I have a 68mm throttle body which converts to 2.67" (flows 750 CFM, more than the F&B 70mm). So I use that as my "bottle neck". I want to avoid going any smaller than that. So 3" intake tubing fits the bill. I want an air box so I can avoid an open air filter just sucking in hot engine compartment air. Every 10° drop in intake air is +1% HP. So if inside engine area is 100° and outside air temp is 60° that's +4% which on a 300 HP engine is 12 HP. I almost went with an air filter sticking out of the hood because it's not a DD, but decided against it. Here are pics.
Opening of the stock air box is now 3" x 4". It has a drop in K&N air filter. The same panel filter in the similar year TJ is nearly identical dimensions and flows 661 CFM. The stock replacement drop in panel filter from K&N for the 2010 Camaro SS 6.2L only flows 588 CFM!! And that car makes over 320 REAR wheel HP (picks up 8 HP going from stock paper to K&N). As you can see I use all 3" tubing. The stock tubing coming off of the air box lid is 3" and so on. What you can't see is I also swiss cheesed the whole front fascia and headlight bucket (with a hole saw) behind the headlight, and removed the flat sheet metal that sits in front of the airbox intake and behind the headlight. I tried to allow as much cool air to reach it as possible short of fabricating a hood scoop. I'll add a picture of one other little touch....
Behind those 3 holes I cut the lip off of the hood to allow good air flow. It doesn't really shoot straight at the intake or anything. It might help, but I like how it looks so there's that.
I think this intake can support more power than I'll make, which was my goal (without getting too crazy). It is cheap and easy. I also have a 1" throttle body spacer in there. If anyone is interested I can actually put up a parts list and a sort of how-to. It's not super fancy because I don't think it needs to be. A lot of research and common sense went into this. I think it errors heavily on the side of value. The other upside is it utilizes the stock mounting system and allows use of the stock valve cover vent pcv system.
