We seem to have similar discussions, re; “carburetor size” on a fairly regular basis on this site. I certainly can associate with a lot of the questions as this issue is only next to “cam selection” in complexity. There is a tendency to “over carburetor” because most people think bigger is better. Well, size does matter, but in the case of carburetors, if they are sized too big, you’re pouring gas “through” your engine rather than optimizing the combustion characteristics of atomized fuel at a point where the most energy may be realized. To get real “serious” about carburetor sizing, it is important to have at least a basic understanding of “volumetric efficiency”.

If you want a real detailed explanation (college level) look at: Volumetric Efficiency:* Calculating your cars volumetric efficiency

If not, here’s my simplistic (layman’s) explanation that may be beneficial: Volumetric efficiency (VE) is a measurement of how well an engine can move atomized fuel into and spent gases out of the cylinders. VE is a ratio (measured as a percentage) of what quantity of fuel and air actually enters the cylinder during induction to the actual capacity of the cylinder under static conditions. If an engine creates higher induction manifold pressures (above ambient air conditions) it is possible efficiencies greater than 100% - however it is unlikely in normally aspirated engines. Engines with higher VE will generally be able to run at higher RPMs and produce greater output.

Stock (carbureted) engines typically have VE of .75 - .85 (our German and Japanese friends have several engines in the .9 and above - but they are turbo’ed, i.e., forced induction)

A good build may get a normally aspirated engine in the .85 - .90

Full tilt boogie build (like Pat and Jerry build) will be in the .90 plus range

It sounds like you’ve got a pretty healthy build on your 383. Without knowing the specifics I’d not try and second guess your builder so I’ll make some assumptions and offer my opinion.

A 383 of your build is probably in the .85 -.9 range. At .85 with a maximum RPM of 7,000 – you’d be well served with 650CFM. At .9 we would push 700CFM at 7,000.

All that to say – I think your 800CFM (1412/1413) Edelbrock is a bit much and you’re probably not reaping any benefits over a 650CFM.

I like Edelbrocks but have found they tend to run rich out of the box and more often than not, I’ve re-jetted and installed new metering rods to prevent them from single handedly supporting OPEC. Your builder may have addressed this condition and if you’re happy with the performance, well just driver ‘er hard and enjoy!

Regards,
Glenn