The stock heat riser is an impressive piece of engineering and I sacrificed an intake to see exactly how it works. In heat on (cold engine) mode the exhaust is deflected up into the intake where it must pass over the top of the horizontal runners and then down the outbound side. Exhaust heat comes very close to the area all around the base of the carb. This leads me to believe that a Corvette exhaust manifold or split stock one are best on vehicles where immediate driveablilty is desired.
http://good-times.webshots.com/photo/2743005060023244788OCMEnj
