Home | Register | Login | Contact Us

 
Auto Math
Classifieds
Forum
Gallery
Games
Garage
Tech Articles
Utilites
 
FAQFAQ    SearchSearch    RegisterRegister    Log inLog in    Log in to check your private messagesLog in to check your private messages    Forum Subscriptions1/4 Mile Table 

Power valve in a holley Double pumper 750
Goto page 1, 2  Next
 
Post new topic   Reply to topic    SMOKEmUP.com Forum Index -> Chevy - Big Block
View previous topic :: View next topic  
Author Message
seventy468
Member


Joined: 13 Oct 2008
Posts: 92
Location: Indiana
2674.60 points



PostPosted: Thu Aug 20, 2009 7:53 pm    Post subject: Power valve in a holley Double pumper 750 Reply with quote

Someone please explain what a power valve is/does. Keep in mind I am still learning, so be nice! I also see holley offers a power valve block off to get rid of the power valve, for racers? This car is a street strip car.
Back to top
View user's profile Send private message
af2
Member


Joined: 01 Sep 2003
Posts: 5403
Location: grassvalley, ca
66636.48 points


1933 Willys Coupe

PostPosted: Thu Aug 20, 2009 9:08 pm    Post subject: Reply with quote

Keep it and tune it to the vacuum you run off idle to half throttle. With a cam usually a 5" will do it.
Back to top
View user's profile Send private message
seventy468
Member


Joined: 13 Oct 2008
Posts: 92
Location: Indiana
2674.60 points



PostPosted: Thu Aug 20, 2009 9:22 pm    Post subject: Reply with quote

if you have a back fire threw the carb, does that usually ruin a power valve? and a bad power valve will have what symptoms?
Back to top
View user's profile Send private message
10sec.et
Member


Joined: 29 Mar 2006
Posts: 3231
Location: Houston,Texas
338808.44 points


1969 Oldsmobile Cutlass

PostPosted: Thu Aug 20, 2009 9:51 pm    Post subject: Reply with quote

it certainly can ruin the PV. there are kits to prevent damage to the PV with a little check ball and spring. i used to think those little PV saver kits were the greatest thing since sliced bread, until today. i took my 850 DP apart for some "tweaking" and noticed that both check balls were gone from the factory installed kits Shocked . the spring and washer were there but i guess my engine has ingested the little check balls Evil or Very Mad . at this point, im thinking ill just keep a couple extra power valves in my tool box. no, im not tearing into the 455 looking for them.
_________________
af2 wrote:
It seems we can look at our magical Balls and come up with a fix?

Back to top
View user's profile Send private message
MufflerBearings69
Member


Joined: 22 Jul 2007
Posts: 746

25364.28 points


1968 Ford Galaxy

PostPosted: Fri Aug 21, 2009 8:27 am    Post subject: Reply with quote

seventy468 wrote:
if you have a back fire threw the carb, does that usually ruin a power valve? and a bad power valve will have what symptoms?


Bad power valve = dumping fuel

Last time I had one go, the only way to make it home without much issue was to spend a gratuitous amount of time WFO

I can tell you, it was heartbreaking.... hahaha

But yeah, when they get ruptured fuel can just pour out, which will cause a rich condition at most anything but WOT as the PV should be open then anyways...

They sell a thing to test them but really if the carb is not brand spankin new I would put one in if its questionable. The price of the adapter to test them isnt worth it for one carb in my opinion.

Block off plug- if you go that route, keep in mind whichever side of the carb you do this to must be jetted up- the books I have read have suggested something like 8-10 jet sizes up. 99% of the people who have taught me told me to not do that, and to just run the right PV for my vacuum...

idle vacuum reading- divide by 2- round to nearest available value.

_________________
Budgets were meant to be broken.
Back to top
View user's profile Send private message
lun40119
Member


Joined: 22 Oct 2008
Posts: 624
Location: Wisconsin
4738.92 points


1967 Chevrolet Chevelle

PostPosted: Fri Aug 21, 2009 7:01 pm    Post subject: Reply with quote

OP, the power valve supplements the main circuit during tip, and during WOT, or any other time the manifold vacuum drops below the stated value of the pv. They are a great thing, they allow you to tune your part throttle AFR, with the primary jets, and not affect the wot tune. I like to cruise lean, but use the power valve channel restrictors to enrich the main circuit during wot. If you are going to try to tune with the pvcr, it is a good idea to have a wideband, either a handheld or on a chassis dyno. I like to use a chassis dyno. I hope this makes sense, it does in my head.
_________________
Jake

Drag Week 2012 1st Place SB/NA
Drag Week 2011 2nd Place SB/NA
http://www.youtube.com/watch?v=skLbhe2CBAU
Back to top
View user's profile Send private message
clay
Moderator


Joined: 24 Nov 2002
Posts: 3163
Location: South Carolina
316291.67 points


1972 Chevrolet Nova

PostPosted: Sat Aug 22, 2009 10:34 pm    Post subject: Reply with quote

Pretty much summed up operation but here's a quick way to check it before you put it on the engine. Put the carb on a stand and fill the bowls through the vent tubes. If the valve is ruptured or the gasket is leaking there will be fuel running out of the bottom coming from the vacuum port that leads to the power valve chamber. I have had two power valves really kick my butt. One had threads that weren't cut quite far enough and when the valve snugged down, it hadn't pinched the gasket. Finally found it with a feeler gauge between the gasket and valve. Another one had a nylon gasket and there were 4 indentions where I'm assuming pins had pushed it out of the mold - leaked just enough that the idle mixture screws wouldn't do anything. Clay
_________________
I have done so much with so little for so long, I can now do anything with nothing.
Back to top
View user's profile Send private message
lun40119
Member


Joined: 22 Oct 2008
Posts: 624
Location: Wisconsin
4738.92 points


1967 Chevrolet Chevelle

PostPosted: Sun Aug 23, 2009 8:23 pm    Post subject: Reply with quote

Another way to check it on the engine is to make sure it is all the way down into the idle circuit. The turn the idle mixture screws all the way in, if it doesn't quit, that means that the PV is supplementing. If it quits, you are fine.

On a lighter not, I have stopped using the checkballs in the base plate. On my last engine I had a cam in it that was pretty dirty down low. Lots of overlap, anyway long story short reversion at low gramma putt, putt rpms caused the checkball to stick in the baseplate creating a NASTY lean WOT tune. Popcorn anyone!!!!!!

_________________
Jake

Drag Week 2012 1st Place SB/NA
Drag Week 2011 2nd Place SB/NA
http://www.youtube.com/watch?v=skLbhe2CBAU
Back to top
View user's profile Send private message
10sec.et
Member


Joined: 29 Mar 2006
Posts: 3231
Location: Houston,Texas
338808.44 points


1969 Oldsmobile Cutlass

PostPosted: Mon Aug 24, 2009 12:23 am    Post subject: Reply with quote

lun40119 wrote:
On a lighter not, I have stopped using the checkballs in the base plate.


yeah, me too Laughing Laughing

_________________
af2 wrote:
It seems we can look at our magical Balls and come up with a fix?

Back to top
View user's profile Send private message
nomad239
Newbie


Joined: 01 Jul 2007
Posts: 7

291.86 points



PostPosted: Sun Dec 05, 2010 7:04 pm    Post subject: Reply with quote

TO PICK THE RIGHT PRIMARY PV TAKE A VACUUM READING AT IDLE.GET A PV THAT OPENS 2" LESS THAN THAT VACUUM READING IF YOU ARE RUNNING TWO PV'S THE SECONDERY PV SOULD BE ANOTHER 2" LESS.THIS WILL MAKE GOOD POWER AND DRIVEABILITY AS WELL AS FUEL MILEAGE.
Back to top
View user's profile Send private message
robins44
Member


Joined: 29 Dec 2007
Posts: 616

18184.50 points



PostPosted: Sun Dec 05, 2010 8:50 pm    Post subject: Reply with quote

nomad239 wrote:
TO PICK THE RIGHT PRIMARY PV TAKE A VACUUM READING AT IDLE.GET A PV THAT OPENS 2" LESS THAN THAT VACUUM READING IF YOU ARE RUNNING TWO PV'S THE SECONDERY PV SOULD BE ANOTHER 2" LESS.THIS WILL MAKE GOOD POWER AND DRIVEABILITY AS WELL AS FUEL MILEAGE.


Good to know Cool
Back to top
View user's profile Send private message
squeeezer
Member


Joined: 02 Mar 2007
Posts: 2417
Location: new richmond WI
191253.78 points


1991 Chevrolet Camaro

PostPosted: Mon Dec 06, 2010 12:45 pm    Post subject: Reply with quote

^^^^^^^^^that can be used for a generic starting point

not absolute

some people go with 1 inch lower that idle

some (and i dont get this one) go with 1/2 idle vacuum

if i do it for mileage(you got the wrong carb for that)you drive around with a vacuum gauge taped to your windshield and taylor it to your driving style

_________________
Back to top
View user's profile Send private message
MufflerBearings69
Member


Joined: 22 Jul 2007
Posts: 746

25364.28 points


1968 Ford Galaxy

PostPosted: Mon Dec 06, 2010 4:35 pm    Post subject: Reply with quote

squeeezer wrote:
^^^^^^^^^that can be used for a generic starting point

not absolute

some people go with 1 inch lower that idle

some (and i dont get this one) go with 1/2 idle vacuum

if i do it for mileage(you got the wrong carb for that)you drive around with a vacuum gauge taped to your windshield and taylor it to your driving style


What I learn is only as good as the books I read... AS I recall at least 2 books on Holleys I read suggested this calculation.

That's why I come here and ask for the help from all of you with real life experience Very Happy books establish a foundation but arent the whole story

_________________
Budgets were meant to be broken.
Back to top
View user's profile Send private message
squeeezer
Member


Joined: 02 Mar 2007
Posts: 2417
Location: new richmond WI
191253.78 points


1991 Chevrolet Camaro

PostPosted: Mon Dec 06, 2010 5:50 pm    Post subject: Reply with quote

yeah what he said^^^^^^^^^^^^^^^^
_________________
Back to top
View user's profile Send private message
MufflerBearings69
Member


Joined: 22 Jul 2007
Posts: 746

25364.28 points


1968 Ford Galaxy

PostPosted: Mon Dec 06, 2010 8:21 pm    Post subject: Reply with quote

I came back to make sure I didnt come across wrong- I wasnt upset or trying to argue- just saying, some of the books on the market have some weird crap in them... Just because its published doesnt make it golden right?
_________________
Budgets were meant to be broken.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    SMOKEmUP.com Forum Index -> Chevy - Big Block All times are GMT - 5 Hours
Goto page 1, 2  Next
Page 1 of 2

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
Home | Contact Us | Automath | Cam Files | Dyno Search | Forum | Garage | Picture Gallery | Reaction Timer

Copyright 1997-2014 SMOKEmUP.com All rights reserved.
Advertising Info     Disclaimer     Privacy Policy