behind the power valve is two small passages that provide additional fuel as a power enrichment circuit...

if u floor the gas....vacuum drops to zero...power valve opens and provides additional gas...

most holleys with two metering block in them ...the primaries will be about 8 to 10 jets leaner then the secondaies.

the pvrc provides that additional fuel....so u can cruise on a leaner mixture...then get more gas went u floor it...

Tony

70 AARCuda Vitamin C
71 Dart Swinger 360 10.318 @ 128.22(10-04-14 Bakersfield)
71 Demon 360 10.666 @122.41 (01-29-17 @ Las Vegas)
71 Duster 408 (10.29 @ 127.86 3/16/19 Las Vegas)