The amplitudes of the torsional vibrations to increase with the power output. Dampening is very specific to the engine and the application for which it is being used..
The angular displacement of the of the crank is dependent on the force and frequency of the excitation. Angular displacement and natural frequency of the crank go hand and hand. You can have a heavily boosted engine that will stress the crank, but its the firing frequency that is a must know and the natural frequency of the crank. If the firing frequency lines up with the cranks natural frequency, then the component will be short lived. The tuned dampers are designed to help dampen out or shift the cranks natural frequency . When increasing the cylinder pressure you increase the amplitude of the frequency. When we look at torsional data, it is order tracks we plot it in. A order is what happens every revolution of the crank, on a four cylinder a 2nd order is a firing order. When you change rods or pistons you change the natural frequency of the crank, you may shift it rite into the firing frequency. The polar moment of inerta is also changed, by changing pistons and rods.
One thing in common about the turbo engines that you mentioned Red, is that they are a factory designed and built turbo engine. The hyundai wasn't designed to deal with the turbo. Most four cylinders do not require a damper in stock form, some do have a elastomer damper that helps dampen some resonant vibration, but is not designed for any increased amplitudes. The four cylinder cranks are relatively stiff, due to there short length and small displacement.
I can’t say for 100% percent that you will need a new damper, I have never done any testing on a Hyundai four cylinder. It may live for 200,000 miles, but then again it may live for 2,000 miles, it’s a unknown for me. Sometimes torsional vibration won’t always break a crank, but you may see excessive wear in the oil pump, transmission, broke valve springs, and etc. The amplitude of the resonant vibration is what kills in a short amount of time.
To conclude, the severity of torsional vibrations and shear stresses caused by torsional vibration depends on many parameters: operating speed, torsional natural frequencies, lateral natural frequencies and mode shapes of the shaft system, system damping characteristics, and any excitation frequencies produced by torque fluctuations. To add here I am considering taking some torsional measurements on a hyundai four cylinder, a friend of mine from work has a copy of MatLab with the Hilbert Transform, if I can get a hold of DAT recorder I may be able to get it done. It will take some time though.
I have enclosed a link that has some torsional pictures and how a torsional pickup is setup.
http://photos.yahoo.com/bc/tiburontropic/lst?.dir=/Torsionals
Edited by - HRD_Tiburon on 02/01/2002 9:58:28 PM