Holley Power Valve?

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88bluestar
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Holley Power Valve?

Post by 88bluestar » Sat Sep 23, 2017 9:36 pm

On a 750 DP Holley with 850 base. Is it possible to plug off the primary side on a race engine?

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Re: Holley Power Valve?

Post by turbo2256b » Sat Sep 23, 2017 10:11 pm

there are power valve plugs. I often use them to help figure out jet sizes and power valve restriction sizes for best power yet retain fuel economy.
Plug it and you will need to go up about 6 to 10 jet sizes

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Re: Holley Power Valve?

Post by 88bluestar » Sat Sep 23, 2017 11:19 pm

I have 74's now but plan to plug it and start with 80's and go from there.

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Re: Holley Power Valve?

Post by mag2555 » Sun Sep 24, 2017 7:33 am

Just understand that it's the Jets that do the what's called the cruse range of throttle opening and the power valve restriction channel does the full throttle / max air flow metering.

Unless for race usage you motor leaves at within 1000 rpm of being in its power range I have never found that blocking the primary side helps at all, as very few motors rev instantaneously!

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Re: Holley Power Valve?

Post by turbo2256b » Sun Sep 24, 2017 10:08 am

mag2555 wrote:Just understand that it's the Jets that do the what's called the cruse range of throttle opening and the power valve restriction channel does the full throttle / max air flow metering.

Unless for race usage you motor leaves at within 1000 rpm of being in its power range I have never found that blocking the primary side helps at all, as very few motors rev instantaneously!

+1

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Re: Holley Power Valve?

Post by Coloradoracer » Sun Sep 24, 2017 10:22 am

Plug it....you can easily tune the carb to run well without it and it's one less thing to go wrong....you don't need it on a race engine anyway....

The power valve circuit only provides additional fuel under low vacuum conditions. The main jets provide the metered fuel for main circuit operation. If you have a low vacuum engine, the power valve will likely be open unless it's rated for very low vacuum. I think the lowest they go is 2.5. If I was to run one on my junk, it would be open all the time....I barely have 2" at idle.....by removing the valve all you need to do is increase jet size to compensate. This will have little effect on fuel economy since you're generally not running on the mains during part throttle operation, you're running on the idle and transfer slots.....
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Re: Holley Power Valve?

Post by Coloradoracer » Sun Sep 24, 2017 10:29 am

mag2555 wrote:Just understand that it's the Jets that do the what's called the cruse range of throttle opening and the power valve restriction channel does the full throttle / max air flow metering. **This is incorrect. The power valve is an enrichment device and opens when manifold vacuum drops below it's set point. It will close again when the vacuum signal goes back above it. The main jets provide the metered fuel anytime that circuit is active.**

Unless for race usage you motor leaves at within 1000 rpm of being in its power range I have never found that blocking the primary side helps at all, as very few motors rev instantaneously! **You will never see a difference by blocking the power valve. If it's set up right, the valve will be open at this point already. If you remove it, you compensate for the added fuel by going up in jet size.
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Re: Holley Power Valve?

Post by Firedome8 » Sun Sep 24, 2017 1:04 pm

88bluestar wrote:I have 74's now but plan to plug it and start with 80's and go from there.
Tune with and with out Pv ,,, and compare results,,,you should have changeable Pv restrictions. I personally use a powervalve in the applications I tune . what vacuum does the engine have in the return lane Or during a yellow flag ?

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Re: Holley Power Valve?

Post by mag2555 » Tue Sep 26, 2017 6:26 am

Could someone explain to me why it is that on the Holley site they list not one Dominator Carb that does not come with a primary power valve, could it be that the maker / designers off these Carbs know more then some here posting?

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Re: Holley Power Valve?

Post by turbo2256b » Tue Sep 26, 2017 11:35 am

Tend to use the Quick Fuel power valves as they are capable of flowing more fuel. I have never ditched a power valve in the primary a few instances in the rear. One thing I ponder from time to time is does an engine need 12.7ish AF ratio instantly when floored as FI can do or does the engine do best if the AF ratio as needed increases to 12.7 ish as a carb will do under wot. How about a large single throttle blade opening compare to several smaller ones at wot.

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Re: Holley Power Valve?

Post by levisnteeshirt » Sun Oct 01, 2017 10:44 pm

A power valve helps response ,, it also richens the idle circuit , some don't believe it ,, it does , not up for an argument

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Re: Holley Power Valve?

Post by jmarkaudio » Mon Oct 02, 2017 11:47 am

levisnteeshirt wrote:
Sun Oct 01, 2017 10:44 pm
A power valve helps response ,, it also richens the idle circuit , some don't believe it ,, it does , not up for an argument
IF the carb is set up and working correctly it will not have any affect on idle AFR. The video below is a 750, one of a pair set up for external boost referenced on the primary and secondary PV's. The video CLEARLY shows the O2 readings are unaffected when opening or closing the PV at idle. A test was also done at a higher RPM when the boosters were active and O2's are affected as the PV is intended to operate.

https://www.youtube.com/watch?v=jlp-Q_3 ... e=youtu.be
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Re: Holley Power Valve?

Post by pamotorman » Mon Oct 02, 2017 1:45 pm

jmarkaudio wrote:
Mon Oct 02, 2017 11:47 am
levisnteeshirt wrote:
Sun Oct 01, 2017 10:44 pm
A power valve helps response ,, it also richens the idle circuit , some don't believe it ,, it does , not up for an argument
IF the carb is set up and working correctly it will not have any affect on idle AFR. The video below is a 750, one of a pair set up for external boost referenced on the primary and secondary PV's. The video CLEARLY shows the O2 readings are unaffected when opening or closing the PV at idle. A test was also done at a higher RPM when the boosters were active and O2's are affected as the PV is intended to operate.

https://www.youtube.com/watch?v=jlp-Q_3 ... e=youtu.be
would this also be true if the idle transfer slot was open too far ???

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Re: Holley Power Valve?

Post by jmarkaudio » Sun Oct 08, 2017 12:18 am

If the butterflies are open too far to get it to idle then the carb isn't set up correctly, timing isn't correct for the engine, cam timing is off... something is wrong.
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Re: Holley Power Valve?

Post by My427stang » Sun Oct 08, 2017 10:15 am

jmarkaudio wrote:
Mon Oct 02, 2017 11:47 am
levisnteeshirt wrote:
Sun Oct 01, 2017 10:44 pm
A power valve helps response ,, it also richens the idle circuit , some don't believe it ,, it does , not up for an argument
IF the carb is set up and working correctly it will not have any affect on idle AFR. The video below is a 750, one of a pair set up for external boost referenced on the primary and secondary PV's. The video CLEARLY shows the O2 readings are unaffected when opening or closing the PV at idle. A test was also done at a higher RPM when the boosters were active and O2's are affected as the PV is intended to operate.

https://www.youtube.com/watch?v=jlp-Q_3 ... e=youtu.be
Good example, agree completely, only 2 ways a PV can affect idle

- Bad/leaking PV
- Airflow across boosters at idle due to incorrectly adjusted carb
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