The "Cone of Reversion"
Has anyone built the (Paser Speed and Economy) anti reversion cone exhaust system?
What is the good the bad and the ugly. Thanks, BB
No but I know what you are talking about. I love Kents book and have read it cover to cover many times. I think his on target most of the time; i dispute some of his estimates for speed gained per individual modification, but that is the only criticism.
Not a criticism but some of his mods my be valid (like the anti-reversion cone exhaust port) but comes under the practical category. That is a heck of thing to do. If you have maintained Lycs, getting to the nuts with with a stock straight pipe is hard enough.
My logic says this mod is not worth it in light of better options like 4-into-1 "Headers" or collector system with "tuned" primary tubes. He never really got there with his exhaust. Also since Kent the Cafe Foundation has done extensive exhaust test and instrumentation on different exhaust systems on a 4 jug Lycoming. (
LINK)Go to their web site. They have the 3 part article on-line. Its very technical with lots of graphs but the conclusions and bottom line are easy to understand.
Here is a link to a anti-reversion cone test and dyno data that came up empty on a Harley Davidson (which is like a Lyc). It's possible they did not not fabricate the anti-reversion cone properly (internal baffle)? However it reinforces my opinion about this idea.
http://badweatherbikers.com/buell/messages/3842/16474.html
I never made an anti-reversion, but I do I remember one of my old Honda's, a 250 thumper (one cyl), had aftermarket pipes with a visibly tapered cone on the end that bolted to the cyl port. I don't recall if it had that little inner baffle? However I took that bike apart many times and don't recall the inner baffle that Kent shows in his book. So if all you do is put a cone on the end of the pipe with out the "ANTI-REVERSION" part, I suspect it does not do much.
HOWEVER cones or COANDA CONES or Coanda Nozzles at the EXIT end of the pipe DO WORK! However they are loud!!! The Honda 250 single I mention above also had something LIKE a Coanda nozzle at the exit. It was called a "megaphone" pipe for a reason. (A coanda nozzle is a cone that diverges than reverses at the very end.) However it does make more power. However with an airplane, consider the aerodynamic DRAG putting a megaphone outside in the slip stream. ANOTHER wrinkle is an exhaust that is straight or even tappers a little at the exit, may cause more back pressure and slight loss of HP, BUT in an airplane if the exhaust is pointing aft parallel with slip stream it gives THRUST.
With a diverging cone pipe exit (megaphone) or even Coanda nozzle you will lose that thrust you get with a straight or even necked down pipe. Kent claimed some impressive "jet thrust" with his experiments, but I'm not sure if his numbers his numbers where a little too enthusiastic. The problem with putting the pipes parellel with the belly to get more "jet thrust" is it beats the floor of the plane to death, so most angle the pipe and/or put a "down turn" exit.
Never found the "hot rod" reference Kent makes about anti-reversion, but looking at car headers, car shows, parts books, mags and info, I don't see this as a popular feature of any exhaust.
DOES that mean it does not work. No I get the principle, but you don't need "anti-reversion" if your pipe has HIGH Savaging (like a 4-into-1 tuned pipe setup).
Strike #2 is its just as much a pain to bolt up car headers as Lyc pipes. I suspect that CONE with internal anti-reversion baffle is just too much to fab and install verses the benefit, so many folks just do the cone part. Again with the LYC we don't have room for the nuts as it is. Why make greif for yourself.
A cool set of pipes is not cool if you can't bolt it up properly.
Like cars at least try to make sure the pipe and/or gasket matches the cylinder exhaust port as best as possible to avoid restrictions. Lyc exhaust are ROUND, gasket round and the pipe is round. To be honest I never really tried to "blueprint" this detail nor do I know if it needs it. Gaskets do have some tolerance, slotted holes which might make the gasket sit "proud" into the exhaust port if shifted. Some sloppy welding or slag might protrude into the pipe, which might need attention and a slight grind? I think Lyc did a good job getting a good match. With that said those nuts are a pain to get to; a cone would make it horribly harder to work with. As it is now I have several "custom" tools (wrenches and sockets I have put on the grinder) in my box just for the Lyc's exhaust pipe nuts.
"These are my opinions and does not reflect the opinion of management and 'reserve all rights' to be wrong."
