I want to replace my 4lb with a 6lb but I want to open the exhaust before I do it. I was going to get some dynatechs LT headers when I asked this question ........

since 2 Magnaflow 2.5" cats replace all 4 factory cats wouldnt that open the exhaust system enough reducing heat build up at the head to handle a 6lb pulley with a ported eaton since the biggest "exhaust restriction/heat build up" is the factory cats ??

I ask because 2 Magnaflow cats are about 200$
and the dynatechs are 1295$..

 

Go with the Kooks long tubes for 800 and the bassani off road cats for 250. Thats still under 1250.

 

I think that up to 500 rwhp the stock manifolds with hi-flow cats and the magnaflow 2.5 X 2 in and 2.5 X 2 out with the built-in pressurized X is probably your best bang for the buck up to aforementioned hp rateing. The 4 stockcats are the biggest choker in the stock system. But, if in the future you plan on stepping up the power, bite the bullet and get the full system that includes the cats and mids.