a header and a manifold are definitely not the same thing....even the h22a manifold which is designed like a header, yet is still a manifold, is inferior.....most manifolds are better for emissions while headers make better power, and headers scavenge a LOT better than manifolds.....that might not sound like lot, but read up on scavenging....poor scavenging means your old, burnt mixture is staying in the cylinder and mixing with the new mixture, therefore hurting power a lot....headers help get all that shit out and allow each cylinder to work more individually as opposed to the manifold setup....same goes for turbo setups....small power works well with manifolds, but to make big efficient power, you'll need an equal length tube header