Quote:
|
Originally Posted by Brian Carlton
These revs would be applicable with a manual transmission with the rear wheels directly coupled to the engine.
However, in the case of an automatic, with a fluid coupling, the actual rpm at 60 mph is going to be 200-300 higher than 2776, and, hence the posted 3000 rpm figure.
|
It's actually a torque converter. A fluid coupling does not multiply torque. The original four-speed GM Hydramatics from the late forties to sixities had a fluid coupling rather than a torque converter.
Under cruise load a non-lockup torque converter will have some slippage, but I doubt if it's more than about 3 percent, which would only be about 100 revs at 3000. Plus there's some inherent error in the speedo gearing and the speedo and tach head calibration and our ability to accurately interpolate between the hash marks.
If the tach/speedo readings are within three percent of the calculation, then it can be considered okay.
Duke