Welcome to Club Hot Rod!  The premier site for everything to do with Hot Rod, Customs, Low Riders, Rat Rods, and more. 

  •  » Members from all over the US and the world!
  •  » Help from all over the world for your questions
  •  » Build logs for you and all members
  •  » Blogs
  •  » Image Gallery
  •  » Many thousands of members and hundreds of thousands of posts! 

YES! I want to register an account for free right now!  p.s.: For registered members this ad will NOT show

 
Like Tree11Likes
  • 1 Post By mrmustang
  • 1 Post By rspears
  • 2 Post By jerry clayton
  • 4 Post By mrmustang
  • 3 Post By rspears

Thread: Power valve do I need one?
          
   
   

Reply To Thread
Results 1 to 13 of 13
  1. #1
    Jed Rumbolz is offline CHR Member Visit my Photo Gallery
    Join Date
    Aug 2015
    Location
    Mitchell
    Posts
    10

    Power valve do I need one?

     



    I'm running a 68 impala 4 door with a 381 sbc pump gas engine has a QF 950 runs a single power valve in the front. Almost everyone tells me to plug it, but I am skeptical because this engine sees different plenum vacuum readings when staged and at WOT going down the track. when foot braking the plenum is at 8 in and at WOT crossing the line at 6800rpm the plenum is pulling 2 to 3 in, take in to account this engine gets shifted at 7200rpm.

    So the Main system in a carb basically operates of vacuum a pressure drop in the main venturis(boosters/doglegs) pulls a mixture of air and fuel from the main system in the carb. As engine rpm increase you displace more over a giving time. More air is moved through the intake in a giving time, the flow is faster, the pressure drop gets higher over the venturis and pulls more air and fuel.

    THE POWER SYSTEM
    I am on the understanding that the power system exists in a carb because at WOT throttle when the plenum vacuum drops this can cause the pressure drop to lower over the venturis and make the the main system inefficient and not deliver enough fuel where as air has more of a tendency to just fall in the carb and cause a leaning effect and power loss. So it basically corrects Air:Fuel ratio at high engine loads

    Would it be beneficial to have in my car? I could justify not having one if this was a car that only saw 6000rpm and up all the way down the track, but the engine in my car operates between 3000rpm to 7200rpm the duration of the run
    Last edited by Jed Rumbolz; 08-29-2015 at 10:15 PM.

  2. #2
    mrmustang's Avatar
    mrmustang is offline Global Moderator Lifetime Contributor Visit my Photo Gallery
    Join Date
    Apr 2001
    Location
    Greenville
    Car Year, Make, Model: 1969 GT500 Fastback
    Posts
    1,349

    What are the specs of your engine

    Compression ratio
    Heads (type, intake/exhaust sizes)
    Cam specs
    Intake
    Ignition

    Has the car been on a CHASSIS (not engine) dyno?

    Once we have these items, we can then decide whether you need a new power valve, or perhaps a small carb.

    Bill S.


    Quote Originally Posted by Jed Rumbolz View Post
    I'm running a 68 impala 4 door with a 381 sbc pump gas engine has a QF 950 runs a single power valve in the front. Almost everyone tells me to plug it, but I am skeptical because this engine sees different plenum vacuum readings when staged and at WOT going down the track. when foot braking the plenum is at 8 in and at WOT crossing the line at 6800rpm the plenum is pulling 2 to 3 in, take in to account this engine gets shifted at 7200rpm.

    So the Main system in a carb basically operates of vacuum a pressure drop in the main venturis(boosters/doglegs) pulls a mixture of air and fuel from the main system in the carb. As engine rpm increase you displace more over a giving time. More air is moved through the intake in a giving time, the flow is faster, the pressure drop gets higher over the venturis and pulls more air and fuel.

    THE POWER SYSTEM
    I am on the understanding that the power system exists in a carb because at WOT throttle when the plenum vacuum drops this can cause the pressure drop to lower over the venturis and make the the main system inefficient and not deliver enough fuel where as air has more of a tendency to just fall in the carb and cause a leaning effect and power loss. So it basically corrects Air:Fuel ratio at high engine loads

    Would it be beneficial to have in my car? I could justify not having one if this was a car that only saw 6000rpm and up all the way down the track, but the engine in my car operates between 3000rpm to 7200rpm the duration of the run
    36 sedan likes this.

  3. #3
    rspears's Avatar
    rspears is offline CHR Member/Contributor Visit my Photo Gallery
    Join Date
    Sep 2007
    Location
    Gardner, KS
    Car Year, Make, Model: '33 HiBoy Coupe
    Posts
    9,542

    Is this a track only car, or do you depend on it for street operation and want it to have good street manners, too?
    36 sedan likes this.
    Roger
    Enjoy the little things in life, and you may look back one day and realize that they were really the BIG things.

  4. #4
    jerry clayton's Avatar
    jerry clayton is offline CHR Member Visit my Photo Gallery
    Join Date
    Feb 2006
    Location
    Bartlett
    Posts
    6,748

    The use of a power valve lets a carb (Holley in this case) be set up to run leaner during normal everyday to the market/school drives for more effiency but will richen up the mixture equal to 5 -6 jet sizes at a low vacume which occurs at higher throttle positions-

    These days-------fuel sucks, no such thing as vacume(well if there was a perfect vacume there wouldn't be anything so evedently there isn't any such thing as vacume)

    How much etonal does your fuel have in it? If you are racing why not use 100+ race fuel? For racing you could lock the advance in dist and only retard it for starting--

    Have you verified tdc and all the markings on your crank pulley???
    NTFDAY and 36 sedan like this.

  5. #5
    rspears's Avatar
    rspears is offline CHR Member/Contributor Visit my Photo Gallery
    Join Date
    Sep 2007
    Location
    Gardner, KS
    Car Year, Make, Model: '33 HiBoy Coupe
    Posts
    9,542

    ..................
    Last edited by rspears; 08-30-2015 at 12:04 PM.
    Roger
    Enjoy the little things in life, and you may look back one day and realize that they were really the BIG things.

  6. #6
    Jed Rumbolz is offline CHR Member Visit my Photo Gallery
    Join Date
    Aug 2015
    Location
    Mitchell
    Posts
    10

    Quote Originally Posted by mrmustang View Post
    What are the specs of your engine

    Compression ratio
    Heads (type, intake/exhaust sizes)
    Cam specs
    Intake
    Ignition

    Has the car been on a CHASSIS (not engine) dyno?

    Once we have these items, we can then decide whether you need a new power valve, or perhaps a small carb.

    Bill S.
    Billy

    We run a 11.5:1 static compression ratio with 91 octane pump gas
    heads are iron 190cc darts ported to about 200c, they run a 2.05'' intake and a 1.68'' exhaust
    cam specs- solid roller, both intake and exhaust lifts are in the .660'' lift range and the duration for both are around 260 degrees @.50'', 109 LSA, and the Intake centerline I think is 108 degrees
    Intake manifold is a 5.8'' tall holley strip dominator single plane
    Carb is a 950 QF with a 1'' spacer underneath
    headers have 1-5/8'' primaries with a 3'' secondaries
    ignition- MSD 6Al-1 box, MSD distributor, coil is a master blaster

  7. #7
    Jed Rumbolz is offline CHR Member Visit my Photo Gallery
    Join Date
    Aug 2015
    Location
    Mitchell
    Posts
    10

    Bill the car has not seen a dyno of any kind. I agree, I think it needs a larger carb, this is a father son drag team and pops doesn't want to try a 1050 at the time

  8. #8
    Jed Rumbolz is offline CHR Member Visit my Photo Gallery
    Join Date
    Aug 2015
    Location
    Mitchell
    Posts
    10

    Quote Originally Posted by rspears View Post
    Is this a track only car, or do you depend on it for street operation and want it to have good street manners, too?
    It did see quite a bit of street use but now only on once in a while

  9. #9
    Jed Rumbolz is offline CHR Member Visit my Photo Gallery
    Join Date
    Aug 2015
    Location
    Mitchell
    Posts
    10

    Quote Originally Posted by jerry clayton View Post
    The use of a power valve lets a carb (Holley in this case) be set up to run leaner during normal everyday to the market/school drives for more effiency but will richen up the mixture equal to 5 -6 jet sizes at a low vacume which occurs at higher throttle positions-

    These days-------fuel sucks, no such thing as vacume(well if there was a perfect vacume there wouldn't be anything so evedently there isn't any such thing as vacume)

    How much etonal does your fuel have in it? If you are racing why not use 100+ race fuel? For racing you could lock the advance in dist and only retard it for starting--

    Have you verified tdc and all the markings on your crank pulley???
    Jerry TDC has been verified,
    I have heard locking the advance WOT makes for a poor running engine at idle and makes unnecessary heat, I cant run through the pits like a nascar after all you gotta drive like granny going to church
    $3.00 a gallon is nice price for fuel going down the track, I wouldn't consider using race fuel unless we jacked the compression ratio.

  10. #10
    jerry clayton's Avatar
    jerry clayton is offline CHR Member Visit my Photo Gallery
    Join Date
    Feb 2006
    Location
    Bartlett
    Posts
    6,748

    but----------you have jacked the compression ratio and with iron heads-------

  11. #11
    mrmustang's Avatar
    mrmustang is offline Global Moderator Lifetime Contributor Visit my Photo Gallery
    Join Date
    Apr 2001
    Location
    Greenville
    Car Year, Make, Model: 1969 GT500 Fastback
    Posts
    1,349

    With your engines specs, you actually need a smaller carb (850cfm properly tuned), not a larger one. If strictly a drag car, then a QF-R 850cfm carb , if a street car, then a 850cfm street carb . You;ll find that when it comes to carburetion , bigger is not always better, a few hours on a chassis dyno with someone that knows how to tune the carb, will be the proof needed.


    Bill S.

  12. #12
    36 sedan's Avatar
    36 sedan is online now CHR Member Visit my Photo Gallery
    Join Date
    Apr 2012
    Location
    american canyon
    Car Year, Make, Model: 36 Ford Sedan, 23 T Bucket
    Posts
    1,403

    Like Bill says, and the dyno will also solve your ignition/timing curve questions.

  13. #13
    rspears's Avatar
    rspears is offline CHR Member/Contributor Visit my Photo Gallery
    Join Date
    Sep 2007
    Location
    Gardner, KS
    Car Year, Make, Model: '33 HiBoy Coupe
    Posts
    9,542

    And you'll need the power valve to drive like granny going to church in the pits, without fouling your plugs.
    Roger
    Enjoy the little things in life, and you may look back one day and realize that they were really the BIG things.

Reply To Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
Links monetized by VigLink