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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Good info.

Plus the 993 had a decent runner length and much less restrictive metering system.

Long runner low end, short runner high end.

With our stubby runner - small port and restrictive metering assembly, der gut thinks any packing or increasing in VE from idle to boost onset is going to be modest.

With boost onset I am thinking we no longer are as worried about momentum created port velocity.

Also it seems Porsche only sacrificed the balance between the intake and exhaust on there CIS motors.

And, in 1978 when the CIS 3.0 SC got a 39mm intake ports the larger 3.3 turbo got tiny 32mm intake ports. Adjusted for motor size our ports are 40% smaller than the SC that was designed at the same time. (Later SC's were pulled back to 34mm being 30% larger).

I wonder if there is a noticeable off idle difference between the large port 8.5/1 CR SC and the small port 9.3/1 cars? The boost bump alone should be good for about 3-4% more power.

Lots to learn.

Old 02-02-2010, 09:09 AM
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