I know the RMW street header has bigger ports than stock and will match up to a BVH. I compared the stock header to RMW before installation on my Mini.
IT's all about matched stuff.... and that rarely happens if you just buy and bolt. Get huge primaries without flowing enough to fill them, and you just kill torque by reducing scavaging. Get a header designed to improve stuff on a stock head, and it can create just the scenario that Thumper describes.... Make sure that you select parts that will work together as a system, and you can get a lot of improvement. To the question of "all i wanted to know was if the header mod was a reasonable alternative to a full header for the cost" really depends on what you view as reasonable and what your goals are. You'll get a bit of an improvement modding the stocker, but you won't get what you can get with a well designed equal length header that is optimized for your flow levels and peak RPM band. But the difference in price can be well over an order of magnatude.... Matt
I gained power with the RMW header proven on the dyno so I'm pretty happy. It was well worth the money for me. Its a great header with long equal length tubing. Looks, sounds, and performs great!