Re: decreas turbo outlet/exhaust to increase spool-up?? - Saab Performance Bulletin Board - Saabnet.com
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Re: decreas turbo outlet/exhaust to increase spool-up??
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Posted by Eric Law [Email] (more from Eric Law) on Fri, 23 May 2008 06:24:06 Share Post by Email
In Reply to: decreas turbo outlet/exhaust to increase spool-up???, drupchen, Thu, 22 May 2008 17:33:53
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I think you're misunderstanding the meaning of "decrease the exhaust port". You don't want to decrease the size of the port coming *out of* the turbocharger, you want to decrease the size *going in*... sort of.

The reality is this isn't a practical thing to do yourself. What we're really talking about is the internal geometry of the turbine housing on the turbocharger, as well as possibly the turbine wheel itself. I think you're much more likely to get good results simply by trying a smaller turbo unit, like a T25 from a non-Aero 9000, or even a GT17 from a 9-5 or 9-3. Of course there will be challenges there too, like connections that don't match.

One other thing you've got working against you is engine displacement. Given the same turbocharger, a larger engine will spool faster because the engine functions as a pump, and the larger engine pumps more exhaust through the turbo. So a 2.3 with the same turbocharger as a 2.0 will spool at a lower RPM.

The "de-hump" another poster mentioned refers to the exhaust manifold. If you remove the turbo and look inside the manifold, just behind where the turbo attaches there's a "hump" that quite obviously restricts the passage. Using a Dremel tool you can grind down this hump to make the exhaust flow better. Just be careful not to grind the manifold wall too thin!

Eric Law

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