Here's the test rig in its entirety. I did some testing, but before I go into detail, I'll list some limitations of the test fixture.
-It is not bolted to an engine block, and I'd guess that the engine provides some support to the case
-This jig simulates 100% traction with an infinitely heavy car (it holds all output shafts completely rigid).
Now with that out of the way... HOLY CRAP, the "theory" of case flex is now a law. This thing isn't just kind of weak, I was really surprised by my findings. I'll have a full write up with the release of the reinforcements as I don't want to make a blue print of exactly how somebody else should build a competing reinforcement right away.
I measured changes of dimension at 7 different spots on the case. One data set was recorded at 230ft/lbs, and a second data set at 300ft/lbs. At stock torque
(230ft. lbs continuous load) with 3rd gear engaged, I measured a peak dimensional change of .003" at one spot of the case in relation to the bellhousing. That doesn't sound like much, but the 5mt's gear lash spec is .006" with a tolerance of +/-.001"
. What this means is that the gears are potentially moving beyond their recommended clearance range even at stock power, they're most certainly wildly beyond the recommended tolerance during a launch or hard shift. I stopped at 300 ft/lbs... The input shaft was twisting so much that I feared for my spare transmission's safety. Remember that this data was recorded with the output shafts completely bound up.
Another interesting tidbit that confirms input shaft flex... At 230 ft/lbs, the shaft twists at least 5 degrees at the clutch in relation to 3rd gear... In other words, with the gear locked in place, the clutch disc is about 5 degrees of rotation ahead of the gear... Think of the swirl pattern on a candy cane. At 300 ft/lbs of input torque the input shaft had moved to about 10 degrees of twist... scary.
Furthermore, I understand that my test results may be hard to take seriously since I have a clear incentive to make the case sound weak (being that I want to build a product to reduce flex), so I will have video of the test up on my website once the reinforcements are ready for production... This way all of you folks can watch the needle on my dial gauge go nuts every time I lean on that torque wrench