Just curious, does anyone know how many rpm's a non turbo 740 or 940 will be spinning at 70 mph? My turbo 940 was doing 3,000 rpm. They both have a 3:73 rear end so just wondering how much the rpm's drop when the torque converter locks up?

 

the RPM 'slop' in the torque converter varies with how much throttle and load. its pretty close to zero on level ground cruising at a steady speed with a very light touch on the throttle. its a fair bit more with a heavy load climbing a steep grade where you need a fair bit of throttle.

 

Don't quite understand. Are you saying, when cruising, on level ground, both engines will be at 3,000 rpm's? If so, how can that be? Locking torque converters act like another overdrive, do they not?

 

When the torque converter locks up it only drops the rpm by 200-300 . I'll have to check my 740 at 70 mph as I don't recall the rpm at that speed.

 

Would like to know. Thanks

 

cruise at a steady 70 MPH in overdrive on a flat straight highway with no significant headwinds.... gently feather the throttle til you're just barely slowing down, and note the RPMs.. now increase the throttle until you're gently accelerating back to 70, and note the RPMs. the lockup RPM will be in between these two.

 

I just was out on local roads and at 60 mph my tach was at 2300 rpm. At 55 mph it was at 2100 rpm. Couldn't hit 70 on local roads.

 

As I thought, that's about a 300 rpm decrease. My turbo is around 2600 at 60 mph. Thanks for the confirmation. Wondering about this in my search for increasing gas mileage to a respectable amount, considering the size of the engine. I threw in a 3:31 rear end and axle from an early 960 wagon, which dropped rpms from 3000 to 2500 at 70 mph. If I throw in an AW71L that should drop it down to 2200 rpms and should get the highways mpg's up near 30. I hope. THANKS