I'm looking to make a custom header for my RX. 4port N/A 13B. Reguarless, they'll be tuned. My questions are...

What are the differences in a long a short primary system? I'd like to have a long primary system, but I need to run a catalytic converter (as far as any inspection station can tell at a glance anyway) and from what I understand, the collector would be somewhere near the rear axle.

Also, Does anyone happen to have the formulas for each?