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Our 940 runs that RPM at 70. It's the 4.10 rear axle which causes that relatively high RPM. Later 240 automatics had a 3.73 axle (as did 940 turbos), and their tires were slightly larger in diameter than the 195/60-15 that you find on many 940's, so they would run at lower highway RPM. Against that is the 240's lack of a lockup-type torque converter on their automatics, so the resulting slippage would raise cruising RPM's a bit. In the end - probably little difference. Fortunately, sound insulation in the 940 is much better than the 240, so just ignore the tach!
Both our 1983 240 and 940 will give 30MPUSG with steady 70mph highway driving. The 83 turns about 2600RPM at 70 with the M46/OD transmission and a 3.31 axle, so the higher speeds of the 940 engine are perhaps offset by its more sophisticated (LH2.4 and EZ-116K) engine management systems.
If your car has EGR, that valve and its actuating vacuum solenoid are failure prone, and that will give higher NOX readings.
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Bob (son's 81-244GL B21F-M46, dtr's 94-940 B230FD, my 83-244DL B23F-M46, 89-745(LT1 V8), 98-S90, 77MGB and four old motorcycles)
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