what size Power Valve for Holley carb

[Charger72SE]

I''d like to know what size Power Valve to get when the carb gets rebuilt.  I have a 72 SE with a stock Holley 4160 on a 440 HP & automatic trans.  When the engine was rebuilt, the cylinders got a .30 over and 6 pack pistons were added - the compression went from 8.2 stock to 9.4:1

Here are the vaccum ratings under various driving conditions
fast idle 19# @ 1500 rpm   
curb idle 17# @ 1000 rpm
curb idle in Drive 15# @ 1000 rpm
35 mph 17#
40 mph 18#
50 mph 20#
60 mph 18#
65 mph 18-20#   


thanks very much!

[R2]

They usually quote about 2 inches of mercury below the lowest manifold vacuum reading you get on cruise and idle ( in gear for automatics).  

I think the biggest PV holley has is a 10.5 ( might be what you need )

Is 15# the "lowest" reading you get ? ( idle speed seems a bit high,,((1000rpm in gear ? ),,,can you turn that down a bit,,,,,your vacuum reading might drop a bit as well )

Is your timing all correct ? ( ie,,,distributor adjusted,,correct springs,,,curve,,,etc,,,before you start on the carb ),,,i had to "keep" my idle speed way up to keep the car running,,,come to find out,,,i had some bad springs in the dist,,and the dist was way off,,, i went from a idle speed of 1400 in gear to 850-900 (after i fixed and re-curved the dist ),,,,,then my vacuum reading came WAY down ),,,,,after i got this all sorted out,,,i chased the carb,,,and found i had the wrong PV's.....( had to go down 2 sizes )

Wayne Smothers DVD is helpful for this stuff,,, ( see post on Super Tuning by Big Squeeze ),,,,he emphasizes getting the timing and dist dialed in first,,,,,then chasing carb tuning.... (hopefully he will chime in)

[BBKNARF]

I think a 8.5 or maybe 6.5 may work better its something you have to play around with 
Also check out on Youtube type in Holley Carburetor Power Valve.

[R2]

BBK,
that was interesting,,,,i checked the you tube vid you mention....thanks ,,, 
This gets more confusing.....
I have several books,,,references,,etc,,and even the DVD from Big Squeeze,,,that goes over PV selection.....
All of them say to use a PV 2 sizes down from the lowest vacuum reading you get.....

The Holley you tube vid,,,,mentions dividing the vacuum reading in half,,,,and using that number for your PV,,,,

Not sure what method most people use ??

I have always used the first method....

What is everyone else doing ?

[Charger72SE]

thanks guys,

I heard 2# below vacuum at idle in drive, for an auto tranny, and that sounds real high (13#)

[greenpigs]

What is a two stage Power valve? I see on summits they list a 12.5 and 5.5 rated one.http://www.summitracing.com/parts/HLY-125-206/

I am guessing it gradually opens at 12.5 and then @ 5.5 opens completely. At $30 I would like to know & the Holley web site didn't say. I'll check Wayne's DVD to see if he covers this also.

Well Wayne didn't cover two stage power valves because from what I found they are more for fuel economy and not a performance thing. You can pick your power valve at idle in gear but you need to make sure you have your intial & total timing correct first. I am going to order a high flow 10.5 as I have similar readings as you and thats the highest they have.

[R2]

thanks guys,

I heard 2# below vacuum at idle in drive, for an auto tranny, and that sounds real high (13#)

Your idle in drive still sounds high to me....1000rpm ?

I would work on this before changing the PV's

I would expect your vacuum reading to come down some more,,,as your idle speed drops,,,, have you looked at your distributor curve,,,and timing,,,this should be dialed in FIRST,,,before tearing into the carb.........

Maybe Wayne can chime in..........

[Charger72SE]

yep, that was great suggestions, to take a look at the timing first.

As soon as the weather warms up in Wisconsin - April!!!

[FLG]

Id have the idle speed in gear at around 850~900. I remember Ron telling me the cams are splash lubed so it gets less oil at low idle, so dont turn it down too much.

[firefighter3931]

Id have the idle speed in gear at around 850~900. I remember Ron telling me the cams are splash lubed so it gets less oil at low idle, so dont turn it down too much.

Yep, set the idle speed to 850-900 and keep the cam/lifters happy. See what you've got for vacuum and size the PV accordingly. What cam are you running ? Where is your initial timing set ?


Ron

[davidn3]

First think about how the carb is working, and what the power valve does.  You have pretty high vac, which gives you choices depending on what you want.  Your jets are for cruising, and the power valve is for accelerating.  If you want a general guess to start, warm up the car, put it in gear and put the e-brake on and see what the vac is.  You should be 1.5 to 2 inch below that.  (in gear and not moving).  This will prevent the PV from opening too early and flooding the car and you will kill the engine.  If your car dies when you put it in gear that might be whats happening.  When you step on the gas peddle, your butterfly valves start to open, making the vac go down.  Then the PV will open at the point you choose. (PV that you choose).  If your PV is too low, you will get kind of a delay time, then when it opens you get a rush of fuel and power.  If it is too High of a PV it will open when you put it in gear and flood the car/loose all your vac and kill the engine.   You might have to play around with a few PVs and see how each one feels and choose the best one you like.  1000 rpm is pretty fast for curb idle in drive.  You could slow it down a bit if you want. Make sure your timing is correct, then set the idle to something around 800.  But it is all personal preference and feel.  I'd start with the 10.5" PV and see how that feels.  The 2 stage PVs have 2 settings.  I've never used one.  I think they are more for helping out with fuel millage.  It will open half way  at 10.5" and the rest of the way at 5" for a 2 stage with those settings.  Then if you accelerate normal you aren't wasting fuel, but if you stomp on it, the PV will fully open.