In another thread i was talking about the difference in mileage and performance my van gained, just by removing the secondary cat converter, replacing muffler with hi-flow unit and all piping with 2.5" inside diameter saved me $40 in fuel round trip to Tacoma Washington from Portland Oregon, last month the van used $60 up and $40 back because it's downhill going back to Portland, the work was done to the exhaust and i made a identical trip this month and used $60 round trip, that's pretty substantial to me and worth every dollar i poured into the exhaust..
Tacoma to Portland is downhill ? They're both at or near sea level. Or rather Portland is further from the ocean than Tacoma is, that would make it slightly uphill.
You're probably right, for some reason i always associate north with uphill, makes sense to me anyways
But the van runs so much better and every modification i have made so far has been noticeable improvement, very pleased with it..