LuLu Posted August 5, 2008 Report Share Posted August 5, 2008 I spent the past 10 days on a road trip with friends, from Chicago to Charleston SC. 988 miles one-way door to door. We took two cars, both Panther frames and very similar in many regards. I was suprised to see such a difference in MPG. Car 1 was Gary's 2003 Mercury Marauder. 4.6L-4V with a mild professional tune, 4R70W tranny and 3:55 gears and TractionLoc. Tires are BFG-KDWS, front is 235/50-18 (32 PSI) and rear is 255/50-18 (30 PSI), exactly what the factory suggests. The Marauder has a front air dam similar to the SGT. 40K miles on the car. Car 2 was my 2008 Mercury Gran Marquis, all factory stock. 4.6L-2V, 4R70W tranny and 2:73 gears, open end. Tires are the same BFG-KDWS, 225/60-16 (35 PSI) on all four corners. No air dam. 20K miles on the car. Gary's not a "hammer lane" lead foot, but I am. Thus he took the point most of the drive. Our cruising speed averaged 80 MPH set by the cruise control, but I took the point on ocassion. Passing through the Smokey Mountains, an interesting development unfolded. On graded inclines and without adjusting his cruise control, Gary would pull away from me to the point I had to click off my OD and add some throttle to stay with him. On the graded declines that followed, I had to click off the cruise control and add brake, or, risk bumping into him. When I was on point, Gary had to brake on the inclines to avoid bumping me and add throttle on the declines to stay with me. There is not a significant weight difference between these cars, less than 200 pounds, not including what the luggage of "significant others" added to the mix. We kicked this around over dinner and concluded that Gary's added HP and TQ pulled his car quicker and easier up the inclines, while my car didn't have such power on tap. Likewise, on the declines, Gary's wider footprint and soft PSI added greater drag than my smaller foot print and higher PSI. CAR 1 MPG...20 MPG overall trip average, no peak available due to older EEC electronics. Car 2 MPG...27 overall trip average, with a peak of 28.2 This suggests that tire size and PSI plays a much more important role in MPG than many suspect. Nice to have wider tires on the pavement when traveling through the mountains, but they come with an added tax in MPG. Before we started this, I suggested to Gary that he bump his PSI a tad, but he preferred to follow factory guidelines. BTW, the Marauder was EPA rated at 17 city and 23 highway MPG. My Gran Marquis was rated likewise. Frankly, I wasn't prepared for such a remarkable difference in MPG, and in my favor as well. Your thoughts? Link to comment Share on other sites More sharing options...
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