The Edelbrock carburetor is super easy to modify with basic rod and jet changes. I've done it many many times because they seem to run on the lean side. The plate used on a spread bore manifold is no problem either its only an 1/8th inch thick between 2 thin gaskets and it works very well. This set up is fine unless you want originality. In my opinion though the Q jet works better and properly set up they rock. I've bought a lot of cars that had the Edelbrock carb on them. I think this is because of the issues Qjets can have but they are all fixable. It just seems easier to buy a new carburetor. Long story but if you have a good Q jet i'd use it.
Q-Jets are very precisely engineered for each respective vehicle, way beyond just the rods & jets. When using a properly rebuilt core, with correct parts (floats, cams, hangers, pull-offs), the performance and durability is top notch.
We recommend the 600cfm Edelbrock for the power pack because that package is designed for guys swapping from a 2 barrel to 4 barrel, or upgrading to a performance intake over the stock one. Those engines are usually all stock to begin with, so they don't require a lot of air flow, and the Edlebrock works really well out of the box compared to most other carbs that we have experienced. We get virtually no call backs on those carburetors from guys running them. If you were to dyno them, it might not make as much horsepower as a Holley, but it's super reliable, has great throttle response, and respectable performance and economy. The adapter plate will make negligible difference in power. The last engine we dyno'd made more power with a 5/8" square bore to spread bore adapter compared to a square bore or 4 hole spacer. The benefit of a quadrajet is the small primaries for cruising and the large secondaries when you need the power. They can be a great carburetor when setup properly, I think it comes down to personal preference and what you're comfortable with. A 780cfm Quadrajet performs very close to a 750cfm Holley and is down a few horsepower to a 850cfm Holley on 455's with our experience, so it's more cfm than anything. Those were older design Holley carbs though, so the newer stuff is probably a little better these days. 350's don't need as much air as people think they do, the 455's definitely benefit from larger carburetors because of the bigger bore to stroke ratio. I wouldn't run more than a 750-850cfm Holley on a 350 unless you really have it dialed in or are running a large cam. Dual plane intakes will like a larger carb over a single plane. Too big of a carb and the engine wont be able to draw on it hard enough for it to perform properly and you'll have weird things happen with the fuel mixture.
Thank you Mike! If I read this correctly, the Edelbrock was not set up in any special way for this purpose. I was running the Q-Jet on a stock 74 intake and a mild cam before this build. Maybe that is why I was not so impressed with the dyno sheet. At least I should have about the same as I did before. The Q-Jet is an 800 cfm from a 74 350 Century wagon. With all that said, I will run the Edelbrock for now. Later, when I get this thing on the road again.. I may swap just to see the difference. I was told to consider a larger adapter so I'll check out the 5/8". Thank you all for your input, suggestions and knowledge! I hope to set the engine in place next week.
