Squirrelly McNuts
Newbie
I'd love to see some data to back that up other than the dyno sheets from K&N themselves which are almost certainly fudged a little. Regardless, the factory intakes on these trucks (especially the K47 boxes on the Vortec trucks) flow more than enough for all but extremely heavily modified engines. I'm not sure about the TBI intakes as I've never owned one, but I'd imagine they're sufficient. My statement about Volant or nothing still applies though, they're the only company with a proper closed box design even for the TBIs that I'm aware of.
Also I completely missed the original topic of this post, which stated you were working with a TBI, and trying to go TPI. I just saw the programmer and CAI bit and had to chime in, I apologize! @pro17's posts are probably the best info you're going to get here.
df2x4 I don't mined talking about this at all (as long as it stays civil). While it may not be directly on topic it is directly related. Now I am going to preface what I am about to say with I am NOT an expert. However I am very well read on this particular topic. I fined it very fascinating.
First I do not have on hand a dyno sheet to point to for comparable data (If I do fined one I will let you know. I will be looking). However both "Hot Rod" and "Four Wheeler" magazines have done several articles on the topic with dyno testing. I am certin others have as well I just have not read them. While I don't think either has done K&N specifically, they have done very similar kits. All the reading I have done on the subject boils down to faster air makes for crisper throttler response, SOME HP at the top end (depending on the engine and other mods involved), and in some cases MPG gains.
Second you are correct a good late model style intake will breath well enough to not hinder the engine, even a mildly modified one. However that dose not mean it is Ideal. Factory systems are built based on packaging, expense to make and ease of installation. Most factory air systems have at least one 90% bend in them and any article from a reputable source will tell you the least amount of bends and the grater the angle of thous bends, the faster the air, the better. Most after market air intake systems are marketed as "cold air" only because it is the buzz word that a non car person is going to look for. Most just rout the air better with less 90% bends and a pod filter to make them look cool but better angles are better angles. You could just as easily use the stock air box and re-plum the piping to be smoother and more direct. Achieving just as good if not better results.
Lastly what I can point you to is an episode of "Engine Masters" -->
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While they do not test an modern style "Snorkel" systems. There is a lot of good dyno proven results that give you the basics of what to look for in a good air intake system.