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Hot!32/36 Weber Power Valve Questions

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ATD350
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2012/09/10 14:12:10 (permalink)
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32/36 Weber Power Valve Questions

I dont want to reinvent the wheel here, but as I have a progression plan for the current engine, I was wondering if anyone has ever played with the powervalve in 32/36 weber carbs?

Firstly, I am led to believe the standard powervalve opens at around 18" of vacuum. That sounds like a lot, basically meaning its open 90% of the time. if it was 10" or 12", that would make more sense to me. I imagine for a lot of big cam engines, it would be open all the time, including idle, as they would never have more than a few inches of vacuum.

Has anyone ever modified one to open at a lower vac point by cutting the spring down? I believe this is relatively common with the Jeep guys.

Secondly, I plan of using this carb for blow through and i reckon i can modify the PV to open only under boost or on the change from vacuum to boost, by placing just enough 'tension' (as opposed to pressure) on the diaphram, that even the most minor vacuum holds it closed, and boost pressure opens it.

Thoughts anyone?

Maybe I am overcomplicating this.....
#1


5 Replies Related Threads

    spigot
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    Re:32/36 Weber Power Valve Questions 2012/09/10 19:51:48 (permalink)
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    I would leave the carby alone and then add extra fuel enrichment via a boost ref Hobbs switch with injectors and rising rate reg. have a look at toohighpsi.com
    #2
    ATD350
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    Re:32/36 Weber Power Valve Questions 2012/09/11 08:05:06 (permalink)
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    Ultimately, the whole engine will go EFI.  but until then, especially with the very moderate boost levels I want to run, I would much rather just keep it all carby.
     
    My other car runs a Blow through Holley, with a boost referenced Power valve, and it is absolutely perfect, but it is a lot more serious than this.  With this engine, I am only looking to get maybe the same or marginally more power than I would with a big cam and twin 45's, just with better driving characteristics.
     
    Thanks anyway.
    #3

    jimmyd
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    Re:32/36 Weber Power Valve Questions 2012/09/11 19:59:56 (permalink)
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    If you're happy playing with holleys, I can do you a deal on a Weiland 4 barrel square bore manifold to suit the 2 litre....

    James
    #4
    Wozzah
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    Re:32/36 Weber Power Valve Questions 2012/09/13 21:47:06 (permalink)
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    ATD350

    I dont want to reinvent the wheel here, but as I have a progression plan for the current engine, I was wondering if anyone has ever played with the powervalve in 32/36 weber carbs?

    Firstly, I am led to believe the standard powervalve opens at around 18" of vacuum. That sounds like a lot, basically meaning its open 90% of the time. if it was 10" or 12", that would make more sense to me. I imagine for a lot of big cam engines, it would be open all the time, including idle, as they would never have more than a few inches of vacuum.

    Has anyone ever modified one to open at a lower vac point by cutting the spring down? I believe this is relatively common with the Jeep guys.

    Secondly, I plan of using this carb for blow through and i reckon i can modify the PV to open only under boost or on the change from vacuum to boost, by placing just enough 'tension' (as opposed to pressure) on the diaphram, that even the most minor vacuum holds it closed, and boost pressure opens it.

    Thoughts anyone?

    Maybe I am overcomplicating this.....

     
    I have never had the need to play around with the power valve.  Generally engines with large cams etc run different carbs like a 38/38, 40/40 or DCOE's as they have already reached the limits of the carb.
     
    Don't bother with the blow through, never seen a successful one.  The money and time you waste trying to make it work is better invested elsewhere.  If you're on a budget use an SU and set it up draw through for the moment, and inject it when funds are available. 
     
    Cheers
    Woz

    Mk1 RS2000 replica (IP hillclimb car) fitted with Ford Laser 1.8 DOHC (BP) Cossy cams, Webers, 230hp
    EB XR8 5sp, heads, cam, extractors.
    http://www.facebook.com/p...rmance/135194779879292
    #5
    Philtaz
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    Re: 32/36 Weber Power Valve Questions 2022/09/21 17:12:43 (permalink)
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    I know this thread is from the Late Triassic period, but I know that power valve problems will go on forever... 
    So I saw the reference to cutting the spring to weaken the resistance to vacuum pressure and I was going to try it to solve my problem with flooding under load.
     
    Then I thought of two things: Cutting a spring in front suspension actually makes it stiffer. A spring is like a v-shaped lever (in simple physics terms) so when you cut it you have a shorter lever to twist the spring material. Not sure if this would be the case with a progressive spring but was enough to make me think a bit harder. 
     
    Also, once you cut it, you can't uncut it.
     
    So I had a flash of inspiration and made an adjustable version which works!  Took me 5 minutes... 
     
    I drilled a small hole in the spring-guide tube and put a shortened screw in it. See pic.  
     
    I didn't have a nice little machine screw but turned out that this one works fine, just a bit scruffy looking.
     
    So what I can do now is rotate the spring so it compresses at the top, leaving the bottom half to do the work! It's very easy to adjust and you can easily feel the tension on the plunger.
     
    Weber should copy this and pay me a commission I reckon!
     
    Two things to watch is that the screw doesn't foul the float and that the screw doesn't press the piston. But the tube is quite thick and I had no problem getting the ugly screw to bite.
     
    Hope this helps someone else with the same issue... 

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