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Unread 02-08-2008, 12:23 PM
dtilman dtilman is offline
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Default Cessna Short Stack vs. Classic - difference?

The only measurable performance difference between the short stack vs our classic (long pipe) are found only on the Cessna 172 and 177. This does not apply to Grummans and Piper installations.

The performance differences are subtle and only seen in three areas, which the average customer/non test pilot may not even notice.

1) The RPM gain on the C172 with the classic we measured at 65 RPM on our test aircraft. The short stack showed 58 RPM. Slight loss in performance, but hard to see.
2) The classic exhaust system allowed aggressive leaning - lean of peak operations for fantastic fuel savings. The reality is that the vast majority of our customers don't use lean of peak operations so this is an unrealized benefit.
3) We have a report from a customer who routinely flew their C172 at 15500 MSL Feet with the PFS classic. They converted to the Short stack and reported the loss of Lean of peak leaning and they were unable to get above 14000 MSL - so we have a reduction in the gain in service ceiling.

From an installation and maintenance aspect, the short stack for the Cessna models wins in most areas:

The short stack is: 1.5 pounds lighter, takes one hour less to install (average) and does not require you to remove the lower pipe to remove the cowling.

From a noise perspective:
The noise on the ground in the cabin with the short stack is a bit more "sharp", but in flight our customers have told us the noise appears to be lower than with the classic system. This is likely because the short stack points down and is 2 feet forward of the cabin. The classic pipe is 2 feet closer to the cabin and pointed straight back (aft.)

Grumman and Piper short stacks are approximately the same length as the "classic" systems they replace, so there is no change in tuned length or performance. The Cessna Short stack is approximately 40% of the tuned length of the classic pipe, hence the slight drop in performance.
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Power Flow Systems, Inc.
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