Vacuum Secondaries on Holley
Printed From: CorrectCraftFan.com
Category: General Correct Craft Discussion
Forum Name: General Discussion
Forum Discription: Anything Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=1422
Printed Date: December-04-2024 at 9:40pm
Topic: Vacuum Secondaries on Holley
Posted By: Jim_In_Houston
Subject: Vacuum Secondaries on Holley
Date Posted: April-06-2005 at 3:24pm
Believe it or not I replaced my 2V Autolite carb with a 4v Holley to increase economy and obtain performance. My thinking was that the 2v carb was probably rated around 350CFM and the 4V replacement is rated at 450CFM. Therefore, if I can run the boat in 2V mode the effective rating may be 225CFM. But, when I want to go fast I will have 450CFM available (in theory). (The only time I want to go fast is when some young kid in a new shiney boat tries to outrun me.)
I am considering installing a selinoid to unlock the secondaries with a flip of a dash mounted switch or a prox sensor near the 4V carb to detect exactly when the secondaries begin to open (so I can throttle back and keep the secondaries closed) but I began to think a dash mounted vacuum gauge may do the trick (and be a lot easier to install).
Question: Can a vacuum gauge be used to precisely detect when secondaries begin to open?
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Happy owner of a '66 and a '68 Mustang
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Replies:
Posted By: David F
Date Posted: April-06-2005 at 5:08pm
Jim:
I do not know the answer to your question. Although I have never really given it a thought, it seems to me that you can hear (deep roar) when the secondaries are open. Most of the time they will be closed unless you stab the throttle or are at or near full throttle.
Just my thoughts, nothing definative.
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Posted By: skyhawkflyer
Date Posted: April-06-2005 at 5:13pm
A vacuum guage could definately be used but it might be hard to tell exactly when the secondaries crack (begin to) open (unless your slamming the throttle). A vacuum drop of a specific value would be what your looking for, and the more you open your primaries (from idle) the more of a progressive vacuum drop you'll see (best idle is usually the highest vacuum reading you can possibly get). You would have to make some runs on the water to see when the secondaries open-get a visual on the secondary plunger movement and compare with the vacuum guage. You should be able to pick up a manifold vacuum (drop) that corelates with the secondaries opening. A slightly higher vacuum reading would represent the secondaries being closed. Try a manifold vacuum guage used for tune ups and let us know how it works, if it works well you could put a guage in your dash-but it probably would have a delay due to the length of vacuum line required to mount it. Do you have provisions to hook up a vacuum guage? Maybe somebody else out there has some idea's. Have I confused you yet?
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Posted By: jameski
Date Posted: April-06-2005 at 5:15pm
Jim, I like your thinking! This should be a VERY interesting thread. BUT, I don't know how much success you'll have running a standard vacuum-secondary Holley. The vacuum guage would tell you a lot, but I don't think it will quite do what you want. It should give you a good idea when your power valve opens and dumps gas; i.e. if your power valve is a 6.5, then you SHOULD be able to assume it stays shut until your vacuum guage reads below 6.5. The prox sensor would give you a better idea of when the secondaries open, but I think you'd find that as long as you're running the standard carb, you'll be opening the secondaries a lot more than you want to - I don't think it would be avoidable when pulling skiers, etc. A mechanical-secondary carb would make the theory a lot more plausible. If you had a carb set up with mechanical secondaries, you would stand a much better chance of accomplishing your goal - you could then use the prox sensor and try to only run on primaries.
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current boat
http://www.correctcraftfan.com/diaries/details.asp?ID=1977 - 94 Sport Nautique
previous boat
http://www.correctcraftfan.com/diaries/details.asp?ID=601 - 78 Martinique
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Posted By: 79nautique
Date Posted: April-06-2005 at 6:02pm
The vacuum guage should work fine without any real delay. You would see a slite delay on start up but once it is drawing vacuum on the whole system it should respond instantly. I would suggest a gauge that has the range that you are looking for instead of a universal one. That way the calibarions will be finer and it will be easier to see a drop in vacuum in smaller incruments. For instance say the max vac you would see is 15 in-lb I would look for a gauge 0-18 or 0-20 range verses one that went up to 0-40 or higher.
The proximity switch is a novel abroach and should work equally as well if not better becuase you would know exactly when the secondaries moved regardless of the vacuum reading. With the vacum reading there will be a slight range of a in-lb or two before the secondaries open.
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http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique
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