Power Valve ?
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Power Valve ?

  1. #1
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    Default Power Valve ?

    Is it necessary to boost reference the carbs,(1050 Dominators) when using power valves ? Also what # power valves should one use?

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    "It's HONDO, honey" Kyle's Avatar
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    yes to the boost reference. Generally in the smaller carbs power valves are something that you want to stay away from but if dominators are being used they are a little better. Couldn't help you on what number unfortuanatly just remember you get one backfire that is just a little bit stount and that powervalve will give and overflow like an improperly adjusted seat.
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    I thought all Holley carbs had back fire protection since the last 5 or 6 years. Or does a blower back fire have that much more force than a NA engine?

    Tim

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    Holleys come with 6.5's in them. Remember the smaller the number the easier it gets sucked shut, and turns the added fuel off. You need a vacuum gauge and take readings from the plenum under the carb plate. What's important here is that the engine has enough vacuum to pull that powervalve shut at idle. Otherwise it's going to make your mixtue way rich. You only want the power valve opening when the engine is under load and it needs the extra gas.So throttle blades open letting more air in thus dropping the vacuum and then the power valves spring opens them delivering the extra fuel needed.

    Now lets say youv'e got one bad boy blower and spining the crap out of it.
    There is a possibility that the blower will create enough vacuum at wot to suck the power valves closed. Once again a vacuum gauge can shed a little lite on this situation. It is vary bad to suck a power valve shut a wot it will lean out your mixture! But you would realy have to be spinning that blower to develope 6.5 hg of vacuum with all eight throttle bores open. Most applications do not need to be boost referenced.

    You need a vacuum gauge and A/F meter to really tune it in. Different PV's come in at different vacuum levels so you can eliminate flat spots with them. just watch the vacuum gauge and see when the engine wants more fuel and put in the power valve that opens at that vacuum level.

    Hope this helps. -Matt

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    Quote Originally Posted by VD Cruiser View Post
    Is it necessary to boost reference the carbs,(1050 Dominators) when using power valves ? Also what # power valves should one use?
    I would first want to know how much vacuum I have at the carb bases @ WOT. If you have 6.5's in the carbs and are actually pulling only 3 inches of vacuum @ WOT, they are open! If you have no 'part throttle problems', and they are open, why change? If you in fact are running the motor @ WOT and the carb base vacuum readings are high enough to close the PV's you may be able to "index the PV's" and gain horsepower. Start with the carb base vacuum readings @ WOT. "see your future, be your future"

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    Half a bubble off jrork's Avatar
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    Quote Originally Posted by GFINISHLINE View Post
    If you in fact are running the motor @ WOT and the carb base vacuum readings are high enough to close the PV's you may be able to "index the PV's" and gain horsepower.
    Okay George, gonna do it to you again by flying the newbie flag.....what the $&%@ do you mean by "index the PV's". I've never heard that one (come on, you know my elevator don't go all the way to the top)....

    Happy New Year to ya.......ya grumpy old fart.. John

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    Highaboosta Unchained's Avatar
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    From the guys who recommend boost referencing, I have yet to hear of anyone pulling a readable vaccuum at the carb base at WOT.

    Twin Turbo 1800 HP V-Drive lake boat

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    Quote Originally Posted by Trigger View Post
    No one cares about your buddies old antiquated garden hose technology.
    Quote Originally Posted by MAXIMUS View Post
    I think I could run more boost but it's a real hand full right now

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    Default What The F........?

    John, you know what I'm talking about. Installing remote vacuum hoses to the PV cavity, in an attempt to externally control the PV enrichment action. I don't disturbe the 'ported vacuum tube', I go thru the carb base plate. Then run that small vacuum line down to the "load side" of a turbo or blower intake system. On a system with a carb on top then the turbo/blower (draw thru system) and then the motor, the carb 'sees' only it's own base vacuum signal. When the motor is in boost the carb base 'sees' higher vacuum readings and would (on stock carbs) close the PVs and lean out the mixture. Indexing the PVs with a small vacuum hose to the "load side", means I will be taking my PV control signals from the area between the intake valve and the rotors/fan of the blower unit. This is where the actual "load on the motor" is more accurately seen. On a 'mild system' I try to work with the spark timing and enrichment for a smoother power flow both "on opening and closing" of the throttle plates. My old turbo dually runs 41 degrees off boost, at 4" of vacuum the vacuum advance drops out to a mechanical total of 32 degrees. The 2.5 PV opens just as the vacuum starts to drop and the secondaries start to open. At 1.5 lbs my water injection kicks in and at 5 or 8 lbs (adjustable) my waste gate starts to work. Decel is even better because it all 'leans and cleans' itself as I slow down. As the throttle closes and the boost drops/vacuum rises, the fuel leans out (PV closed at 2.5) and then the spark timing comes back to full unloaded advance 41 degrees. This makes it very clean and drivable, VS locked timing. I've done quite a few boats with this same plan and had great results. I like boost indexed carbs.

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    Come on now. Those single carb Race Aero, Banks and PFM deals with a good tune up and good spark advance curve will pull 6 inches at the base of an 850 with only 9-10 lbs of boost. I've measured them, that's how I sized the carbs. (or number of carbs to be used) PS 6 inches is 3 X the factory measurement base line and the fuel passages can't keep up with the air flow there. Edit; that's with the OLD Rayjays and RM stuff, that you had to 'force up to speeds'. Todays 'low drag' ball bearing, triple throw down stuff makes everything easyer to overpower.
    Last edited by GFINISHLINE; 01-25-2009 at 04:13 PM.

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    Highaboosta Unchained's Avatar
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    I agree on the single carb and turbo application George.

    His question I believe is based on two carbs on a roots blower.

    Twin Turbo 1800 HP V-Drive lake boat

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    Quote Originally Posted by Trigger View Post
    No one cares about your buddies old antiquated garden hose technology.
    Quote Originally Posted by MAXIMUS View Post
    I think I could run more boost but it's a real hand full right now

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    If two of any carbs or injector hat had NO VACUUM at the blower top, what makes the fuel go into the motor? Gravity? There is always vacuum, low pressure or velocity, but it's still vacuum in a supercharged motor. (when running) If there were no vacuum at the intake of any motor (as we know motors) there would be no INTAKE. If the roots blower motor (as described) had NO VACUUM at the blower intake at WOT. This would show that the outside pressures (baro) and the inside pressures (???) are equal, correct? This would show that the air flow would stop! You can install BIG CARBS on a slow blower, and have a difficult time measuring 'base vacuum' but that does not show the fact that 'pressure differnences don't exist' and there is velocity vacuum between the outside and the carb base. (high RPM motors) If this were not present, the motor would backfire and stall! Then, if the blower has no 'inlet vacuum' then it must not be DRAWING IN ANY AIR! So it stopped too? "Let's not try to fool (each other and) mother nature!"

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    Quote Originally Posted by Unchained View Post
    I agree on the single carb and turbo application George.

    His question I believe is based on two carbs on a roots blower.
    This is true. I asked this question because I am helping a friend and he wants to use the power valves and I was a little concerned that at wot they might get pulled shut. On my deal I don't use the power valves and I don't have any problems at idle, part throttle or wot. I thought I might just try the power valves on his without referencing them. Sounds like I need to use a vacuum gage to determine what #'s to start with.

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    Once you know where you are at, you will know which direction to go.

  16. #14
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    Quote Originally Posted by GFINISHLINE View Post
    Once you know where you are at, you will know which direction to go.
    Thanks George, I think I know what you mean.

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