A heat riser has a spring, a flap valve, and a counterweight to route exhaust gas under the carburetor during engine warmup. On a V8, there are passageways through both cylinder heads and the intake manifold to facilitate the gas flow to the carburetor until the bimetal spring relaxes and the gas flow and the counterweight pushes the valve open. That open hole has none of those things, and is used by people who don't think the engine designers who went to a great deal of effort to build the system knew what they were doing. The standard excuse that "I'm in a warm climate" doesn't take into account that exhaust gas is somewhere in the 1,000 degree F. range or more.
This is the correct heat riser for a 2" pipe manifold- - - -ignore the "Corvette" designation. There are others on Ebay for lots more money that just say "2 inch".
https://www.ebay.com/itm/224312028645?hash=item343a09ede5:g:aUMAAOSw7Ilf-49p
Jerry
