Rear transaxle conversion

[xwd]

Yeah I was going to say if you want to use a transaxle, get one out of a Corvette, not a mid-engine Porsche. In the end I don't think the Porsche transmissions are that much better to be worth the effort.

[Spartarus]

Originally Posted by gtpvette

I'd say this or a C5 or C6 transaxle would work better. These boxes are made to be remote from the motor.

They are, however in those transmissions the gearbox is in front of the axle centerline, and would not fit due to the saddle fuel tank location. The Porsche box and rear housing fits behind the fuel tank, and only interferes with the muffler, which can be removed.

Originally Posted by wheelhaus

Couple questions... What's the purpose of a torque tube, why not use the driveshaft? Where would the clutch go, by the engine of trans? I guess it would be easier at the engine, but I'm not sue how well the driveshaft would balance at 7400 rpm. What speed does it spin on a stock drivetrain at 150mph?

1. I hadn't thought about that, but I suppose a driveshaft could be made without a torque tube... But would still need two bellhousings, except with slip yokes or flange connected to the input shaft. And a custom output shaft on the engine side... And bearings... It's doable though.

2. Clutch and flywheel stay where they are, driveshaft or tq tube internal shaft turn at engine speed. No problems there, most custom driveshafts are balanced to ~8000

3. Trivia. Stock driveshaft rpm @ 150 MPH = 8401.9
[The tires (215/45 R17) have Circumference = 77.3" Revs/Mile = 819.7. 150 MPH = 2049.25 wheel rpm, multiply by stock final drive 4.10:1]

[brianhj]

Originally Posted by KoolBRZ

Am I the only one to notice that he'll have 1 forward speed and 5 in reverse? This transaxle is meant to be in front of the engine, not behind it. Unless it's from a front-engine Porsche, like the 944, or 928, in which case you'd already have a torque tube and custom bellhousings from the donor car.

No

[FirestormFRS]

Originally Posted by KoolBRZ

Am I the only one to notice that he'll have 1 forward speed and 5 in reverse? This transaxle is meant to be in front of the engine, not behind it. Unless it's from a front-engine Porsche, like the 944, or 928, in which case you'd already have a torque tube and custom bellhousings from the donor car.

Always good for a laugh!

[wparsons]

Originally Posted by gtpvette

I'd say this or a C5 or C6 transaxle would work better. These boxes are made to be remote from the motor.

Same thing for 928's (and 944's too for that matter):

[Ultramaroon]

Originally Posted by KoolBRZ

Am I the only one to notice that he'll have 1 forward speed and 5 in reverse? This transaxle is meant to be in front of the engine, not behind it. Unless it's from a front-engine Porsche, like the 944, or 928, in which case you'd already have a torque tube and custom bellhousings from the donor car.

I think he just needs to flip it upside down. He'll be ok.

[Spartarus]

Originally Posted by KoolBRZ

Am I the only one to notice that he'll have 1 forward speed and 5 in reverse? This transaxle is meant to be in front of the engine, not behind it. Unless it's from a front-engine Porsche, like the 944, or 928, in which case you'd already have a torque tube and custom bellhousings from the donor car.

Originally Posted by brianhj

No

Originally Posted by FirestormFRS

Always good for a laugh!

Originally Posted by Ultramaroon

I think he just needs to flip it upside down. He'll be ok.

<- That's a slow clap. good observation, but wrong.

no, the boxster and cayman are mid-engine. *sigh* that transaxle goes behind the engine... A fact that has already been pointed out in this thread. Thanks though, I didn't consider the 944 or 928 transmission, though I suspect if the gearbox is in front of the axle, it will run into the same interference issues as the corvette trans.

Oh, just for laughs and trivia Ultramaroon, there's a company that makes upside-down Porsche transaxles specifically for putting them behind the engine...
http://www.patrickmotorsports.com/pa...-transmission/
EDIT: strike that about the 944 gearbox, the box appears to be behind the axle. Could work, worth looking in to.

[Crazy Drew]

Not to be a **** but I still think you're overlooking the complexity of building the torque tube, regardless of what trans you do. The alignment of this must be spot on to prevent excessive angular change in the driveshaft that will cause vibration. Most torque tube cars I've seen (correct me if I'm wrong) use guibos that have very minimal acceptable angles of deflection. In addition to this you're now talking about linking the front and back of the drivetrain with a structural member with a stiffness different than the car itself... I have in my life worked on 2 c5's with bent driveshafts from wheel hop and both exhibited excessive vibration at highway speeds due to this however when checked out by a driveshaft shop they deemed it "acceptable" runout. The only thing that resolved the vibration was a brand new driveshaft from GM.

This IMO is your largest hurdle, in addition to the fact you'll somehow need to come up with the flanges/bellhousings to attach the torque tube.

One last thought, how would you support the driveshaft in the tube at the motor? The pilot bearing?

[Ultramaroon]

Originally Posted by Spartarus

Oh, just for laughs and trivia Ultramaroon, there's a company that makes upside-down Porsche transaxles specifically for putting them behind the engine...
http://www.patrickmotorsports.com/pa...-transmission/

Hey, that's cool. Who would've thunk it?