AWD for Rear Engine??

[cord4530]

I've been toying around with the idea of building a dune buggy (manx style) that is set up for auto-x and street use. My big problem is that I'd really like to make it AWD. I'm a huge fan of the Torsen center diff that's found in many Audi's, and a transaxle from a 90's S4-S6 would be great. But the problem is that in a rear engine configuration the axles would rotate the wrong direction. And the diff isn't made to be flipped like in the VW/Porsche transaxles.

I guess I was hoping to see if anyone had some great ideas for getting around this problem. It may be possible to machine the case of the Audi transmission. The other option I've looked at is using the Porsche C4 transmission, but it's hella expensive, and uses an electronic control for the F/R torque split.

Anyway, if you have any ideas, feel free to post them up-

[talntid]

Dan,

Well, that sounds like a cool project. Have you checked any other AWD platforms such as DSM's (eclipse/talon/laser), or subaru or the evolution series?

[cord4530]

Thanks for the tips Eric. (And congrads on the new-to-you Supra). IIRC, the DSM's and EVO use a transverse mount engine, so I'd have to run the tranny in that configuration. The Subaru is another potential option, but most of the Scooby people were telling me their transmissions weren't all that tough :o( Still, it's worth looking in to because even though the car may have 350-400 hp, it's not going to weigh very much at all.

There is a chance I'd have to live with it as a RWD platform, and use something like the Porsche G50 transaxle. But with decent power and a rear weight bias I was hoping the AWD system would help keep the car a lot more stable through the corners. I'm pretty excited about designing the suspension too. Planning on unequal length a-arms up front with center-mounted coilovers on pushrods, and multi-link rear suspension. One very nice thing about the Manxter bodies is that they have a LOT of room for tires. I loved the last one I built....I just wished it had a lot more modern suspension and tunability.
Thanks again!

[talntid]

Well you are right, the DSM's and EVO's do have a very similar setup, but the later EVO's are different than the DSM's. If the car is light and all, then 300-400HP should not be that much of a problem for scoob trannies. If the DSM setup would work and you want a very strong transmission, you should check out www.shepracing.com - he builds nearly indestructible DSM transmissions.

[talntid]

Curious - What Engine are you planning on using - whatever mates to the trans you choose?

And welcome to the site! :)

[cord4530]

I'll look in to the EVO transmissions more. That's one I haven't explored at all. The EVO's are still transverse engine aren't they? To be honest, I've never really paid that much attention to the drivetrain layout of the car.

I'm planning to use a 2.5L Subaru and design my own twin turbo kit for it (likely a pair of large-frame GT15's or small-frame GT20's). I'm also trying to make it a 3-seater with center driver and two rear passenger seats. That's a LOT easier to do w/o AWD though.

It seems like there were a lot of AWD rally cars in the late 80's and early 90's that may be potential sources for a rear engine transaxle.

[cord4530]

Thanks for the site welcome too! I'm happy to see Spokanespeed back to life again!

[talntid]

So if you are planning on using the Subaru 2.5 motor, I would look into a lot of options including the Subaru XT drivetrain, as well as the Justy - they can be beefed up significantly. I do not think that using another drivetrain with the Subaru motor would be cost-effective. Have you looked at any of the European Rally cars that never made their way to the USA? (Pugeot, Cosworth's, Opel, etc..) They are all very beefy cars with tons of support outside the USA.

Also there is a type of electric car that is rear engine, all wheel drive that I will see if I can remember the name of. It can beat a vette 0-60, and electric motors put out massive amounts of torque, so it must be at least somewhat beefy. :)

[cord4530]

It's pretty easy to adapt the subaru to a number of different transmissions, so that part doesn't worry me as much. But having a bolt-in option has some apeal too. I'll have to take a look at a few Subaru transmissions to see how easy it would be to flip the differential. I'm sure none of them will be as simple as the Porsche/VW, but at this point I just need to see if it's even possible at all.

Yes, Euro rally cars are one of the sources I have not been able to find much about. I thought there were some rear engine AWD rally cars, and they'll likely have a pretty strong transmission as well.

Thanks again-

[4STFED]

Ide be interested in seeing some pictures of the last one you built. Sounds like a fun project! Good Luck!

[cord4530]

You know...I took several pictures during the restoration, but didn't take many of the complete project. Here's one of them:
http://www.webs1.uidaho.edu/dcordon/images/car_images/BUGGY2.JPG

The cars are a ton of fun. My last one was almost all VW parts though, and while simple, it would be nice to have more adjustability. I just loved the body and how much fun it was to drive around. And they're light! I could pick the front wheels off the ground by lifting on the front bumper. The next version I build is going to have a lot of attention given to weight distribution :o) I think I should be well under 2000 lb even if I go the AWD route. I will be building my own chassis and suspension this time around. The design of that should eat all my spare time for the next few years....

Bruce Meyers just released a new version called the Manxter. It's a longer wheelbase than the older models, and has some nice lines. Barebones kits are reasonably priced. (body, cage, and top). Here's some pictures of them:
http://www.webs1.uidaho.edu/dcordon/images/car_images/Manxter1.jpg
http://www.webs1.uidaho.edu/dcordon/images/car_images/Manxter5.jpg

Pay no attention to the rest of that site...I haven't really done anything with it :o(

[AWDfanatic]

Just to let you know the only Subaru tranny built to hold a decent amount of horsepower is the STi. The other ones including the WRX are only good for around 300hp before you start shredding gears...I know first hand :)

[cord4530]

Thanks for the tip Brad. I had kind of heard the same thing about the Scooby trannys. Heard a lot of WRX's people with high power complain about transmission failures. Hmmm...a 6-spd with electronic torque distribution....I'd love to implement something like that on the next buggy. Though I'm guessing the Porsche C4 tranny (G64) would be easier to use in this application. I just wish they weren't so expensive!

[cord4530]

Just an update on transmission options.

I called a few places about the Subaru and I've gotten the same answer. There's virtually no way to flip the differential in the Subaru transmission (w/o just machining a new case anyway). So that rules out the STi tranny.

The Audi torsen transmissions are similar. You *may* be able to machine the case to allow the diff on the other side, but the case would be pretty thin in a few spots.

There is a VW AWD tranny from the old aircooled van days. They're hard to come by, and just 4 spd transmissions with similar internals to all the other old bugs. Not a great match for the proposed project.

But there is one model Porsche that will work very well. The G64 gearbox from the C4 964 (89-94 911 Carrera 4) is a great match. It's a 5 spd (but can be converted to 6 spd for an arm/leg) and has a rear-biased mechanical torque split. There's also options to lock up both the center and rear differentials (used for traction control originally). None of the other AWD Porsche transmissions are well suited since they're primarily RWD only, but have the ability to send some torque to the front if necessary.

Thanks for all the thoughts/tips. Now I just have to find one of those drivetrains......