Retune my entire carb after installing new heads?

DrCharles said

I didn't notice any difference on the butt-dyno in low- and mid-range performance when I went from an 800 to a 950 (once I dialed it in). But a smaller carb may cost enough power that it kills some of the increase from going to good heads!

This is the first I've ever heard of "compression time"... not to say it isn't a thing, but isn't that why lower compression and less dense fuel mixtures benefit from more advanced ignition timing?

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How much you compress the mixture depends on when you close the intake valve for cylinder pressure to build and compressing the mixture helps convert it to a burnable state. The problem is you think of an engine as an air pump so fuel condition doesn't enter into your frame of reference. Yes fuel needs to be conditioned for it to be able to burn. Liquids don't burn in cylinders gasses do so what comes out of you carb is a liquid droplet that needs to be converted to a gas to actually use it. Most likely you have every little vacuum in the intake tract to do this (gasify the liquid) you need more compression time to do just that on the compression stroke. When you have none of that its one big mess and a tuning headache....

How to Pick the Best Carburetor for a Street/Strip Car

Look at the ET from the 650 DP on 425 cubes and look at the vacuum it generated @ WOT. It ran the quickest ET and highest MPH. Surely it was choking that 425 to death......