Let's run a couple of numbers.

Max Mazda e-shaft size is about 1.7 inches diameter.

Formula (Roark) for max stress is = (2 * T) / (pi * r^3)

T is in inch pounds. r is in inches.
pi = 3.1416
Stress is in psi

Figure max stress at 200,000 psi for real good material.

So 200,000 psi = (2 * T) / (pi * r^3)

So 200,000 psi  * pi * r^3 = 2 * T

T = (200,000 psi * pi * r^3 )/2

Radius of shaft r is .85 therefore  r^3  is .614

So max torque at 200K psi is 193,000 inch pounds or 16,000 ft pounds!

Am I missing something or did I add this up wrong??

Hey this might not be such a dumb idea after all. 

No wonder the Mazda rotary shaft is so bullet proof.

Course there is no bending here and fatique considerations
are aside. Even if you took max stress to be 50,000 psi
for good fatique max torque would then be about 4000 foot pounds. 
Figure 500 ft pounds torque per rotor (turbo) for a eight 
rotor engine. 

Not so far fetched. All you need do is figure out how to 
put it together.

Paul Lamar
 
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