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RarlyL8 RarlyL8 is offline
Crotchety Old Bastard
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Join Date: Jan 2000
Location: Huntsville, AL
Posts: 13,556
You need to be past ~450whp before 1.625" primaries begin to perform better than 1.5".
If you have ported heads, or 38mm Carrera heads as in this case, it is better to compress that air down to 1.5" (~36.5mmID) for the sake of velocity and heat, which drive the turbo. The gains from larger ports are not lost if you use a conical transition to the primary from the head. This becomes even more important as the displacement of the engine is reduced due to the effect on torque.
RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 01-26-2010, 07:36 PM
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