a guy i work with has done lots of custom work on DSMs and come custom work on an 11 second corvette, so i think he knows what hes doing. were currently working on a custom intake manifold for my camaro. were going to take the manifold and the lower plenum, P&P it quite a bit, and weld on a 3" Y-shaped pipe to the throttle body. itll look a lot like the 3.4 intake plenum. do any of you with custom work think that 3" pipes to the plenum will be too much? were going to use the stock throttle body mount for now, but ported out quite a bit and later switch over to a bigger throttle body. is it a good idea?

 

Air flow dynamics and CFM by RPM will tell you what size you need.
However, just off the top of my head 3" should be ok. You figure that ios roughly the size of 3 intake ports' volume.
I think it would start to be a restriction around 7K or so.

 

speaking of custom intake manifolds anybody kno what is up with trueleo's intake and alans custom intake?