1. Originality 2. If you compare an Edelbrock manifold to a standard cast manifold side by side you will see the intake ports are smaller than the original manifold. I would say the OE manifold is 10-15% larger port size.
More airflow = more power assuming you can exhaust it fast also.
The originals are heavier by far, but the added flow should be better for my 400 than the Edelbrock, in my opinion.
Advice given to me was that the Edelbrock manifolds are fine for a 350 with standard HP.
As far as the Quadrajet - So many people have told me that they are great carbs for our birds and well capable. I picked up a 68 GTO auto carb for $5 and will have it rebuilt. If set up properly based on the engine set up, it should be better than my 600 cfm Holley. They also have very large secondaries and I know in my case will pull more air than the Holley. The Q-Jet is a 750 CFM vs. my Holley at 600 CFM.
Again this is only my opinion. My 400 with a low compression rebuild back in the 80's with maybe 275HP ran out of air at the higher RPM's. My new rebuild is bringing back the compression and needs to breathe with the cam I chose.
