Data
Mr. G
You have dates, but no dyno. Paper is great for theory, but the dyno is king. Cafe or anyone else making horsepower claims in aviation have yet to display good old "dyno trashing". On the 40 year thingy, got my first drag strip record in '64. I guess I must qualitfy for the 40 year hot rodder. Yes, we were aware of it back then, and like the rest on my compatriots, none of our circle had a dyno. It was caluclation and conjecture, and hopefully good ET on Suinday. Then came weather, but that's another story.
What we have in aviation is a lot of figures, conjecture and no dyno comparisons.
As another member stated pipe lenght calcuilated to 77 inches in length. and that makes most sense since we are dealing with slow reving engines. No matter how we slice it, a pipe will do nothing more that place power at some point of the engies operating range.
I read nothing about the more important component that indeed do create horsepower, such as piston designs and clearances that rival locomotives, fuel air induction, camshaft designs, cylinder head flow (for which AV engines are abismal). These components/areas are the power brokers, not the pipe. It's no wonder that Lycoming has little or no data in this area, and I doubt that anyone in aviation does, Power Flow not withstanding.
On the Power Flow system, I was active in one of the Cherokee groups. By their own statement, they compared a Cessna 172 with a high time Lyc 320 to a Cherokee 140 with a freshly OHed 320. The Cherokee won. I am not exaggerating, this was their claim. They "calclated" that the difference of climb and SL performance, that the Cherokee has at least 23% more power.
Further in one edition of Cherokee Pilots Magazine., their own comparisons of their Cherokee with and without hardly varied more that 2 to 5 mph. Climb 50 to 60 FPM, and top speed same as cruise 2 to 3 mph. None of the figures were within to Piper specs, and a stock Cherokee 140 from a member did indeed perform as specified by Piper without their system.
In effect the claimed increase was no where to be found. As time went on, several owners admited that there really was little if any gain.
Tuned exhaust systems will work in unison with other components, including compression, pistons designed, tolerances, flow, combustion chamber design, camshafts, and associatred valve train, etc., but merely bolting on a pipe ain't gonna do it.
One more small item. Power Flows claim of power claim this "vast" increase in power for a 140 Cherokee. When comparing a Cherokee 140 and 180, we find identical airframes with slightly, very slightly higher gross weight for the 180. The 180 has 40 more cubic inches of displacement, and 30 more real horsepower than the 140. Due to the larger and higher pitch of the 180, it is a grandiose 7 mph faster, climb is 125 fpm more. Now were talking about a larger and more m powerfull engine. After all is dasi and done, a 140 equiped with this pipe cannot match a 180, 23% increas equated to 184hp.
Am I a doubting Thomas, you betcha. Untill I see a dyno in the midst, I will continue to be one. After 40+ years of hot rodding, this "argument" isn't anything new, but a lot of fun, to be sure.
T88