Originally Posted by
Fabrik8
This often has more to do with the stroke of the engine than the heads. Having smaller ports in a non-VTEC head helps with low end torque though (because of higher port velocity), but then you run out of flow at higher flow and RPM. This is why an LS-VTEC setup is a nice comprimise. You have the torque from the longer LS stroke, and higher flowing ports (and better cam profiles) from a VTEC head.
There's almost no torque increase from the 1.8 mm change in stroke.
And, the torque has a LOT to do with the heads. You said it, increased velocity at lower RPM's.
An exception, is the TypeR head. The ports are much straighter, a function of the head being taller, and the tops of the ports raised. This allows a much straighter path for the airflow. Much like a Hemi head, it causes the low-lift flow (What gives you torque, for those who don't know) to be improved. It also allows for very little restriction, and a much more ideal port shape, that doesn't allow the air to "slow down" as it flows through the port. Curves in a port can hurt the flow tremendously.
So....
Take it for what you will. The smaller valves, and smaller ports allow for better low lift flow on the LS head. You swap to a LS/VTEC setup, and the only thing you really gain is some $$ saved by not having to buy a GSR or TypeR bottom end, and a very small amount of displacement. For a Turbo setup, you also end up with less compression than a straight VTEC motor, which can prove benificial. For N/A, there's no need to build a LS/VTEC. B20/VTEC, maybe....