exhaust systems / myths ??

[Russell]

can recall many times over years that " the correct back pressure " is extremely important for ultimate engine performance........so......we gyro buffs, bolt on our automotive engines, bend up a pipe or 2, attach "a muffler".........go fly. About the only concern we have is noise minimisation.So............just what are really achieving here........my view, maybe, maybe not, we are running a poorly performing power plant that is begging for better breathing / exhausting, if all the dots align, then we achieve better efficiency and better fuel economy...........i know of 1 guy who bolted his engine into same brand car, and put the car over a dyno, the results were interesting.........hence this thread.( he remade his exhaust with "tuned lengthed" headers, this alone was more positive ) putting his car over the dyno again and again showed him results of his mods. Another guy took his exhaust off his rotax 4 banger, and got a tuned system via yank land and is extremely happy with a better engine.

[asra]

i agree a bigger exhaust is not nesiceraly better the goal neads to be a ballance between exhaust and intake velocitys matched to camshaft duration in my experiance(building race car engines not gyros) most gyro motors lack in the cam department you would nead a valve duration up arround 300 degrees for a sustained 4500rpm if you notice a 912 idles high 1800 rpm this is to overcome the cam which is designed for eficency at +5000rpmjust my thoughts anyway

[mad max]

You"re right guys, I sent my ea81 cam to a cam place with a note attatched asking "please modify for max. power at 4,500 to 5,000 rpm for gyrocopter" I fitted it plus an ea82 intake manifold and carb. and some tuned pipes, the dimentions given by a rev. head. I found I had to tie up the advance weights, leave off the vacume unit hose, and set the timing a long way advance. Once I got it right I had an aeroplane engine. Its been going for many years. Has a ton of grunt. I lost about 50 rpm when the ground wuffo yuppies insisted I fit a hot dog.

[asra]

not to sure about hot dogs a modern motorcycle design of muffler makes good hp and low weightsomtimes all you nead to do is change the exhaust frequency to stop the sound traveling the actual total db not so important or fit a turbo they kill a lot of noise

[tonydenton]

max, so what did you have before the hot dog ?? everyone said it wouldn"t work but i

[mad max]

Before the hot dog I had straight pipes (two into one) of the dimentions given. I then fitted a hot dog, trying to maintain the same length and I lost 50 rpm. I asume the hot dog upset the tuneing a bit. Haven"t worried about it as there seems to be plenty of torque.