grab a spare bottle for a grill, then get an adjustable regulator from Ace harware (in the propane grill accesories isle) they have a heater buddy brand one that goes from 0-40psi. Then hook it to a good 0-15psi gauge and adjust the regulator for 1.5psi or thereabouts (experiment) Then run a line to the air filter and be careful
if you're afraid of it getting left on by an ooops moment add an electric solenoid and a pressure switch so that it will only come on with 2-3psi of boost pressure (or whatever setting you choose)
You'll have to tinker a bit and experiment, but you can get good results just by being resourceful. BTW, a normal grill regulator is 1/2psi and doesn't really put out enough to be worth while.
Any more question, feel free to ask.
A price breakdown is as follows:
Regulator $40
gauge $25
Hoses $15
Bottle $free if you have it around
If you want to add a solenoid for mounting the tank outside the truck (my way was with it sitting in the passenger floorboard while I experimented) then add to the cost
Air solenoid $20
pressure switch $15
So there you have it, a good setup for less than the cost of a full tank of fuel that should net you around 2-3 mpg depending on your setup of course.
George
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1997 2500 ext cab long bed 4x4 Boost control elbow, KDP tabbed, silncer ring MIA, Z-series gauges, 47RE built w/valve body & converter, #100 plate.