

When you say there wont be a centre diff, what will there be instead?

 

Hi, Where the prop shaft would usually bolt to the gearbox there will be a custom transfere box simular to this..

http://www.milneroffroad.com/TBOX.HTM

So there would be no centre diff, im just trying to work out how it would drive, if its going to drive like a dog then i wont bother. I know some cars had permenent 4wd like the old audi s1 but i presume they still had a centre diff.

thanks

Ive just noticed that company actually do a transfere box with a centre diff too, hmmm.

I have wanted to build a 4wd mid engine car for ages now and this is the is the only way i can think of.

 

I think it will need a center diff or it will just understeer
Like a car having 2 engines and not being able to bias the torque
Good at santa pod

 

It would be fine for off road, but on the street it would be a pain.

No centre diff would mean that the front and rear axles would have to turn at the same speed. This would appear to be fine in a straight line, but once you start to turn a corner the rear wheels take a slightly tighter corner than the front, so the axles are trying to turn a different speeds. The prop shafts and halfshafts would tighten up until one tyre slipped or something broke. This is called windup, and is the reason 4x4s wear tyres if they are left locked in 4x4.

You also get problems if the tyres are inflated at different pressures, or have different tread depths.

The best setup for the street would be centre and rear LSDs with an open front diff. This stops the steering getting too heavy at low speeds i.e. when parking.

Hope this helps.

The best setup depends on what you are going to use it for.

 

 

Thanks for the replies guys, the above transfere box does actually have a centre diff, would this be any good do you think? the car is going to be a track car so i want it to handle good.

 

This looks as if it is either open, or locked solid. You really need a slipper differential if you are wanting good performance on tarmac.

It might be easier to take all of the 4x4 parts from an existing vehicle that is already set up for road use with permenant 4x4, or at least the centre diff arrangement.

 

If you want to run as per 6r4 etc you could use a standard 4x4 box running forward from the engine (gate would then be reversed so would take some geting used to) with a 50/50 split fitted and then just flip the diffs over so that they rotate forward.

 

I have got in contact with the company that makes those transfere boxes today and they can build one with a slipper diff inside, they are getting back to me with the exact spec, so do most 4wd cars use a slipper diff?

How does the slipper diff actually work?

If a centre diff was an open diff would the front 2 wheels just spin if they were on an ice patch etc?

 

Ive thought about this but i think on a cosworth etc the rear gets more torque split so with it all turned round the front would get more torque and i carnt think of a way to rererse it.

 

Yes, if the diff was open, and the front wheels spun on ice, there would be no drive to the rear.

The slipper diff allows the axles to turn at slightly different speeds for corners without winding up, but still provides drive to the other axle if one has no grip.

The best combination would probably be slipper centre and rear, with open front, as it will give more predictable handling.

The torque split front to rear will really depend on how much is available from the engine. The front will reach its limit before the rear, so if you have lots of torque, then you may have to bias it to the rear to make the car driveable. The rear bias will tend to encourage power oversteer.

 

thanks mate, The guy from milner off road could of bulit me a suitable transfer box with a gripper diff built in but its worked out too expensive really.

im now wondering what the torque split is on a mt75 box? could there be a way of altering it? if so i could spin it round maybe, or a skyline gearbox? i think the centre diff is controlled by a hydraulic system?

theres got to be a way to do do this?

james