"Tuned" exhausts systems.
Having witnessed 'quite a number' 
of dyno tests to optimize exhaust tuning on four stroke motorcycles, I have to say I was quite amused to read you can't tune an exhaust system for a four stroke engine. Take a look at the megaphone on a single cylinder 1950s racing motorcycle, or the tuned pipe lengths of any of today's factory supplied multi-cylinder motorcycle exhausts. They don't make some of the pipes longer just because they have extra tubing laying around 
Aircraft engines as mentioned by others are close to fixed speed engines, which means the exhaust would be easier to tune. The low rpm might result in relatively long pipe lengths, but you have to do the mathematics to figure it out. I'm sure the reason they didn't tune the exhaust on wartime Merlins in the modern fashion was because there was no space for the pipes.
It is interesting how the pipe configuration can alter the sound and noise level. A friend has a six-cylinder CAP aerobatic plane with a tuned system from the factory. Its remarkably quiet and sounds like an inline six racing car. Also interesting because its made from thin-wall inconel to save weight.
of dyno tests to optimize exhaust tuning on four stroke motorcycles, I have to say I was quite amused to read you can't tune an exhaust system for a four stroke engine. Take a look at the megaphone on a single cylinder 1950s racing motorcycle, or the tuned pipe lengths of any of today's factory supplied multi-cylinder motorcycle exhausts. They don't make some of the pipes longer just because they have extra tubing laying around Aircraft engines as mentioned by others are close to fixed speed engines, which means the exhaust would be easier to tune. The low rpm might result in relatively long pipe lengths, but you have to do the mathematics to figure it out. I'm sure the reason they didn't tune the exhaust on wartime Merlins in the modern fashion was because there was no space for the pipes.
It is interesting how the pipe configuration can alter the sound and noise level. A friend has a six-cylinder CAP aerobatic plane with a tuned system from the factory. Its remarkably quiet and sounds like an inline six racing car. Also interesting because its made from thin-wall inconel to save weight.
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This is what is stamped on the engine plate of my Lyc 360
160/165/170/180 HP at 2400/2500/2600/2700 RPM
The factory spec for my model lists take off distance of 300ft (at 2700rpm)with the CSP and 550ft (at 2500rpm) for the FP both on a Lycoming 360 C4F.
So a rough extrapolation would lead me to believe that if I can get an extra 100rpm static out of my FP (which PowerFlow say that it can do)which would increase my current 2500rpm static up to 2600rpm that should knock off at least 100 feet on TO distance which is huge for the type of flying I do and gets me pretty close to the CSP numbers without the added maintenance expense and weight.
If it pans out that way, I,d be a happy camper.
Edited to add, I understand the HP v RPM output calcs are not linear but I don't think my expectations are out of whack
160/165/170/180 HP at 2400/2500/2600/2700 RPM
The factory spec for my model lists take off distance of 300ft (at 2700rpm)with the CSP and 550ft (at 2500rpm) for the FP both on a Lycoming 360 C4F.
So a rough extrapolation would lead me to believe that if I can get an extra 100rpm static out of my FP (which PowerFlow say that it can do)which would increase my current 2500rpm static up to 2600rpm that should knock off at least 100 feet on TO distance which is huge for the type of flying I do and gets me pretty close to the CSP numbers without the added maintenance expense and weight.
If it pans out that way, I,d be a happy camper.
Edited to add, I understand the HP v RPM output calcs are not linear but I don't think my expectations are out of whack
piperboy84
You might get a little more than you think, as there is a double benefit. You not only get closer to the RPM for max HP, but you get more HP at that RPM as well.
MJ
You might get a little more than you think, as there is a double benefit. You not only get closer to the RPM for max HP, but you get more HP at that RPM as well.
MJ
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http://www.avweb.com/avwebflash/news...s221672-1.html
Power Flow Systems, maker of tuned exhaust system mods, has apparently had enough of the Internet harping of critics of its product and has fired a high-caliber “put up or shut up” salvo in reply. In an offer entitled "Shoot-Down at High Noon," Power Flow has said it is willing to come to any of the naysayers and prove its performance claims, while putting skin in the game. It will install one of its STC'd exhaust systems on an airworthy airplane, do before-and-after testing, and if the performance increase does not match or exceed Power Flow’s claims, Power Flow will make a $1000 contribution to the aviation charity of the critic’s choice. The kicker is that if the performance increase is true, the critic has to make a $1000 donation to the aviation charity of Power Flow’s choice. In its announcement, Power Flow clearly expresses its displeasure at what it refers to as self-appointed experts who attack the "dedicated men and women" of the company.
Power Flow’s offer sets forth the conditions of the test, including the company’s willingness to travel to any of the 50 states, inspect the airplane to be used and install (presumably temporarily) the system to be tested—all at its cost. The airplane will have to be one on which there is an STC for the tuned exhaust system, be airworthy and be operating within normal parameters. Power Flow says the critic may invite as many witnesses to the “Shoot-Down” as is desired. Results of the before-and-after testing are to be verified by an independent, impartial observer. Power Flow’s website sets out performance gains with the systems—for example, it calls for a 7-knot speed increase for the Cessna 177B Cardinal (power setting not specified) and a rate of climb increase of 125-300 FPM. Power Flow promises it will publish the particulars, progress and results of all challenges on its website
Power Flow Systems, maker of tuned exhaust system mods, has apparently had enough of the Internet harping of critics of its product and has fired a high-caliber “put up or shut up” salvo in reply. In an offer entitled "Shoot-Down at High Noon," Power Flow has said it is willing to come to any of the naysayers and prove its performance claims, while putting skin in the game. It will install one of its STC'd exhaust systems on an airworthy airplane, do before-and-after testing, and if the performance increase does not match or exceed Power Flow’s claims, Power Flow will make a $1000 contribution to the aviation charity of the critic’s choice. The kicker is that if the performance increase is true, the critic has to make a $1000 donation to the aviation charity of Power Flow’s choice. In its announcement, Power Flow clearly expresses its displeasure at what it refers to as self-appointed experts who attack the "dedicated men and women" of the company.
Power Flow’s offer sets forth the conditions of the test, including the company’s willingness to travel to any of the 50 states, inspect the airplane to be used and install (presumably temporarily) the system to be tested—all at its cost. The airplane will have to be one on which there is an STC for the tuned exhaust system, be airworthy and be operating within normal parameters. Power Flow says the critic may invite as many witnesses to the “Shoot-Down” as is desired. Results of the before-and-after testing are to be verified by an independent, impartial observer. Power Flow’s website sets out performance gains with the systems—for example, it calls for a 7-knot speed increase for the Cessna 177B Cardinal (power setting not specified) and a rate of climb increase of 125-300 FPM. Power Flow promises it will publish the particulars, progress and results of all challenges on its website
