[s-cars] By-pass valves

[John Cody Forbes]

They have a diaphragm and spring that draws them open when there is vacuum on the small line on top (like when the throttle is closed). Some, but not all, have enough spring on them that they need vacuum on the diaphragm PLUS a little bit of pressure on the bottom of the piston to push it open.

-Cody (mobile)

On Aug 11, 2010, at 5:56 PM, Eric Sanborn <esanborn at gmail.com> wrote:

> I might be misunderstanding what you were testing, but they should only open
> during boost.
> 
> On Aug 11, 2010 5:12 PM, <dgraber460 at aol.com> wrote:
> 
> 
> List-et-al;
> I have been chasing a full throttle issue on my 3B'd URQ for a few months
> now. The symptoms have been a flattening and lack of power under full
> throttle. My boost gauge has always shown full boost at 19-20, and it throws
> no codes. I started to notice the moaning (not whooshing) noise when off
> throttle, which I had heard before and found to be an aluminum bypass valve
> that needed cleaning.
> Since it had been running an OEM Bosch plastic valve, I pulled the Forge
> valve off the S-Car and cleaned it up and installed it. On the drive this AM
> it seems to have cured the issue. Time will tell if total cure.
> The question I have is that I tried to test all 3 valves that I have while
> messing around last night. I have 2 plastic, and 1 Forge valve. I hooked up
> a vacuum pump that pulls 14 lb hg to each valve individually and _none_ of
> them would pull open. Then I used my little Mighty Vac hand pump and the
> Forge valve would pull open and stay. Neither plastic OEM valve would open
> with either test. Does this indicate both OEMs are toast?
> I assume the vacuum pump did not have a check valve and therefore could not
> "build" vacuum as the Mighty Vac did, thus letting the valves flutter but
> not pull open. Sound reasoning?
> Also - is there a recommended lubricant that keeps the aluminum valves
> happy, and functional, or should they remain dry?
> 
> Dennis
> Denver
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