Ideal cruising rpm

[Big Sugar]

So. Im going to setting up my 66 charger for the 2014 power tour, my plan is to swap in a A518 tranny behind my 6 pack 440 as opposed to going with the GV unit.   

With my 3.91 gears ill be turning 2135 rpm at 65 with the new OD A518
             3.55 gears ill be turning 1948 rpm at 65.  "     "     "     
             3.23 gears.           "       1764     ".    65.        "                       

The motor is pretty torquey down low , but i don't need it to be lugging while cruising , should  i chart my engines vacuum curve to determine the sweet spot to bring the rpm gearing down into ?



Ron
                                   

[Cooter]

Ron, all this is kinda dependent on your camshaft specs as to where your cruise RPM should be. You state you don't want it lugging, but if it's below the camshafts power band, then that's exactly what it will be doing.

[elacruze]

Charting the vacuum is a very good start, however remember that the vacuum will change with load and gearing. I have a GV with 3.55s which gives me 2700@75mph. I got a trip average of 15.6 over 3100 miles on this year's PT with two tanks over 23mpg.

Another seat-of-the-pants way to find your sweet spot is, 'where does this damn thing ping that I can't seem to tune out?'. If you find yourself with part-throttle pinging somewhere between 2000 and 3000 rpm, that's the place your engine is making the most dynamic compression. Of course, your timing curve plays into that but you can plot the timing curve, vacuum curve (manifold pressure) and ping RPM to get a solid starting place.

[elacruze]

oh and get a Rostra Cruise Control. It will be the best money you ever spent.