Cowl or Ram Air Intake

[MMcCallie]

I've been without my truck for months this spring and have been imagining some sort of intake to allow and perhaps force cold air into my air filter. My engine runs hot, is a tight fit in my Ford. I've asked a few folks for their opinions of what would work better, having an intake with the opening facing the front of the truck at the edge of the hood, or facing the windshield right in front of the cowl.

I have yet to mock up some sort of testing device to mount to the hood and see which way there is more current in what location. From what I've read, a ram air intake must reach as far forward as the grill or the air will flow over it. A cowl scoop must be close to the windshield to receive the vacuum created via the Bernoulli Principle.

On a carbureted gasoline engine ram air can cause problems because too much air will affect the A/F ratio and cause the engine to stumble. Obviously not a problem with a turbo diesel because the more cold, dense air we can compress into the intake to spool the compressor side of the turbo, the better.

I do a mix of driving from stop and go city traffic to hundreds of miles on the interstate without stopping from elevations of sea level to 13,000'. I want improvement in fuel economy, spool up, cooler coolant and EGTs, less smoke and more power.

I am using a True Flow XDI intake that points straight toward the passenger side fender. I am sticking with this intake as it is the only one that will handle the harsh off road environments I put my truck through. I envision a right angled box or tube that will take up the few inches of space to the fender and seal against the filter. Possibly something flexible to keep it connected to the hood mounted scoop when the hood is raised and lowered, or something that will just seal tightly when the hood comes down. I plan to have some sort of drainage holes for water to escape where the tubing bends just before the filter, and a screen or grill of some sort right at the opening of the scoop, possibly a small filter.

If I mount the scoop facing the cowl, it will be easy to add a snorkel which would be nice on dusty Jeep trails that would run up along the A-pillar. Can't go through the fender, I'll crush it on a rock or tree off road. If I build a ram air intake, the pipe will probably need to be at least 4" in diameter and will have to extend all the way down to the front of the hood. What I need to know is which is more powerful, the ram air effect at various cruising speeds, or the vacuum effect at the back of the hood though it will be several inches in front of the windshield so it doesn't hit when the hood is open? Anyone have experience with these intakes or know which would be more beneficial for my rig?