i dont understand why you woudnt just mount in normally and use the axles to your wheels? why do you want to tunr it sideways and run to another diff? whats the point? whats the advantage, orther than working for a logging company? lol jk.. it seems like way more work, worse end results... why?
Not worse end results. And not really that much more work.
Mounting a typical front drive engine like it sits in the car from the factory means one shaft will be way shorter (Unless its one of those bigger Audis that still use the center diff with equal shafts). Not a big deal on a street car with 4-5 inchs of travel. Plus the gearing is rarely deep enough. Now if you went like Chain drive rails you could tailoer the ratio easily to your needs. Those chains are longer and massive and I have not heard of them having ANY chain issues.
http://www.chaindriverail.com/indexcon.htmhttp://www.sandrocket.com/If you look at Sand rockets they use an IRS rear end out of a Jaguar fed by a front mounted V-8 engine and automatic transmission. Makes for a pretty nice sand machine (Not sure how they do on other terrains) One could also use the rear end out of late model ThunderBirds or Vettes and others.
Now if you take a typical decent running light weight front drive assembly and tranny and turn it sideways you simply run power off it to a IRS rear end for a setup that could have the motor in the front like a Sand Rocket or it could be hovering right on top of the IRS like a Midengine VW rail is. Not quite as short but dang close.
The issue may be the ratio but with a front transaxle geared for tiny tires the typical 3.08 ratio in an IRS rear would be a benefit I feel. Plus no doubt there are higher ratios already in IRS rear ends if a person looked. I do not see this as anywhere NEAR a rock crawler ratio. Nor a log hauler....
When I first thought of this it was looking at a VW Rabbit. Decent spirit and a tranny that could shift like greased lighting. But the tires on the front were TINY. To get them to turn 1300 Padla Tracs would NEED a 3 to 1 type ratio.
Plus the rabbit would run 100 MPH like nothing. Unless your running Baja you realitically are not going to be needing to go over maybe 65-70 tops and since most off roading involves hills (and steep hills if your like me and have my kind of fun) the ratio will be decently suited with large sand tires or small truck 4x4 tires if you are a hardpack runner.
Plus if you could use an automatic tranny (providing its mounting would not starve the tranny pickup for oil (or the motor for that reason) due to the different forces imposed on it) you would NEVER miss a shift. An Automatic in a light car is always fun if the motors got a lil pep.