Will headers make a difference on a stock 318 2bbl in place of stock exhaust manifolds with dual exhaust??? I say in the video that I used 2 1/4" pipe, but it was 2.5". Here are real world results !!!
Manifolds do not exactly aid pulse tuning/timing. Because most have a common log there is cross communication that dilutes the incoming fresh charge with hot exhaust on most cylinders.
If the header lengths are about right for the engine there is no or very little cross communication and you get a low wave coming back to the exhaust valve just before the IVO. Carb tuning is probably going to be required. 2V or 4V the intake wave tuning may be different, which needs to match the low exhaust with a high pulse just at IVO.
A 4V with its likely higher flow volumns should see greater benefit.