-------------- Original message from Lynn Hanover <lehanover@gmail.com>: --------------

Lynn,

  What is your opinion how power would be effected by splitting the exhaust again for two

mufflers after the collector ??...................

--
Kelly Troyer
"Dyke Delta"_13B ROTARY Engine
"RWS"_RD1C/EC2/EM2
"Mistral"_Backplate/Oil Manifold

 

Once the headers are joined in a well designed collector there is only a need to conduct gasses away in the lowest back pressure method available. Two mufflers would offer less back pressure than one of the same design, so two would seem to be better than one. I know that in some cases the collector might work better with a specific length of such and such tubing behind it, in general the collector is the end of exhaust tuning to about 80% of the whole system.

 

Some folks have noticed that they reach full power well before they reach full throttle. On the dyno you often see that this is a function of the butterfly position at full throttle. Too little or too much. And not just the open or closed stops, but over opening may get things spinning in one direction that helps power, and in another intake under opening does the job. So it turns out that full throttle is not the best thing all of the time. However, the dyno has 4 mufflers in parallel and very little back pressure.

 

Some of the systems I have seen on aircraft just makes me want to scream and attack with a hack saw right on the spot. But I have also seen green garden hose in the plumbing on airplanes. So I want to scream allot.

 

The Mistral exhaust I thought would be a masterpiece of clear thinking and execution. Not quite. After the loss of the Piper the pictures of the system were seen on another list. Hopeful would be the best I could say. Closed end pipes with holes out of each port. Enclosed with a big can. Execution was superb. Stainless or Incolnel with all great looking TIG welds.

 

But the number of pieces big enough to block the exit tube was, well everything could have and only one piece is needed. Was needed. The back pressure must have been huge. The big can then just collected whatever escaped from the engine. Sound wise it was effective.

 

For years, model airplane engines were throttled by a simple valve that closed down exhaust flow. Works great, no need to change the carb settings, simple, quiet. Get the picture?

 

The rotary is a 4 stroke Otto cycle engine, and all that means is that it has a specific number of operations in order to function. Beyond that it is just a big dirt bike engine. So like the model airplane engine and the dirt bike engine (2 stroke) it is sensitive to exhaust system tuning, and back pressure.

 

The intake tuning and lengths and diameters and Choke size and Throttle Body size are all important, and rely on the idea that during the opening intake cycle the chamber is at zero or low pressure. So the entire volume of the displacement is available for intake of the next charge. If the exhaust system is sub-par (and all of them are) there will be some leftover exhaust gas in the opening volume. How much is left determines how much intake charge volume can be inducted. 

 

In a racing situation the exhaust system will be 3 1/2" or 4" (mine is 4") This was on instruction from the engine builder (Daryl Drummond) to match the system he has on his dyno. The object is too have the escaping exhaust charge produce a vacuum in the chamber so the intake charge "sees" less pressure ahead of it than it "sees" behind it in the induction system. As though there were a little turbo pushing on the intake charge.

If you think racing has no application in aircraft do not read further.

 

The Renesis engine has no overlap, so I can have a very restrictive system with no down side. Really?

 

The lack of overlap is just a fact about the intake port and the exhaust port not being open at the same time. This is a real big help when at very low throttle settings and low speed/idle and so-on. It is a change made to reduce HC for California. In the Peoples Republic they have long forgoten why it was called the city of Angles by the Spanish before anyone lived there. 

 

The lack of overlap (in the Renesis) or the presence of overlap in other rotaries makes no difference at all in performance when exhaust back pressure is high.  In every case, the amount of exhaust gas pressure still trapped in the chamber when the intake port opens determines how much intake volume is available for the next induction cycle. 

 

So, if there is just one pound of pressure in the chamber when the intake port opens, the start of intake flow may be delayed, or worse, reverse flow into the intake runner may start things off in the wrong direction.

 

So the effect is what?

 

In effect the engine has been reduced in displacement. The intake port is wide open and no flow in going on for some number of crankshaft degrees, so the first effect is that intake port timing (Open point) is delayed. So the intake port is smaller. The total volume of induction is reduced because the chamber still has exhaust gas in it, So we have lost engine displacement (the engine got smaller). Not the hot rod dream.

 

The up side is that thus contaminated, the charge will burn more slowly and so mimics a higher octane rating along with lower nitrogen oxides. Also lower combustion pressure and lower torque. So little loading on bearings. 

 

So, a intake system designed at one end of the building and working perfectly on their dyno must include the exhaust system designed at the other end of the building that is quiet as a mouse in slippers but was never on the dyno with the production intake, or run to destruction in a test cell.  

 

In any case the intake volume required by the engine at any particular RPM, may be available well before full throttle is reached. 

 

With a high degree of probability..................

 

Lynn E. Hanover