I did some searching and it seems that the exhaust manifold is a bottleneck in the sequential system (if I am wrong let me know). Does anyone make an upgraded sequential exhaust manifold? I couldn't find anything after searching the forum. Would it have to be custom made? Can it even be done? Thanks for the help.

 

The exhaust manifold is the ultimate bottleneck in the exhaust tract. Mind you, it's not the first restriction you'll run into as you start modding the car. In fact, it's one of the very last restrictions you'll meet head-on. Could you design a better flowing replacement, sure. Is it cost-effective, probably not. If you reach the point where you're maxing out the exh manifold, and you have nowhere else to go, it's time to take the next step up.