I want to fab my own CAI. I will use pvc pipe, and a K&N filter. I have a '96 Ram, with the 5.9 engine. I will be doing other mods in the future.

What size pipe (diameter), and filters are used with the better CAI systems? I'm sure many of you have these systems, could you tell me the size used?

Is 3 1/2" tubing good? Would 4", or 5" be better, or just overkill? I'd like to run the pipe between the radiator, and rad support, to put it behind the grill, and out of the engine compartment. 3 1/2" pipe would be easiest, and there are many 3 1/2" i.d. flange K&N filters to choose from. Any suggestions on how many square inches of filtration element to look for in the filter?

I realize "bigger is better", but there's a limit to what will fit easily, due to clearance issues. But, if I'm going to build my own, I don't want to "under build" it.

Also, is it bad to have the filter exposed to rain? I doubt it's bad for the filter, but how much water will be sucked into the intake? Should I put a "shield" in front of it? Motorcycles with these filters are ridden in the rain, and it doesn't seem to bother them.

Thanks for any info, or advice you can give me.