For those who have sr20ve's, and are looking to go to the next (allmotor) level, then an upgraded intake manifold might be on the shopping list. While the sr20ve head flows good numbers. the factory intake has a reverse taper to it, which hurts flow at higher rpms, hurting hp.
so here's a bit of a list of available intakes suitable. i've spent a few years researching these, and read a stack of forums posts on the subject. the ideal combination of right runner length, right runner diameter, right throttle body, right plenum volume, right camshaft duration, to catch the helmholtz benefit of overfilling cylinders will drive you nuts. Best practice is to find an intake with no reverse taper, or slight positive taper , ideally 7 inches long , ideally with around the 5 to 5.5cm diameter runners, that perfectly mates to the intake ports of your cylinder head. ideally find yourself a 70mm throttle body or larger. ideally you want around a 18-24 inch intake pipe feeding air to that, at least 3inch in diameter.
There's a lot of talk as to when the standard intake manifold becomes a restriction. if your running standard compression with n1 cams, then read no further, its not going to change much below 7k rpm.
if you want a non trumpet runnered intake, you will want to port the runners/plenum floor like the below example. here's a ported standard sr20ve xcessive plenum.
ported n1 manifold. ugly but very effective. 9+inches, good for mating to an n1 throttlebody. runners do need to be ported, otherwise pretty much zero improvement.
custom xcessive manifold, using standard sr20ve intake base, runners to your spec, xcessive plenum.
n1 xcessive. port your n1 runners, mated to plastic spacer/bellmouths, with xcessive plenum. bellmouths have history of separating under load (me included) 9 1/4 inches long.