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Old 07-02-2013, 09:10 PM
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Holley carb question

Ok one more for the night. I have a Holley 750 dp four corner idle. My question is it has two power valves would it be wise to block of the secondary power valve and up the jet size? For a street car that is driven hard?

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Old 07-02-2013, 09:21 PM
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why are you thinking of blocking the PV? If the reason is good,then do it.
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Old 07-02-2013, 09:38 PM
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Quote:
Originally Posted by 355/72camaro View Post
Ok one more for the night. I have a Holley 750 dp four corner idle. My question is it has two power valves would it be wise to block of the secondary power valve and up the jet size? For a street car that is driven hard?
The secondary pv is sometimes blocked if the G-force of acceleration is such that the pv is uncovered, like in drag racing. Street vehicles seldom have that problem, and retaining it can potentially help drivability. So unless you are driving hard all the time, I'd leave it in. Be sure it's calibrated correctly.
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Old 07-02-2013, 09:38 PM
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To be honest I want ease of tuning. I run a large cam with hardly any vacuum.
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Old 07-02-2013, 09:49 PM
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what do you call a large cam? There are several things for holley carbs, to improve tuning
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Old 07-02-2013, 09:54 PM
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Quote:
Originally Posted by cobalt327 View Post
The secondary pv is sometimes blocked if the G-force of acceleration is such that the pv is uncovered, like in drag racing. Street vehicles seldom have that problem, and retaining it can potentially help drivability. So unless you are driving hard all the time, I'd leave it in. Be sure it's calibrated correctly.
Thanks for the tip but I thought the primary pv was the one to worry about. And excuse my rookie knowledge but at wot or secondary opening I would be hard on the throttle why would there be a need for it? Also isn't the power valves job to enrich off idle? I don't want to sound stupid but I don't know much about dual pv holley carbs.
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Old 07-02-2013, 10:18 PM
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Quote:
Originally Posted by 355/72camaro View Post
To be honest I want ease of tuning. I run a large cam with hardly any vacuum.
If the carb's set up correctly, you may not notice much if any difference between w/pv and w/o pv, except that the secondaries can be too rich under some conditions w/o the pv. That depends in large part on how you drive. Most street vehicles can see some benefit from using a pv.

Quote:
Originally Posted by 355/72camaro View Post
...I thought the primary pv was the one to worry about.
You need to worry about them both, as far as calibrating them to match the needs of the engine. But the primary side is obviously used more than the secondary side, so you'd likely notice it more if it was bad or was the wrong part.

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...at wot or secondary opening I would be hard on the throttle why would there be a need for it?
In a case where the throttle was WFO and the engine fully loaded (causing the vacuum to drop below the opening threshold of the pv), you wouldn't have a need for a pv. If you were to run w/the secondaries partially open (or even fully open) but the engine wasn't loaded enough to drop the vacuum below the opening point, then you could benefit from a pv because it wouldn't add fuel when it wasn't needed. Lean is fast (within reason). Rich, not so much.

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Also isn't the power valves job to enrich off idle?
As you might have figured out after reading the post so far, the pv adds fuel when the engine is under a load, causing the vacuum to drop. So yes- it richens off idle so to speak, but not unless there's a demand for it that's indicated by the amount of vacuum the engine is making along w/the throttle position.
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Old 07-02-2013, 10:23 PM
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why worry, they are made to be run. gas in oil ?
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