Whipple bypass valve stuck open?

[moffetts]

I drove my car last night and I noticed that I was not getting much whine, especially at low throttle (and I have the sound tube mod so normally it is quite loud at WOT and I get a little bit of a whistle at low throttle) and the car is definitely down on power. I am seeing about 2 degrees of timing advance at WOT which is normal, so I don’t think there’s a fuel issue. I am wondering if I have a stuck bypass valve, since that is a relatively common issue that can cause these symptoms. I did recently do the stage 1 > 2 upgrades but the car ran like a scalded rat up until recently, so I don’t think there’s an issue with the install (or the o ring on the bottom of the blower where it meets the manifold, more specifically).

As far as the bypass valve is concerned, I would like to test it before I take the blower off (again) and risk that not being the issue. Is hooking a vacuum pump up to the vacuum hose going into the bypass valve the best way to test it?

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[Roush05]

I don't know the layout of the whipple but I'd check for a vacuum leak somewhere. Not sure if the whipple has a vacuum manifold but I'd look there and then go out from there.

 

[Burkey]

I drove my car last night and I noticed that I was not getting much whine, especially at low throttle (and I have the sound tube mod so normally it is quite loud at WOT and I get a little bit of a whistle at low throttle) and the car is definitely down on power. I am seeing about 2 degrees of timing advance at WOT which is normal, so I don’t think there’s a fuel issue. I am wondering if I have a stuck bypass valve, since that is a relatively common issue that can cause these symptoms. I did recently do the stage 1 > 2 upgrades but the car ran like a scalded rat up until recently, so I don’t think there’s an issue with the install (or the o ring on the bottom of the blower where it meets the manifold, more specifically).

As far as the bypass valve is concerned, I would like to test it before I take the blower off (again) and risk that not being the issue. Is hooking a vacuum pump up to the vacuum hose going into the bypass valve the best way to test it?

You can test it with a vac pump OR just get someone to give it a rev and watch the valve.
It should snap shut very quickly when they stab the throttle.
From memory, the bypass should hold open at 11” of vac. Could be wrong on that figure but it’s certainly 11-16”
Might be worth contacting Whipple efforts the exact figure if you’re going to test it that way.

 

[moffetts]

Thanks for the insight, guys. I took the TB off last night to get better access to the bypass valve and observe the butterfly opening and closing inside the supercharger itself. I was able to apply some human-powered vacuum to it, at lest, and it does open and close as expected. I put everything back together and took it for a flog and it drove as I'm used to. I didn't really change anything aside from reseating the vacuum line to the manifold and bypass valve and reinstalling the inlet piping and TB, so I'm not sure what is going on at this point. I'll keep a close eye on it.

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