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Power Valve discussion - Forced Induction carbs

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powerband
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Power Valve discussion - Forced Induction carbs

Post #1 by powerband » Tue Jan 09, 2018 8:49 pm

Power Valve discussion on Forced Induction carbs from parallel post -' NEED HELP FINDING CARB'

The small passage from lower part of carb to the open back (not fuel side) of the power valve is what makes it work and the check ball with tiny spring under it is supposed to stay open to intake vacuum - it is there in case of a backfire which can 'blow-out' the diaphragm of the PV. So a backfire forces the ball to close against the spring pressure hopefully saving it from destruction. ( which usually wreaks havoc by flooding the carb)

With normal NA operation, power valve 'opens' / adds more fuel when vacuum/suction drops as you press the accelerator and the carb throttle plate opens to atmosphere. The PV's are rated in vacuum typically @ 2 to 9 hg. Obviously that is the opposite of what you need when you pressurize / blow-thru a carb.

One solution I tried was to epoxy seal the passage with the check-ball and drill through carb body and add an external reference port for the PV which can be referenced to intake vac before the Turbo or SC , controlled with elec. switch or other external means. Not too simple to mod or tune though. Some swear you can eliminate (seal) the PV circuit entirely and tune with jetting only.
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BUT:
Recently there has become available a Power Valve which is made specifically for blow-through operation and operates OPPOSITELY from normal - uses pressure in fuel bowl to open. This only requires sealing the check-ball port for blow-thru setup !.

I get mine on E-bay:

https://www.ebay.com/itm/Holley-Demon-Q ... 9d&vxp=mtr

Best explained in a post on the Turbo Forum (before the rant gets going):

https://www.theturboforums.com/threads/ ... st-2000077

'jet extensions' in the carb bowl are helpful to prevent sloshing/flooding with blow thru pressure, I don't alter the carb barrels accel pump "boosters/shooters" but do smooth the area with epoxy and sharpen casting.

No big mysteries with the simple 2300 2bbl , just get it sealed up pretty good, don't start with big jets or PV port enlargement. (I keep backing down jet size - even below typical NA operation). 350 cfm 7448 seems better suited for small six than 500 cfm 4412 version.

Parts, gskts, Jets, floats , sight windows, etc all availble at Summit , Jegs, etc
https://www.summitracing.com/search?Sor ... ey%20parts

(please add to discussion or corrections to errors :)

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haev fun
"Take time to stop and smell... The roadkill..."

Sick6Turbo
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Posts: 78
Joined: Sat Dec 19, 2015 12:53 pm
Location: Almond, Wi.

Re: Power Valve discussion - Forced Induction carbs

Post #2 by Sick6Turbo » Tue Jan 09, 2018 9:25 pm

:thumbup: All good stuff. Have a brpv from scs in an e85 600 build I did last summer and will be installing another in a similar build. Will use the vent tube extensions also. Should be testing one this summer, the other down the road.

"The Cure" has been excellent and rock solid dependable for me, but have been looking to clean up engine bays with internal mods and try new things. The brpv should transition fuel a littler better to help spool vs on/off with the cure. Although e85 turbo engines like their fuel and they like it now! :twisted:
Dale
79 F-100 turbocharged 300 rear mount 20 psi
Stock EFI bottom end, mild port carb head
12.44@106 1/4 mile in 2015

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