Quote: the one thing that been eaten at me was the concept that fi was suppose to give better performance and fuel mileage over a carb what gives?? I would love to get alittle more fuel mileage out of my 99 p/u 318 auto. What about installing taller tires wouldn't that help fuel mileage?
The problem is peak fuel efficiency isn't always the cleanest burn. The tailpipe has to put out limited amounts of... whatever comes out the tail pipe, and leaning it out for best mileage can jack that up. Also, it seems to me that the pre-magnum TBI motors got better mileage, but the lean condition led to cracked heads over time. Taller tires should help with cruise mileage if the combo is right, but it'll affect acceleration. Skinnier tires will help with rolling resistance.
tuning for emissions (specifically lower NOx emissions) leads to fuel economy compromises
taller tires might be a wash, because if they have worse rolling resistance, or if they raise the truck up higher, and cause more aerodynamic drag, you'll need slightly more power to maintain the same speed, offsetting dropping the engine RPM.
also, look at the HP/tq ratings of a magnum 318 (230 hp/300 tq) vs. say the 318 out of my 5th ave that got 22-25 highway mpg (140hp, 265 tq)....more power requires more fuel....
1976 Spinnaker White Plymouth Duster, /6 A833OD 1986 Silver/Twilight Blue Chrysler 5th Ave HotRod **SOLD!*** 2011 Toxic Orange Dodge Charger R/T 2017 Grand Cherokee Overland 2014 Jeep Cherokee Latitude (holy crap, my daughter is driving)
