T-5 Tranny conversions? - Page 10 - Alfa Romeo Bulletin Board & Forums
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post #136 of 136 (permalink) Old 03-27-2015, 07:57 AM
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Some folks need to do some homework on the subject of the 'critical speed' of shafts. Aluminium and carbon composite driveshafts have a higher stiffness to weight ratio than steel, and thus can be designed to have a higher critical speed at any given length than a steel one.
Therefore--it is possible to replace a two piece steel shaft with a one piece in aluminium.
If you reach, or even approach the critical speed (the speed where it whips like a jump rope) of a drive shaft, EXTREMELY ugly (even fugly !!) things can and WILL happen.
If ujoints or support bearings absorbed ANY significant amount of power, they would get unGodly hot !! Just 1 Hp worth of friction generates 2546 Btu/hr. of heat--MORE than enough to get either a U joint or a support bearing WAY hot !! They don't--so--they are NOT absorbing that kind of power.
Im pretty well convinced that Alfa used the guibo in their driveline for two reasons: (1) to get a CV joint at the first joint in the two piece driveline. (2)to provide some torsional shock absorbtion in the driveline so as to make life gentler for a tranny and final drive which are not excessively stout. Shock loadings absolutely produce the highest losds on transmission and final drive gears.
Another issue with guibos, which becomes obvious in racing, is centrifugal expansion (and occasional failure !!) at high rotational speeds.
One more thing while I'm on a roll: Dana Spicer, for one, says NEVER to set driveshafts up so that their U joints are running, steady state, at a deflection angle of LESS than about 1.5 degrees!! This much deflection is necessary in order to move the needles in the joint far enough so that they (1) lubricate themselves (2) do not brinnell themselves into the cross and caps.
IMO spending money for time on an inertial (NON load bearing) dyno is an absolute waste. To quote RJ--'the numbers they generate are crapola !!'
Greg
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