Power Valve Selection: The Definitive Answer

Fuel and Air Systems

  1. mderoy340

    mderoy340 Well-Known Member

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    Try a white or orange cam up front, the pink cam is very slow.
     
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    • 12many

      12many Well-Known Member

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      Will do, thamks
       
    • AJ/FormS

      AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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      You're getting it done! congrats.
       
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      • yellow rose

        yellow rose Doctor of Thinkology.

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        THANK YOU for doing all the work for the naysayers and doubters. I learned the PV opening lie from a guy WAY smarter than me decades ago. I've been trying to help guys correct their stuff since then but it's damn hard to convince some people that Holley was dead wrong. So we're the clowns who repeated the lie in their carb books.

        Wait until you start trimming the main jet down to get the cruise A/F ratio as lean as it will take without a lean miss, and then you correct WOT fuel with the power valve channel restricters! You'll get incredible fuel mileage, it will make more steam in the middle and still roar on top.

        Thanks for doing the dirty work.

        Hopefully, more than one or two guys will revisit their tune ups and get the benefit of a correctly times power valve opening.
         
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        • AJ/FormS

          AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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          Yeah what YR said.
           
        • mderoy340

          mderoy340 Well-Known Member

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          If you race be careful with going lean on cruise, it may effect staging AFR. My street strip car will cruise at 15:1 but it runs to lean at the track when I stage at 2K foot braking, my 9.5 PV is closed. I removed the 73s and put the 74s back in up front and the car launched clean. Cruise dropped to low 14s and that's ok with me. Sometimes you have to compromise depending on how you use your car the most.
           
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          • yellow rose

            yellow rose Doctor of Thinkology.

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            Very true. Every situation has its little nuances. You may have to give up a little at cruise to get staging clean as you've clearly stated. And there nothing wrong with that.

            For me, when I was younger, hardcore and highly motivated, I would have had 2 tune ups. One for the track and the other for the street.

            Now that I'm old, less than soft core and highly unmotivated I'd do exactly what you did and would love it just as much.
             
          • 12many

            12many Well-Known Member

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            I'll definitely be trying to strike a happy medium with the tuning for sure, but will lean more for the power than the economy! Just focusing on the PV and the jets/pvcr circuits as a package has really made noticeable improvements. I have to work on this tip-in hesitation now, also check notes to see where I had idle mixture screws and how much the secondaries were opened. I believe I may have induced the issue somehow. A little back and forth action:eek: Thanks to all who've added to the topic here. :thumbsup:
             
            Last edited: May 13, 2019
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            • 12many

              12many Well-Known Member

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              Still working on slight tip in hesitation, getting there, but have some slow speeds around town bowl boilng to also remedy! Need some composite bowls! Heat shield not enough. Settled for the time being on 73 primaries, 10.5 PV, .052" PVCR, 83 secondaries.Aside from the above issues it runs great.
               
            • yellow rose

              yellow rose Doctor of Thinkology.

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              If you need a heat shield let me look around. There was one I was going to buy, but never got around to it. It seemed like the best deal at the time.

              I've screwed with phenolic and wood heat shields and never found much.

              Let me see if I can find that one I liked again.
               
            • MobileCustoms

              MobileCustoms Well-Known Member

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              Great thread and reading. thanks so much! I'm currently running on the richer side and I will be taking on my fine tuning very soon as well, so this is GREAT STUFF!
               
            • 12many

              12many Well-Known Member

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              My big issue with this van setup is with limited space between the engine cover and carb/air cleaner with the Action + intake I have at the moment, I have about a 1/4" extra room, gaskets included for anything, but the carb is sitting close to the intake either way. I've got an Air Gap and an M1 to play with, I was planning on running come next spring (along with other things planned) but I may just go ahead and slap it on, might help with the heat issue. Another option as well was running thin solid engine mounts to drop the engine a bit, but I've had to fabricate all the other stuff for it as it is now, and then it all will not align etc. It never ends
               
              Last edited: Jun 4, 2019
            • yellow rose

              yellow rose Doctor of Thinkology.

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              Ok, I found it. The nice thing about this is its THIN. I'm outta room too.

              Go to coolcarb.com and look at what he has. IIRC it's like 60 bucks or something for the full meal deal so it's not too terribly expensive.
               
            • mderoy340

              mderoy340 Well-Known Member

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              Look at the front fuel bowl and see how close it is to the upper radiator hose. I added a 90* heat shield I made to prevent the front bowl from getting cooked.
               
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              • qkcuda

                qkcuda Well-Known Member

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                I have the cool carb insulating spacers on mine and they work great. I say spacers because there are two thin ones that stack. The one directly under the carb is the same size as the baseplate. This gives you the necessary clearance for the linkage to swing.

                IMG_4485.JPG

                IMG_4486.JPG
                 
              • yellow rose

                yellow rose Doctor of Thinkology.

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                Did you have to trim some of the big plate away to clear your throttle linkage?
                 
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                • qkcuda

                  qkcuda Well-Known Member

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                  No, that was the way it came, it was designed for a holley. The salesman actually pointed out the passenger side linkage clearance issue and suggested the two thinner stacked plates, rather than one thicker plate.
                   
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                  • 12many

                    12many Well-Known Member

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                    Haven't had the van out for almost a month, too damn hot (mid 90s and humid) but got a heat shield installed. Used the same foil backed insulating mat as for the cold air box and doghouse panels. Attached to the underside of the airbox, it lays on top of the radiator hose/thermostat and on top of the intake around the carb base. Really keeps the heat from radiating to the carb bowls just letting it run in park as well as after its off, heat soaking will likely be much less. I also relocated (and insulated) the pressure regulator to keep that from boiling the fuel. You guys with all that underhood space got it easy!! The sooner these oppressive temps take a break I hope to really get down to fine tuning this carb and seeing the results of the PV change

                    IMG_20190707_103755.jpg

                    IMG_20190707_154532.jpg
                     
                  • AJ/FormS

                    AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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                    It looks like you don't have the V-can hooked up.....
                    and is the PCV hooked to the power-brake port?
                    What is that small full-time vacuum line hooked to, that goes to the front of the carb?
                     
                    Last edited: Jul 8, 2019
                  • 12many

                    12many Well-Known Member

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                    Pcv is hooked to the carb port, as it was with the Street Demon I ran. The other vac line runs to a vacuun guage. I've run the Street Demon with and without the vac can hooked up (ported) Haven't decided if I want to drill and install a nipple on the AED, or install a tee for the full yet.
                     
                    Last edited: Jul 8, 2019
                  • AJ/FormS

                    AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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                    Ok, I just have never seen the PCV hooked to the back port. I tried that once and the back cylinders went lean on me. It was not a 4-corner idle tho.
                     
                  • 12many

                    12many Well-Known Member

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                    A little update, for those that care, just got back from a good romp, got it nice and hot, ran it easy, did some primary only acceleration runs, a couple of "drop the hammer" at speed pass traffic runs, and a from a "stop and mat it" run. Engine temp at 190°. Great a/f readings everywhere (will have to do some proper plug readings asap) and runs fantastic otherwise. PV setup is a winner, jetting, idle bleeds etc. Just still have the slightest going lean hesitation at tip in. Could almost live with it but will still try to eliminate it Gonna tinker some more, best thing is after the runs, with the intake scalding hot, I can hold my hand on the carb as long as I want after all that. As Peter Brady once said "It Works!":lol:
                     
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                    • qkcuda

                      qkcuda Well-Known Member

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                      I just installed the 10.5 power valve and dropped the primary jets from 72 to 70. Went out for a long drive and my lean stumble at part throttle is gone. My cruising A/F ratios are now in the high 13's, so heading in the right direction. My idle A/F ratios did not change at all, maybe a touch leaner if anything, so the fact that I have a 10.5 power valve and 8.5 inches of vacuum at idle is not a problem. I will be headed on a 1 1/2 hour trip to Moparfest in the next two weeks, so I will leave it like this for now and see if I want to drop the jetting again.
                       
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                      • AJ/FormS

                        AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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                        there ya go
                         
                      • yellow rose

                        yellow rose Doctor of Thinkology.

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                        Thanks for the update. Can you remind us what power valve you started with?

                        Glad it helped you out. Late opening power valve timing can put a big hole in the fuel curve and you almost can't tune it out with pump cams and squirters.


                        EDIT: if you are still rich at cruise, drop the main jets a bit more to clean up the cruise. Then, when testing for WOT, it may be lean. If that is the case, don't touch the main jets. You open up the power valve channel restricters to make up for the fuel at WOT. Once you get the hang of it, you'll be helping anyone who will listen. Most won't.
                         
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