I've owned my CTD for almost four years, and haven't done much yet to increase its performance. However, it's about time to do it! I have a '97 2500 4x4 auto; the intake manifold has an EGR valve that I think is specific to California. I recall reading or hearing somewhere that there is a difference between these EGR-equipped intake manifolds and the non-EGR manifolds--that the non-EGR manifolds have a larger air passage and therefore allow for better "breathing. " Is this correct? If so, would it be advisable to replace my current manifold with a non-EGR manifold? And finally, where might I find one?