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 Post subject: Re: AWD Locost?
PostPosted: Thu Jul 21, 2011 9:14 am 
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Sorry and my apologies, at the DPCars site he states 65/35 for a planetary he has designed and not built yet but doesn't mention the ratio difference between front and rear, my confusion.

I will ask him what the ratio difference is.


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 Post subject: Re: AWD Locost?
PostPosted: Thu Jul 21, 2011 9:48 am 
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Location: Halifax, Nova Scotia
My wife came home with a brochure (now lost) for a new Subaru legacy the other day (she doesn't like her Forester after having had an Impreza) and one of the variants included a diff with 60/40 (or 70/30 - I forget) front/rear torque split, changing to 50/50 upon wheelspin. So this would give you rear bias drive when running 'backwards' - as long as you didn't smoke the tires! Lousy drag racer though. Wish I could find the brochure - but it probably got chucked.

Doesn't the STI have a rear-biased torque split, so the Legacy version of the diff is just the other way round to cater for sedate old f__ts?

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 Post subject: Re: AWD Locost?
PostPosted: Fri Jul 22, 2011 2:00 pm 
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I've done a bit of research into using an audi torsen center diff (like the one in the b5's/b6's), that will toss up to about 75-80% of the torque either way, if needed, and is set to 50/50 by default. The trouble would be in integrating it into an existing drivetrain, as it uses a very clever hollow shaft from the engine to the diff, with a solid one inside of it leading from the diff to the front, and a solid output shaft to the rear. It's more into the CNC'd one-off realm for our application, as I can't think of any existing drivetrain setup that would readily work with it, but if someone had the resources, it would make for a very slick awd solution.


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 Post subject: Re: AWD Locost?
PostPosted: Fri Jul 22, 2011 2:32 pm 
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Posts: 237
Location: Melbourne, Australia.
The whole issue of the type of centre diff to use is a fascinating area to research. There is no real best answer, every system has advantages and disadvantages under different driving conditions.

I do agree though that a torsen centre diff is probably the best all round choice for our type of driving, but cost seems to be a factor keeping it out of wider use.
At least one of the more recent top of the range japanese SUVs uses a torsen centre diff, but I cannot remember which vehicle.

The ubiquitous Jeep has been around for around seventy years, the very early ones were pretty crude, but since 1980 they have constantly changed the type of transfer case and centre diff from model year to model year over that time.

If you own a jeep, you can get quite a choice of centre diff type, by just bolting on the transfer case from the appropriate model year.

http://en.wikipedia.org/wiki/Jeep_four_ ... ve_systems

.


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 Post subject: Re: AWD Locost?
PostPosted: Fri Jul 22, 2011 4:01 pm 
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Location: san francisco bay area
New Venture (single speed version) 147. .. gerotor pump controlled by the speed differential between the 2 output shafts applies pressure to the clutch pack. Only available in left hand drop unfortunately. I've always liked driving QuadraDrive 2 vehicles as far as compliance and seamless operation, they use that method on both diffs too. Not a "full lockup" but on asphalt so what?

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 Post subject: Re: AWD Locost?
PostPosted: Fri Jul 22, 2011 7:22 pm 
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Location: Melbourne, Australia.
oldejack wrote:
Only available in left hand drop unfortunately.

It may be feasible to turn one upside down.
It would obviously require new drain and fill plugs, and the pump pickup modified, but the splash lubrication should still be pretty frantic.


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 Post subject: Re: AWD Locost?
PostPosted: Fri Jul 29, 2011 3:08 am 
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Just came across this 1970 DAF rallycross car using it's CVT midship, notice the extra roof height for the driver who straddles the drive train!


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 Post subject: Re: AWD Locost?
PostPosted: Fri Jul 29, 2011 7:04 am 
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Location: central Arkansas
That's the same layout I tried, until I realized I had to have a 1:1 drive somewhere. Otherwise you wind up with a 9:1 or so final drive, which would be great for a rock-crawler, but not so hot for freeway use.


Hmm... many years after I aborted that build, I found that the 4wd Honda Odyssey (?) was supposed to have a 1:1 rear differential. It wasn't intended to move much power though.

If you were building a 100-125hp car, you might be able to use a pair of those, though...


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 Post subject: Re: AWD Locost?
PostPosted: Fri Jul 29, 2011 7:19 pm 
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Location: Melbourne, Australia.
TRX wrote:
That's the same layout I tried, until I realized I had to have a 1:1 drive somewhere. Otherwise you wind up with a 9:1 or so final drive, which would be great for a rock-crawler, but not so hot for freeway use.

It might also make a good deep snow, or swamp buggy, with four really enormous large diameter wheels.


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 Post subject: Re: AWD Locost?
PostPosted: Thu Aug 04, 2011 2:19 pm 
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the Ford Sierra XR4 unders ..


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 Post subject: Re: AWD Locost?
PostPosted: Thu Aug 04, 2011 5:41 pm 
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Location: central Arkansas
That's the same setup Dax uses in the Quadra. All the twirly bits are on the driver's side on a RHD car, too. Even LHD, the passenger footwell is going to be narrower than it is tall...


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 Post subject: Re: AWD Locost?
PostPosted: Fri Aug 05, 2011 4:23 pm 
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TRX wrote:
That's the same layout I tried, until I realized I had to have a 1:1 drive somewhere. Otherwise you wind up with a 9:1 or so final drive, which would be great for a rock-crawler, but not so hot for freeway use.


Hmm... many years after I aborted that build, I found that the 4wd Honda Odyssey (?) was supposed to have a 1:1 rear differential. It wasn't intended to move much power though.

If you were building a 100-125hp car, you might be able to use a pair of those, though...


The original honda engine with those had 150-220hp, and hauled a 3400lb minivan around, plus passengers and cargo. I'm certain it'd be more than up to the task of handling a 250+hp, 1000-1400lb locost without much trouble, as long as you didn't do 10,000rpm clutch dumps at every stoplight. Too bad they were only available in japan. :\


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 Post subject: Re: AWD Locost?
PostPosted: Fri Aug 05, 2011 11:19 pm 
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Location: central Arkansas
You know, after I'd basically given up on the idea of 4wd, the Voices presented me with a workable possibility earlier today - for a conventional front-engined car, it's the width of the transfer case that's the problem.

...you could stand the transfer case up on end.

Even a small transfer case is fairly bulky, so you'd still wind up with a box six or eight inches wide and well over a foot tall, and the forward driveshaft and the shifter would have to play nice, but it's doable with ordinary bits. The forward shaft needs to miss the shifter, guide to the right, and clip off the top inboard corner of the passenger footwell to slide the shaft past the top of the bellhousing.

You'd need a joint there, and the second half of the shaft would snuggle right under the exhaust ports (assuming small block Ford power...) and down to the front differential. Depending on configuration, it might work better to move the transfer right back to the snout of the rear end (assuming IRS) and hoonch the rear bulkhead forward a bit to move the transfer case out of the cockpit entirely.

It's not a perfect solution, but its faults might be small enough to live with.

Of course, you need a lightweight transfer case with a viscous or Torsen differential. A quick web search showed only umpty-zillion different kinds of transfer cases out there. I guess I need to start making a chart to help identify them.


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 Post subject: Re: AWD Locost?
PostPosted: Tue Aug 09, 2011 8:22 am 
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Posts: 114
Location: Lincoln, NE
BAMM!!!

http://www.elliottmfg.com/index.php?id=3

i actually have first hand experience playing with these, they actually work...make them large enough to hold up to 300hp.

clock the xfer case up, then just run a flex shaft along side the motor


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 Post subject: Re: AWD Locost?
PostPosted: Tue Aug 09, 2011 5:38 pm 
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Joined: Sat Apr 16, 2011 11:05 pm
Posts: 237
Location: Melbourne, Australia.
TRX wrote:
Even a small transfer case is fairly bulky, so you'd still wind up with a box six or eight inches wide and well over a foot tall, and the forward driveshaft and the shifter would have to play nice, but it's doable with ordinary bits.


A one inch diameter solid rear axle shaft works just fine, a one inch diameter solid front prop shaft would work fine too.
It could go through a hollow tube which is part of the main chassis structure with some slim bronze bushes spaced along the length. No need for anything bulky.


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