Well thanks to Rodger and Dave I got to do a little "fun experiment" again today. I live on a black top two lane branch of what was once Route "1" back in the early 1800 era. Now it is just a backwoods branch parallel to U.S. Route 1 but a nice test run for about a 1.5 mile stretch. Holding my 700R4 in second gear (Lokar second) and putting the pedal to the fiberglass the shift point from low to second occurs at about 3100 rpm. Holding the trans in just low gear allowed the engine to go easily to about 3700 rpm so the shift point is somewhere around 3000 rpm. More gentle acceleration showed a shift point from low to second around 2500 rpm. Thus OD kick in holds the rpm down around 2000 rpm in "normal" driving. I recall reading about the OD 4th gear automatic down shift having a lower limit of about 1900 rpm and I have the automatic electronic shifter so I guess the pressure shifts are set just above where the minimum kick-in for the OD occurs. As long as the OD doesm't slip I think it is good that I can cruise at only 2000 rpm for economy and engine life. I only see the tach go over 2100 rpm while cruising at 55-60 mph but I can get it to go up if I punch the throttle but then it settles down once the speed stabilizes. I guess this has something to do with the torque convertor but I see the same thing on both my 1998 Sunfire and my 2008 Impala and they both have 4-speed auto trans with similar gear ratios.
Don Shillady
Retired Scientist/teen rodder