How cold is it there where you are in NC? I ask because my 383 came with that GM performance manifold (12496820). I live in Montana where it can get very cold in winter and even in the summer can get cold at night.
I spent a year fighting with 2 carbs and then fuel injection trying to figure out why when it was less than 45 degrees it would run like crap.
It was the intake manifold. Vortec heads do not have the exhaust crossover that puts exhaust under the carb in the intake manifold. Plus the design of that manifold is perfectly smooth under the carb. Most manifolds have a waffle pattern or "speed bumps" on the manifold there. When atomized fuel hits cold metal and has to change direction by 90 degrees the fuel can drop out of suspension. This makes a puddle of fuel form. By having raised ridges then the fuel can lift off and be carried away by the air.
After finally figuring that out I bought an Edelbrock 7116 manifold that you can plumb either exhaust or coolant thru a heat passage under the carb.
Unfortunately I bought a defective one. Somehow after driving it and the engine would cool down it would leak coolant up into the intake plenum and would then burn off a very small bit of coolant next time I would start it up. Edelbrock said they had never heard of that before. I bypassed the heat plenum and the coolant loss problem went away. So- I bought a second @#$^$# Edelbrock 7116 and installed it. All is good now. The manifold heats up pretty fast with having coolant go thru it.
And speaking of coolant... when using Vortec heads there is supposed to be a coolant bypass:
Any small block engine, regardless of year, that uses Vortec heads, will require an external coolant bypass line from the intake
manifold to the 5/8" hose nipple on the water pump (passenger’s side). Suggested routing is from the 3/8 NPSF boss on
intake manifold to the water pump.
With the 7116 manifold I'm running the bypass from the front fitting near the thermostat to the heat plenum under the carb then to the return on the water pump. This allows circulation before the thermostat opens.
I also have a loop from the intake manifold thru the heater core back to the top of the radiator. At first I tried just the heater loop- but had wild coolant temperature fluctuations. The other loop stopped all of this.
cannot remember sorry. They were about $200 on Jegs but were on sale. Flowtech is the other brand Holley makes and they might be cheaper. I also used Hookers 2 1/4 exhaust pipe kit to complete the exhaust.
