Jim Rosinski wrote:

My interpretation of this is that it might actually be possible to
get
more than rated horsepower. Specifically, if the "tuned" system does
a
better job than straight pipes. How likely is this? Dunno.


Not very likely. The tuned system is making up for huge
inefficiencies in the factory exhaust system. The straight stacks used
for testing are pretty close to ideal. The tuned pipes are designed
to reduce backpressure by having the exhaust pulse from one cylinder
lower the pipe pressure as the next cylinder opens it's exhaust valve.
With short stacks, backpressure is not much of a factor.

In order for a Powerflow to show gains in horsepower, you need to
start with a restrictive exhaust system. For example, they showed
excellent progress with the exhaust system that was fitted to the early
Cherokees. When they were developing a system for the later model
Cherokee 180s, they found that the factory system was pretty good
already and that they couldn't really improve performance significantly
by installing their tuned system.

John Galban=====N4BQ (PA28-180)