Originally Posted by DEpointfive0

The runners on the 370Z manifold have longer runners which is where the air is shoveled into the engine. Longer runners=higher peak HP, and in the car game, peak HP is the name of the game, no matter how unusable it may be.
So the 350Z HR's manifold has shorter runners losing peak HP by 2-4HP, BUT the total area under the curve is increased dramatically.

I personally make a 350Z HR manifold conversion and what is being done is redrilling 4 holes to make it align to the 370Z, THEN adding a top plate to add pressure because you cannot bolt up the modified manifold... (Sounds a bit easier that it really is)

Cutting a 370Z manifold with a hot knife then going about modifying would take so much R&D work and time and effort, you might as well mold a new one of out plastic, lol