2nd Generation Specific (1986-1992) 1986-1992 Discussion including performance modifications and technical support sections.

twin scroll?

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Old Jan 9, 2006 | 03:22 PM
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rotary downshift's Avatar
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From: Performance Improvements
twin scroll?

can anyone tell me what the twin scroll does or doesnt do ?.. and what benafits would be obtained by removing it and portin the turbo runners to match? i realy wopuld like to understand this ..
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Old Jan 9, 2006 | 03:54 PM
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NZConvertible's Avatar
I'm a boost creep...
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The turbo is a twin-scroll design (two seperate exhaust passages in the turbine housing). There's a flap in the exhaust manifold that can block one of those passages, which increases the exhaust gas velocity in the other one. Doing this at low rpm makes the turbo spool up quicker, reducing turbo lag. The flap is closed below 2700rpm and open above that. It's operated by manifold vacuum and controlled by an ECU-switched solenoid valve.

On a stock turbo with will only be minimal top-end gains from removing the flap from the manifold, and an increase in low-rpm turbo lag. I wouldn't remove it unless you had an upgraded turbo.
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