XR4Ti Archived Tech Articles
Post Date: Tue, 23 Oct 2001 Subject: Re: Bypass Valve and vacuum leak fixed! List: firstname.lastname@example.org >Please define "trailer hitching"! Ever tow a really heavy load on a trailer, and lift the pedal while driving a steady state?? The trailer alternately pushes and pulls back on the hitch, jerking the tow car around. With a loose load, and some wear on the hitch, it can REALLY make things interesting . . . Lifting the throttle on a turbocharged vehicle at decent RPM and boost can create a similar effect. Snapping the throttle shut forms a pressure wave that can rebound off the throttle plate so hard, it will lift it open slightly, relieving the pressure, letting them drop, and so on. Also, that reversion wave smashes in to the impeller wheel, sometimes with enough force to bend the vanes, and has been found to bend the throttle plate. Longer charge air paths, like air/air front-mount intercoolers, seem to make trailer hitching worse. The BOV/BV's stops this by opening when vacuum is sensed behind the throttle body. This relieves the pressure (to atmosphere in a blow-off valve, and back into the pre-turbo air system on a bypass valve), allowing the turbo to remain spinning at speed. Instant boost on the reapplication of the throttle. No damage or wear to the turbo.Back to the Tech Articles main page
Published by Chris Anglin.