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Hi,
I haven't seen anybody mention the biggest performance problem of CIS (I have 2 CIS cars and I like CIS for its simplicity and robustness):
It meters fuel more or less by air mass. It measures air mass by putting a circular plate square in the air stream. The aerodynamic resistance of that plate is (more or less) proportional to the air mass flow and used to move the plunger. But that plate is also a big intake restriction. Basically the volumetric efficiency of the engine is limited by it, no matter how well you make it breathe downstream. And as the plate has basically the same aerodynamic resistance in either flow direction (unlike a flapper style MAF sensor) it is sensitive to intake reversion. Porsche (and other CIS users) use the rubber boot between throttle body and CIS plate throat as pulse damper, but that works only so far. I actually measured the effects of that rubber boot on AFR when switching between a new one and an old and hardend one, and they were measurable at certain RPMs. The old boot was still airtight, so it was not leaks but more of the intake pulses getting to the plate.
Regards,
Klaus
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