| Say *an* NA with some mods is making 240FWHP@210ft/lbs of TQ. I believe the stroke is ~3.2". 3.2" / 2 = 1.6" <-- This is the distance of the center of the connecting rod journal to the center of the main crankshaft journal (axis of rotation) 12" = 1 foot
so
12" / 1.6" = 7.5 <--- This number represents the factor that will convert our ft/lbs at the flywheel into actual pressure load at the connecting rod journal. So, 210 ft/lbs of torque is generated when 210*7.5 lbs of force is applied to the connecting rod journal. That number is: 210 * 7.5 = 1575lbs.
or ~3/4 of a ton. Now imagine your crankshaft with half of your Z hanging from a connecting rod journal that is horizontally placed from the axis of rotation and with the crankshaft securely bolted by the flywheel bolt holes and kept from rotating. 1575lbs of weight on the connecting rod journal is going to produce very apparent 'twisting' of the crankshaft. Imagine this happening at 7200RPM where pistons are going up and down 120 times a second, 3 cylinders firing every rotation of the crank for a total of 360Hz (120/s * 3). The harmonics of this generate higher order frequencies that cause the crankshaft to vibrate. This tortional loading is why a tortional vibration dampener exists. They are commonly referred to as a 'harmonic balancer', but that name gives a false impression that it has something to do with static/dynamic rotational balance, which it does not. It is a harmonic balancer; i.e. it balances the harmonics of the crankshaft - it is not a component that balances the weighting of the rotating assembly and plays a funny sounding tune (harmonic balancer). ;-) While 1500lbs of weight on the crankshaft sounds like a lot, in comparison to some more impressive power numbers it is childsplay. Remember that factor of 7.5? Consider this: GT2530's can make ~550RWHP. That's about 630 crank horsepower. Lets say that at its peak, it makes 570ft/lbs of torque at the flywheel. 570 * 7.5 = 4275lbs of force on the connecting rod journal. Over two tons of weight bearing down on the crankshaft. THAT will definately cause some crankshaft ringing. :) (*My figures may be slightly incorrect because I cannot for the life of me remember what the exact stroke is on our engines. But I believe 3.2" is close enough to demonstrate what's going on in there. :) )
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[ agpowers@bellsouth.net ] [ Zemulator Information Sheet ] When pigs dance, you better get it on video... "You never really learn to swear until you learn to drive."
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06:19:42 01/03/03
