L31MaxExpress
I'm Awesome
I get 20 to 21.5 pretty consistently with my 91 RCSB K1500. Its a 350 with a HM290, 3.73's and 265/75-16s. I started with a 97 vortec block and TBI heads with the stock roller cam. I used split ratio roller rockers. 1.6 intake and 1.5 exhaust in an attempt to gain more low end torgue to reduce downshifts in the mountains. I'm running a 180 deg thermostat to keep the fan clutch from engaging as often. I have an edlebrock intake with JBL shorty headers and Y-pipe through a single 3 inch pipe and muffler ending before the rear axle. I wanted to reduce back pressure to reduce pumping loss. I have a 14X4 inch open air filter. I also used the old style intake gaskets to block off the heat exchanger under the intake. I installed the coolant block off plates in these gaskets for the rear coolant passage. My tires are Goodyear dura tracs in load range E and I run them at 85 PSI to reduce rolling resistance. I'm running a custom chip from Harris. I explained to him MPG was the main goal and I would be thrilled if it made 180 HP. I have other trucks for towing and hauling so crazy power isn't important here. I also run Mobil 1 5W-30 along with synthetics in the axles. I replaced the leaf spring bushings and all 4 front control arms along with all steering parts before a 4 wheel alignment. I wanted to run as straight as possible to reduce drag. If the front leaf spring bushing are wore the rear axle can shift to one side allowing the truck to YAW like a forklift. This will plow the wind on one side and create a vacuum on the other. That condition will increase wind drag. I haven't found a smoking gun for MPG just a lot of little improvements to get the mileage up.
The only smoking gun I have found that helps consistently in good weather conditions, flat road or downhill is highway lean cruise.