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RarlyL8 RarlyL8 is offline
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Join Date: Jan 2000
Location: Huntsville, AL
Posts: 14,105
This has been discussed before and I posted to the thread but that was some time ago.

The direct answer to your questions is yes, the pancake manifold is asymmetrical in displacement to the cylinders. The center cylinders 2 & 4 are a straight shot and apparently more air is fed to them. It is not a lethal condition as these engines are set to run rich, which is an average of all the cylinders; 2 & 4 do not run lean, they are just not as rich as the others.

The easiest way to see this is to remove a heat exchanger and observe the color of each primary pipe. It is obvious. The 930 runs N/A the vast majority of the time so the little time spent on boost does not significantly affect what you see in the pipes. These are 70,000+ miles of accumulation.
Below are pictures of 3 different heat exchangers from 3 different engines:

To optimize the AFR you have to adjust the fuel feed to each cylinder which is not an easy task. This is what we have use to dial in the tune:

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 12-28-2014, 08:16 AM
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