Power Valve

[disco_charger]

Hey kids,
Got me a little 4-71 on top of my BBC. Going to put my HP 950 on top of it, and thinking about Power Valve size. I'm not making a ton of boost, (still running on pump [92] gas) so what kind of Power Valve set up should I be running?
Thanks
Disco

[Blown 472]

Plug it and jet up. More trouble then what it is worth. Or put a vacuum gauge on it and see if you can find one to work or spend a bunch of money to boost ref.

[Hotcrusader76]

disco_charger:
Hey kids,
Got me a little 4-71 on top of my BBC. Going to put my HP 950 on top of it, and thinking about Power Valve size. I'm not making a ton of boost, (still running on pump [92] gas) so what kind of Power Valve set up should I be running?
Thanks
Disco How do you plan to run this boat?
Cruising around, midrange power- install a boost referenced powervalve or run a 10.5in/hg valve (non-referenced)
All out W.O.T- block it! In order to jet up you need to figure out what size PVCRs you have. Then add the area of the hole IE 0.070"PVCR to the area of your current baseline main-jetting. The loss of the (Example)powervalves two #0.070"PVCR holes needs to be made up with additional jetting. The average increase shows about 6 sizes higher with Holley jets.
The HP950 is a 750 mainbody with an 850 base, stock 750 metering block PVCRs should be around 0.069-0.072" as long as no one hogged them out. The HP metering blocks show a slight increase when delivered in stock calibration of about 0.073".
I probably broke it down a little too far for ya, but it might save your spark plugs some trouble of properly calculated.
Has anyone you know prepped this carburetor for blower use? If so then I would suspect that the PVCRs were enlarged. Dual carb applications normally are around 0.070" when referenced for primary enrichment.
Good luck.
~Ty

[Hotcrusader76]

I almost forgot.
My "PV" assistant lurks around here once in awhile aka"058". He might want to add something to this cloudy issue of flappers and valves... :D

[gnarley]

[QUOTE]Originally posted by Hotcrusader76:
In order to jet up you need to figure out what size PVCRs you have.
Sorry Ty, you don't need to!
You can just block it off & go up 8-10-12 jet sizes & do a plug check after a WOT test, then adjust the jets accordingly. Holley does say about 6 sizes if I remember correctly. For many years lots of weekend warriors who didn't know what a PVCR was looked at their plugs to see if the color was right. And even if you know your PVCR sizes you still need to know what your plugs look like, so knowing it for most of us is pretty useless.

[78Eliminator]

gnarley:
You can just block it off & go up 8-10-12 jet sizes & do a plug check after a WOT test, then adjust the jets accordingly. Holley does say about 6 sizes if I remember correctly.Yeah, I am trying to stay out of carb related shit, but I read the same thing from a book published by Holley (one would think that they know a thing or two).

[Hotcrusader76]

Well, in that situation then yes! You're right, but my answers or advice isn't a 'shoot' from the hip solution.
The jetting procedure you explained does work and is a well known method among many avid gearheads.
Now the way we perform proper sizing of the jets for a blocked of PV on a particular metering block is to find the area of your 'current' jet settings and 'PVCR'orifice, add them together and that's what you will need for primary jetting. It's an accurate method within one MAX Jet size ( Comp Cams Jets (http://www.compcams.com/catalog/356.html) )
Of course everyone here understands proper plugs checks are crucial troubleshooting or checking your work. That's a no brainer.
I try to limit the 'shoot from the hip' answers so that everyone here gets the main idea of what's 'actually' going on and not just the same old "Jet up 6-10-12 sizes etc etc" answer. What does that teach anyone? Hopefully everyone got something out of my posting.
Thanks again.
~Ty

[gnarley]

[QUOTE]Originally posted by Hotcrusader76:
I try to limit the 'shoot from the hip' answers so that everyone here gets the main idea of what's 'actually' going on and not just the same old "Jet up 6-10-12 sizes etc etc" answer.
What does that teach anyone?
~Ty
It teaches self-reliance, sure anyone can send a carb out for service & it might be close or right on the money but is the carb builder going to go do the plug check also? I doubt it. If we ALL understand what happens & do our diligence in research (much Holley tech info openly available) we can do a lot of our own work ourselves & have a very good technical understanding of what is going on in the fuel circuit & then adjust it as needed or ask for help here. People don't learn from just sending out their parts for service, more often they learn from doing it & understanding the cause & affect.
Ty, to take it even a bit further I know you are or were in school & would hope learning. What have you learned & would you learn anything if you bought the answers instead of doing the research yourself?
[ April 04, 2003, 03:23 PM: Message edited by: gnarley ]

[058]

Hotcrusader76:
I almost forgot.
My "PV" assistant lurks around here once in awhile aka"058". He might want to add something to this cloudy issue of flappers and valves... :D Ty, you got it about covered. Not much I can add to your post[s] :D :D

[paradigm shift]

Well I don't have the expertise that some others here have but I vote for referencing PV on primary side. I think they run cleaner at low or part throttle. Just my .02 You have gotten some good advice from Ty.

[eliminator777]

Plug it ,Go up a min of 6