hotrod wrote:David :
Which axis orientation, and what specifically are you looking for?
Lateral motion from torque reactions or vertical motion from broken engine mounts and chassis flex, or can you see vibration generated by detonation, or misfire?
Larry
Typically, engines will rotate with torque which will be resisted by the engine mounts. Oil soaked rubber mounts will allow excessive movement as will mounts that are too soft for the torque forces. The mounts were designed for stock engines.
But engines also move vertically due to imbalance issues which must also be absorbed by the damping effects of motor mounts.
Racers will sometimes use solid motor (or trans) mounts, which then transfers vibrations into the frame or chassis. Now the whole car shakes, rattles and rolls.
Random misfires do not usually present sufficient amplitude for accurate measurement. A dead cylinder is another matter and would be obvious.
The fundamental frequencies produced by detonation are on the order of 5-7kHz and might require a more accurate accelerometer. They are called knock sensors. Separating the knock signal from other engine noise can be a problem but there are techniques and methods which can be used.
Engine vibrations are usually present as orders of engine speed. At 6000 rpm, which is 100Hz, we would expect to see vibration peaks at 200,300,400Hz, etc.
Most data loggers don't do a very good job of data analysis. But many allow collected data to be exported into an Excel spreadsheet where data analysis becomes unlimited.
Please send pictures and contact information.
