CAI sizing go larger or smaller?

[bob442]

Hey everyone, been a while since i've even thought about my 60*, i finally got around to making my own adaptor plate for the 65MM TB from the 3.4DOHC (which is the same as a 3.5 DOHC TB) so now that i've done some slight port work to the upper intake and blended the TB opening, i'm going to have to build a proper CAI. the current one on there is some random pipe i found at the wrecker and its actually 2.5" in diameter. the out side diameter of the TB is 3 1/4, so i'm wondering if i should go with a 3 1/2 or 4" intake tubing. Why do i ask? the whole "Venturi effect" http://en.wikipedia.org/wiki/Venturi_effect
So should i go greatly oversized? And also aside PVC has anyone come up with other good idea's for materials? i'm thinking i might have to make it out of exhaust tubing...

[bob442]

Is it that much of a dumb question to get answered...?

[Superdave]

I've used exhaust tubing for a long time, you can get mandrel bends for fairly cheap and then weld it all together, wrap it in header wrap and have a very nice system. Of course it weighs more than an aluminum system would but the final product looks better. Either way, check Ebay for mandrel bends

I'd use 3" on your engine, going larger than that is not needed for most engines.

[AleroB888]

I believe the inlet/outlet shape, diameter, length, and bending radius of the tubing all come into play, especially between the TB and the MAF sensor. It is easy to flare or taper exhaust tubing if needed, not so easy with aluminum. 3 inch tubing works good for me from TB to MAF. I would pay particular attention to the areas of transition at MAF sensor to pipe to TB, and assume there will be at least some venturi effect. Out to the CAI, I would go as large as is practical.