Holley question, what do think of Vacuum Secondary vs "Double Pumper"?
A properly tuned double pumper will MOP THE FLOOR with any comparable vacuum secondary. However, balls out performance is not what everybody is always after.
A vacuum secondary with an automatic on the street is usually a better match because they have a much smoother transition to the secondary circuit. Tuned properly, you can barely feel the secondary circuit come in, but simply feel smooth acceleration.
Conversely, you will feel a double pumper's transition into the secondary circuit. It is a "harder" hit if you will due to the extra shot of fuel. This is why for performance, the double pumper is considered superior.
However, the double pumper will in all likelihood get worse fuel mileage in the same situation. Sometimes by a good little bit. I've always looked at that by saying the engine "probably needed it".
I looked at the decision the same Larry Shepard talks about it in the Mopar Engine Manual.....which you should already have, btw. With a mild street build with an automatic, mild converter and street gears, the vacuum secondary is a better choice, for the reasons I outlined above.
With a more hot build with a higher flash converter, or a manual transmission, lower gear ratios (numerically higher) the double pumper will have better performance.
The double pumper properly tuned will have better performance in either situation simply because it is a higher performance carburetor. It simply boils down to what you WANT.
