"The horsepower curve is pretty steep at the lower rpms, so I think that the
horsepower available at the 1500rpm minus 31%, even with a 3.73 rear axle ratio, is low enough to seriously lug the engine."

My '85, with a manual transmission, will protest if I try to engage the overdrive at less than 2000rpm. The automatic transmission has a taller overdrive gear (0.69:1), but because of the shorter rear axle the end result is that the reduction ratios are about the same. I think. :-)


"The old original overdrive units, my family had one on our 1950 Mercury, was
a manually engaged (T-handle under dash) and had free-wheeling. When you
backed off on the gas, you were in neutral, coasting along. Aah, technology!"

Never driven an automatic Volvo, but have noticed in other automatic cars that the tach drops to around 1000rpm if one backs off the gas at speed. I guess that must be the stall speed of the convertor?