Selecting power valve method Holley 4160
Hey guys I been reading up on Holley seems like there’s two ways to select a power valve, which one do you guys use?
In gear warmed up I am at 15 inches of mercury and cruising light throttle I am at 22 inch or mercury
Neither one is really correct.
The second one is closer to the functional reason for enrichment.
Enrichment is needed under heavy load.
Manifold vacuum is a good indicator of load.
Do I hear you ask:
How heavy? How does that translate to manifold vacuum?
It depends on the engine. An engine that is more efficient at part-throttle, and has good part throttle fuel distribution, needs enrichment only close to full throttle. For this sort of engine, full enrichment may not be needed until 4 to 6 in-Hg. An engine that doesn't have those characteristics, or maybe is used to pull very heavy loads, will need enrichment sooner. Chevy's 1965 396 used Holley 3310 that came with 10.5 (& 8.5 secondary) PV. Chrysler Hemi with Holley had a 8.5 PV. Those should give you some idea of the ranges that a hopped up engine may want.
If you are already driving the car around, and have a vacuum gage, then see if you notice any flat spots or delays in acceleration as you increase the throttle. If its at consistant vacuum, thats a clue the PV is not enriching at the correct load. You get fancier and more scientific - all depends on how much work you want to put into it.
One other important point. More timing for lean conditions. When the engine wants enrichment, it also will then need less vacuum advance. There should be no vacuum advance at full enrichment. These two things work together.
