[Main Performance Bulletin Board | BBFAQ | Prev by Date | Next by Date | Post Followup ] Member Login / Signup - Members see fewer ads. - Latest Member Gallery Photos Er, no... Like This Post: - Subscribe to Daily Digest for this Bulletin Board Posted by Justin VanAbrahams [Email] (#32) [Profile/Gallery] (more from Justin VanAbrahams) on Sun, 30 Dec 2001 04:03:27 In Reply to: I am not so sure about this........, SteveW, Sun, 30 Dec 2001 01:04:16 Alert me when someone posts in this thread: Members do not see ads below this line. - Help Keep This Site Online - Signup

The bypass valve on a Saab dumps the pressure charge to the low/intake side of the turbo, where it is sucked back into the intake stream. The intake charge most certainly does not go back out the filter... that would be damn near impossible. The "whooshing" noise probably shouldn't be there... if you're getting one on a stock turbo, there's a good chance it's cause your bypass valve is shot and your intake charge is slamming into the compressor wheel. On some cars, you *might* get a "pffft" noise or a slight whistle or even a hoot - that's caused by the air passing through the bypass valve. On a dump valve (aka blow-off valve, whatever) you may get a whoosh, a pfft, or a whistle depending on what unit you choose.

All of these units function on one principle, and that's vacuum. If any of them are open during part throttle or anything less than near full vacuum then something is broken or not working right. The Bosch units are calibrated to open at ~80% full vacuum on a 16v car. At idle, there is not enough vacuum to open even the stock unit. Some of the aftermarket units are adjustable as to when they open, and some include a facility to be held closed when boost is present. Regardless, they should never be open at part throttle...

-Justin

posted by 66.123.95.1...

• Could someone enlighten me on dump valves..., Trevor B., Sat, 29 Dec 2001 21:12:22
  • Re: Could someone enlighten me on dump valves..., Simon S, Sat, 29 Dec 2001 22:58:19
    • I am not so sure about this........, SteveW, Sun, 30 Dec 2001 01:04:16
      • Er, no..., Justin VanAbrahams , Sun, 30 Dec 2001 04:03:27 <-- Viewing This Message
    • Well it is CIS, but maybe the same principal... n/m, Trevor B., Sun, 30 Dec 2001 00:00:07
  • Re: Could someone enlighten me on dump valves..., Quinn S. Kurz, Sat, 29 Dec 2001 22:31:22

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