I have an ITR motor I'm rebuilding, and I'm shooting for ~400whp on E85. I planned on keeping the ITR manifold for as long as possible, since I prefer its mid-range power delivery over the Edelbrock manifold.

However, for my next, NEXT build (), I plan on upgrading to a GT3076R and maxing it out at ~550whp.

When is it absolutely necessary to upgrade to the bigger intake manifolds (Edelbrock, Full-Race, etc)?

Post up high-HP dyno plots with Skunk2 or ITR intake manifolds if possible.

 

If you are looking for efficient power I'd say an ITR IM is good until 300 whp, at which point you're either running an AEBS (I am told Skank2 PRO is equivalent) which you should probably already be running, or looking at making big power with an Edelbrock Vickie-X. That doesn't mean you can't go interesting places with an ITR IM; just remember racegas makes up for lowered knock limit.

84mm ITR, Precision SC44, 26 psi:



84.5mm GSR, ITR head and IM, .60 trim T3/T04E with stage 5 .63 AR turbine:

(same car and owner, diff bottom end and different-yet-equivalent turbo)



Same car with a hundred shot - the power abruptly falling off @ 7500 rpm was due to the turbine being a restriction, nothing wrong with the IM :