[Subscribe to Daily Digest] |
An how does ones judge or measure such things. A basic steady state dyno will not help.
When you intall a new performance gadget and go out and to evaluate, in your enthusiasm with repeated boost runs you are getting the turbo very hot, which improves power. If it is summer, you will get a heat soaked intercooler which will reduce power. In cooler weather the overoff effect of hard driving will be better preformance.
But folks with dump valves do say that they do provide better performance. But this will be only in the boost recovery during shifts. This benefit would be apparent if your style of driving would take advantage of it.
Then there are bypass valves that are leaking or bown. These missmatched or damaged valves are not allowing boost to be achieved. So replacing these with any unit that does not leak will improve performance. For some it is an issue of reliability. They do not want another rubber and plastic unit, or a metal one with a rubber diaphragm.
Not all bypass and dump valves have the same flow capacity. One that dumps more air will work better. A bypass valve that dumps to atmosphere will flow more. With the Saabs, discharge through the 1" long pipe may not be fast enough.
Fitting an high performance bypass valve or dump valve would not be the first thing you do to improve performance. I would put it several upgrades later. Until you increase boost, there is probably no need at all. Viggens are an exception, the higher sprung factory bosch plastic units often don't hold up.
And a note about true piston bypass valves and diaphragm types. On the diaphragm types, the boost pressure acts on the diaphragm and the pressure connection comes in at 90 degrees to the valve plug axis. With piston type units, the boost pressure is on the face of the end of the piston. The pressure connection is co-linear with the piston axis. So at first look, the piston type unit may appear to be connected backwards if you are used the look of the orientation of the factory unit. This means that some folks will connect them backwards.
Overall, the bypass style valve should work better if it is designed to flow enough. I say this because by defintion, a blow off valve is designed to close much sooner to avoid any reverse flow of air. So it should be able to be more complete in its action. It should allow for more turbo spin at part throttle befroe going on boost. Overall there are too many variables to make any truely definative statements, except to say that when upgrading the system, the OEM valve can become a problem.
, Mon, 13 Nov 2000 02:22:54, Mon, 13 Nov 2000 13:38:11
, Tue, 14 Nov 2000 07:00:47
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
