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Boost Referencing a Carb

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    Half a bubble off jrork's Avatar
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    Default Boost Referencing a Carb

    Hi guys. Is it really this easy??? I would like to get my Holleys boost referenced as I currently am PV plugged and jetted up accordingly but I would like to clean up the idle/low speed drivability.

    http://www.fordmuscle.com/forums/ind...d-engines.html
    Last edited by jrork; 11-18-2009 at 06:59 AM.

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    Quote Originally Posted by jrork View Post
    Hi guys. Is it really this easy??? I would like to get my Holleys boost referenced as I currently am PV plugged and jetted up accordingly but I would like to clean up the idle/low speed drivability.

    http://www.fordmuscle.com/forums/ind...d-engines.html
    Do your metering blocks have a ported vacuum port on the primary side? if so the last one i did i rerouted the power valves to use this Port. i have a tech Drawing saved on my computer i'll dig it up.

    Edit: i forgot to mention that ported vaccum is not controlling the powervalve function, explanation below.
    Last edited by [email protected]; 11-18-2009 at 12:09 PM.

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    gn7
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    Quote Originally Posted by [email protected] View Post
    Do your metering blocks have a ported vacuum port on the primary side? if so the last one i did i rerouted the power valves to use this Port. i have a tech Drawing saved on my computer i'll dig it up.
    If its a blower motor, you definitely DO NOT want to do that. Port vacuum increases with air flow thru the carb, as in increased RPM. This how vacuum secondaries are opened. Internally the same port. Soooo, on a blower motor, the faster the engine runs and the more air flow thru the carb, the more vacuum, and the more the power valve will stay SHUT. Not a good thing! Yo0u have to take it to the intake manifold. Don't expect a huge gain. Mostly just off idle. Zero effect at idle. Just remember the second the intake manifold pressure (vacuum) gets above the valve setting, its open. And that comes sooner than most think.



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    Last edited by gn7; 11-18-2009 at 12:01 PM.

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    Damn, I new i wasn't posting fast enough and gn7 already jumped to conclusions

    I didn't actually do mine this way, but it gives you a general idea of what your doing.




    Instead I plugged the Power valve passage in the bottom of the main body that matches up with manifold vacuum, also plugged the ported vacuum hole in the bottom of the main body. You can use lead shot or little brass set screws. Then in the face of the main body i angle drilled the passage from the ported vacuum hole to to intersect the cavity the power valve sits in.

    Or you can do it the way shown in the link you posted, i'm sure one way may be easier than the other depending on the components you have. and each will have the same end result. However if you use set screws the modification should be fairly reversible.

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    gn7
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    So there is alittle more to it than just hooking the power valve port to the ported vac circuit Because without clarifiying that, it was a disaster lokking for a place to happen.



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    Quote Originally Posted by gn7 View Post
    So there is alittle more to it than just hooking the power valve port to the ported vac circuit Because without clarifiying that, it was a disaster lokking for a place to happen.
    Yeah i know, there was a little lag time from the time i posted the teaser to the time it took me to formulate my response and upload the picture more caffeine will help that.


    Just realize it may have all been in vain because i think i remember that John has Proform main bodies. I know the way QFT does this is buy drilling straight through the side of the main body into the Power valve chamber. Just don't drill through the venturi. you still have to plug the passage on the bottom of the main body.

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    why don't you just tune the powervalves instead of blocking them? i hooked up a vaccum gauge under my 750's on my blown 475, took it to cruise level while watching the gauge and my a/f meter, kept in mind the vaccum under the carb at cruise and i put the appropriate p/valve in so when i stepped into it above cruise, it'd enrichen with the p/valves opening. worked for me, had a nice clean a/f ratio and purdy plugs.

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    gn7
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    Quote Originally Posted by IMPATIENT 1 View Post
    why don't you just tune the powervalves instead of blocking them? i hooked up a vaccum gauge under my 750's on my blown 475, took it to cruise level while watching the gauge and my a/f meter, kept in mind the vaccum under the carb at cruise and i put the appropriate p/valve in so when i stepped into it above cruise, it'd enrichen with the p/valves opening. worked for me, had a nice clean a/f ratio and purdy plugs.
    I believe he is trying to set it up so he can unblock them. He has PV plugs now. Don't know why your vacuum drops under you carbs when you floor it, but mine climbs, and I am running two 1050s. You would have to be running the blower pretty slow not to have a vacuum increase under the carbs when its WOT.



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    Quote Originally Posted by IMPATIENT 1 View Post
    why don't you just tune the powervalves instead of blocking them? i hooked up a vaccum gauge under my 750's on my blown 475, took it to cruise level while watching the gauge and my a/f meter, kept in mind the vaccum under the carb at cruise and i put the appropriate p/valve in so when i stepped into it above cruise, it'd enrichen with the p/valves opening. worked for me, had a nice clean a/f ratio and purdy plugs.
    If you turn that blower up you'll see enough vac. at the carbs at wfo to close the powervalves & burn up one of your pretty little plugs
    But of course , you already knew this , right?

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    gn7
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    Quote Originally Posted by Hass828 View Post
    If you turn that blower up you'll see enough vac. at the carbs at wfo to close the powervalves & burn up one of your pretty little plugs
    But of course , you already knew this , right?
    Yeah. like that the worst thing that could happen.



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    Thanks for all the replies guys. Just got off work.

    Yup, blown bigblock. Josh is correct, I have 2 850s that have Proform mainbodies.

    As I mentioned, I'm currently plugged and jetted up but would like to clean up my cruise ability and get some fuel mileage back compared to where I am now.

    I've seen carbs where they're referenced off the metering blocks and I've also seen them referenced off the plate but have never actually read what all is required to reference them. After looking over the links it sure LOOKs easy (but, I've made that mistake before ). Just not sure if it really is that easy and if folks have a preference of which approach is their favorite.

    Definately don't want to risk putting them in without referencing and have them shut at the worst possible time and as Hass mentioned, burn a plug ().

    Also, would the PV rating change when you swap pulleys? Go ahead and flame me, I can take it.

    Thanks guys................john

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    Quote Originally Posted by gn7 View Post
    Yeah. like that the worst thing that could happen.
    I thought the worst part was running around with underdrive

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    Quote Originally Posted by [email protected] View Post
    I thought the worst part was running around with underdrive

    Your pops and I have a competition as to who's running the bigger top pulley.

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    Quote Originally Posted by jrork View Post
    Thanks for all the replies guys. Just got off work.

    Yup, blown bigblock. Josh is correct, I have 2 850s that have Proform mainbodies.

    As I mentioned, I'm currently plugged and jetted up but would like to clean up my cruise ability and get some fuel mileage back compared to where I am now.

    I've seen carbs where they're referenced off the metering blocks and I've also seen them referenced off the plate but have never actually read what all is required to reference them. After looking over the links it sure LOOKs easy (but, I've made that mistake before ). Just not sure if it really is that easy and if folks have a preference of which approach is their favorite.

    Definately don't want to risk putting them in without referencing and have them shut at the worst possible time and as Hass mentioned, burn a plug ().

    Also, would the PV rating change when you swap pulleys? Go ahead and flame me, I can take it.

    Thanks guys................john
    I'd do which ever way you feel most comfortable with, the end result should be the same no mater which method you use. As far as tuning your power valve, your vacuum gauge is your friend.
    Last edited by [email protected]; 11-18-2009 at 04:19 PM.

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