Shaker223 said "A BRPV is opened by boost and not vacuum."

This is at least partially right on stock Holleys, as the PV is always closed under a vacuum condition. But it is the lack of vacuum that opens it, not necessarily boost (although boost would certainly open it as well). I assume the BR part of BRPV means boost referenced. In such a setup is the PV itself modified in some way?

My problem with understanding this is that I still cannot see any way that vacuum would ever be present in the hat, or anywhere above the throttle plate in a boost setup. Guess I'm still missing something.
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Ribel

Check this out, another Hanger18 project: DIY boost referenced power valve with hand tools and a nickle. Explains PV theory too, good article with pics!


http://www.theturboforums.com/smf/index ... c=110547.0

The carb body is drilled and a nipple of some type is pressed or epoxied in place. The area you want access to is behind the PV in the main body. Make sure that area is completely sealed. The PV is modded in the below picture so the spring keeps the PV closed. Once boost rises and builds pressure in the chamber behind the PV it then opens the PV to richen the mixture. There are many different ways of doing this.

The PV channel restrictions need to be enlarged for boos as well. this is discussed in Hangar 18.

See here also:
http://slantsix.org/forum/viewtopic.php?t=42393&start=0



[img]><img%20src="http://farm2.static.flickr.com/1171/511 ... V"%20/></a>[/img]

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11.02 @ 120.56
http://www.youtube.com/watch?v=EAxRmoDgsdY
Chassis dyno
http://www.youtube.com/watch?v=wd6hFGzLJMc

Okay, now it's making a bit more sense. I'll read those suggestions!
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Vapolution vaporizer

The power valve normally works on a pressure differential between the carburetor body side of the valve and the float chamber side of the valve. Vacuum is just lower pressure. Vacuum doesn't pull the valve closed it's the pressure on the float bowl side of the valve which pushes it closed against the spring. If the valve is a 6.5 then there has to be 6.5" Hg more pressure in the float bowl than the manifold to close the valve.

I like the backwards valve that is sealed. Sealing one side of the PV makes it an absolute pressure device rather than a differential pressure one. If you have the back of the power valve (carb body side) connected to the carb hat then it's at the same pressure as the float bowl where is the differential pressure to make the valve open?

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Joshua

Good question. All I know is it works. I can see it on my AFR and the before and after modification brought the part throttle AFR down to 13:1 from 15:1+. Some guys have gone as far as to use an alternative pressure source to open the PV. There are lots of exaples on turbomustangs.com

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11.02 @ 120.56
http://www.youtube.com/watch?v=EAxRmoDgsdY
Chassis dyno
http://www.youtube.com/watch?v=wd6hFGzLJMc

Vacuum is anything lower then atmospheric pressure for a given elevation.
I think we may be answering apple questions with orange answers here. STOCK Holley's, particularly the more common 4 bbls like the 4150 or 4160, most certainly do reference vacuum for the power valve from the manifold. There is a hole just before the PV head side that drops down to the bottom of the carb, which senses the manifold state. Vacuum certainly DOES pull the valve shut and 6.5 refers to how much vacuum in the manifold will pull the valve closed. Pressure in the bowl of a stock unit (used in naturally asperiated engines) should never climb above ambient atmospheric pressure, and does NOT open the PV.

This is basic Holley physics guys....what's going on?
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Blonde_angel

We know...we are talking abouta boost referenced PV. Vacuum is not in the picture here.

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11.02 @ 120.56
http://www.youtube.com/watch?v=EAxRmoDgsdY
Chassis dyno
http://www.youtube.com/watch?v=wd6hFGzLJMc

The Holley is a right pain to work with. Go with a Carter/Edelbrock 500 to 600. They use needles through the main jet for power enrichment. They use springs to lift the needles when vacuum drops to zero. Under boost, the boost helps the springs to lift the needle and thus enrich the fuel air stream. Get a book on this type of carb. and get familiar with it, and you will find it a lot nicer than the Holley. In the end, It's all about tuning what you have.

OK, after saying this let the nay-sayers have their turn.

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Dr. L Dale Hynes PhD Applied Mechanics

The Holley is a right pain to work with. Go with a Carter/Edelbrock 500 to 600. They use needles through the main jet for power enrichment. They use springs to lift the needles when vacuum drops to zero. Under boost, the boost helps the springs to lift the needle and thus enrich the fuel air stream. Get a book on this type of carb. and get familiar with it, and you will find it a lot nicer than the Holley. In the end, It's all about tuning what you have.

OK, after saying this let the nay-sayers have their turn.

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Dr. L Dale Hynes PhD Applied Mechanics

Well, I actually have a Carter 600, but I'm a bit confused (heh) about one thing. If vacuum allows the springs to lift the needles for enrichment, how can boost do the same thing? Seems boost would keep the needles down. Are there any websites for converting Carters for blow-thru use?
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Cams sexy

See Here.

http://www.theturboforums.com/smf/index ... c=136075.0

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11.02 @ 120.56
http://www.youtube.com/watch?v=EAxRmoDgsdY
Chassis dyno
http://www.youtube.com/watch?v=wd6hFGzLJMc

Yea, it's an interesting article and I saved it, but it doesn't discuss referencing the needles.
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Ally