Limitations of 2.5" Intake Piping vs. 3"
 

So, I've noticed that most people use 3" intakes for their "cold-air" setups. I'm planning on on fabricating my own CAI for my supercharged FC particularly because my underhood temps get ridiculous with the extra heat of the supercharger. I've found some 2.5" (internal diameter) tubing that should work really well; however, I'm concerned that it might be too small, and therefore restrictive. In thinking about this, I thought about my FD which uses 2.5" diameter IC piping and has no problems. I don't know if that's significant, but it is interesting. Anyways, I know how to calculate the area of the circle. 2.5" v. 3" has an internal area of 4.9 square inches and 7 square inches respectively. Looking at the issue that way, it seems that the step up to 3" is significant. Does anyone have any hard numbers as to why I shouldn't use 2.5" tubing? Doesn't the AFM go down to 2.5" on the engine side anyways?

Thanks for the input.

I'd just stick with the same diameter as your inlet for the charger.

i am making a intake for my t2 and am using either 2.5'' or 3'' piping as long as it's the same size or bigger piping as your superchargers inlet it shouln't restrict air

The bigger the pipe is, the less work the engine has to do to suck in air at a certain rate. The less work the engine has to do sucking (and blowing), the more power you get at the wheels. For intake pipeworks it's as simple as that. The actual power difference will depend on all the other restrictions the engine has to overcome, but the bottom line is if you reduce or remove a restriction you will get more power out the back. Fit the biggest pipe you can fit.