Rich, you asked about where "flex" is built into the system to accomodate manufacturer variences and tolerances, as well as drive train movement...

I'll try to keep this simple

1. Lift your hood
2. push sideways on you engine and observe how much it moves (its mounted on rubber bushings)
3. start your car while on a lift and have someone rev the gas while looking underneath at the whole drive train from engine to differential

the trans and diff are also mounted on rubber bushings (unless you have upgraded yo poly bushings, in which case there will be less "flex" but it will still be there)

The entire drivetrain is mounted to the car via flexable bushing so it can move and flex within acceptable tolerances for the power levels it was built at.

there is so much flex built into a stock car that companies like pfadt, ecs, hinson etc., build and offer braces and upgraded bushings to reduce flex, as increasing power levels can cause so much flex that it can break stuff, but even these upgraded systems still have flex built into them, as no flex at all causes stuff to break.

so, too little flex and stuff breaks, too much flex created by high power levels causes stuff to break, leaving a drivetrain unbolted together while getting into the skinny pedal on an LME built 427 twin turbo setup....., yep, you guessed it, causes stuff to break....the 3 or so millimeters of extra length on the driveshaft on each end for your application would more than easliy be absorbed by the continual flex of the drivetrain system, even if you have upgraded bushings, mounts, etc..

so, the whole drivetrain system is mounted to the car on flexible bushings that allow several inches of play front to back...both ends being pushed a few millimeters apart by this driveshaft is well within the movement tolerances of the drivetrain, that regularly moves several inches all on its own (compressing the engine and transmission together, as well as torquing and twisting) in stock configuration.

In fact, where people break stuff like drive shafts, is when they do things like put in solid, nonflexible metal Guibo's that CANNOT flex, and then you break stuff (or alternately, you don't bolt you drive train back together then run 800+ hp through it )

Jarek, when making the flex plates, be sure to make them in a way that they can flex slightly, this is why the ***** flex plates are made from a steel that can flex and why they have thinner areas alternating with thicker areas...not too complicated but important.

Back to Rich....The whole drivetrain is designed to move and flex and handle small part size variances and movement, however, if one wanted to be extra safe, and remove some material to make a better custom fit, then you don't remove material from the drive shaft, as this would compromise its structural integrity. Where the shafts mount to the shafts on the car there is 12-15 millimeters of material at the connection points where everything bolts together, 2-3 millimeters of material can be carefully removed from each end (front and back of car), without compromising enough torsional strength to matter on anything under 2000 ft lbs of torque.

if you are over 2000 ft lbs of torque you need all custom machined parts anyway, and you will still break stuff, thats just how it is with REALLY big HP/Torque apps.

Hope this helps :-)

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