Holley 600 Dual-stage PV

[R. Shackleford]

Hello all. I have a Holley 80454 600cfm that I bought from AllState Carbs (I know, should have checked here first but what ya gonna do). It's the factory upgrade for '65-'67 Mopars so I've read. This model has a dual-stage power valve (10.5-5.5). Apparently they are made of unattianuim and was wondering if anyone has swapped a dual-stage for a single? If yes then should I land somewhere in the middle like maybe an 7.5 or 8? Thanks for the read

 

[ckessel]

Haven't seen any mention of one of those for many years. General rule of thumb was to choose a valve that opened 1- 1.5" vacuum under what it idles at in gear, if auto. Most of their carbs just came with a 6.5 unit.

 

[R. Shackleford]

Yeah I saw the standard was 6.5 for Holleys but wanted to make sure cause I haven't found anything on goin from 2 stage to single and if there are any benefits to it. Carb runs pretty good except for a little flat spot off idle and the idle mixture screws are funky... The engine idles better and the manifold vacuum goes up as they tighten. I can run it with them all the way in even and its smooth so somethins up with the internals. I was running a 3/8 fuel line so went to 5/16 and that settled things a little. Floats are set perfect but unsure of what jets are in it or how good the passages are. Any ideas?
On a 318 poly with mild cam
14 BTDC
Automatic
Mechanical fuel pump (factory spec)

 

[R. Shackleford]

Ok UPDATE. Just heard back from AllState about the carb (3rd attempt) and they say it is a reverse idle carb where the idle mixture screws fattin as they tighten instead of leaning out. Didn't realize that so great information to have.

 

[ckessel]

Ok, I was thinking it was one of the Economaster versions with that 2 stage valve. Your main jets may have 3 instead of 2 digits on them. If so, those are close limit jets. They too can swap with normal. And yes the mixture screws are opposite normal on adjustments.

 

[steve340]

Those two stage power valves were typically fitted to carbs with an economy and emissions in mind.
They were in some performance carbs evidently. But these carbs would have had a special calibration of metering blocks and probably very small jets.
Holley state do not use these valves in a vehicle used on a drag strip.
The book states that your power valve is for high altitude.
If you swap to a single stage the engine might go very lean before the PV opens.
You need to be cautious playing around with that carb.