Expansion chamber type exhaust for rotaties?
Expansion chamber type exhaust for rotaties?
(OP)
Here is a question that is nagging me; Why not expansion chamber type exhaust on a rotary engine, especially those with a peripheral exhaust port?
I was reading my old "Two Stroke Tuner's Handbook" by Gordon Jennings, and the chapter on exhaust pipe design. With a properly designed di/con type exhaust, a two stroke engines' output can be effectively doubled. (Assuming the engine can withstand the stresses, and attendant intake, scavenge & compression capacity is built in to support the output.) Rotary engines, especially those with peripheral ports, have significant port timing overlap similar to two stroke engines, thus my pondering about a di/con exhaust for these engines. The exhaust on rotaries have to be constructed out of high temperature materials as the exhaust temperature on these engines is quite high, so obviously, a di/con pipe couldn't be built out of thin wall mild steel, but for now this is a mental exercise.
The guys at Racing Beat, have always recommended straight primary header pipe, "as long as possible". (I've seen some rotary exhaust primary pipes over 50" long.) So there doesn't seem to be any real tuning going on via length.
What say you?
Robin Sipe.
I was reading my old "Two Stroke Tuner's Handbook" by Gordon Jennings, and the chapter on exhaust pipe design. With a properly designed di/con type exhaust, a two stroke engines' output can be effectively doubled. (Assuming the engine can withstand the stresses, and attendant intake, scavenge & compression capacity is built in to support the output.) Rotary engines, especially those with peripheral ports, have significant port timing overlap similar to two stroke engines, thus my pondering about a di/con exhaust for these engines. The exhaust on rotaries have to be constructed out of high temperature materials as the exhaust temperature on these engines is quite high, so obviously, a di/con pipe couldn't be built out of thin wall mild steel, but for now this is a mental exercise.
The guys at Racing Beat, have always recommended straight primary header pipe, "as long as possible". (I've seen some rotary exhaust primary pipes over 50" long.) So there doesn't seem to be any real tuning going on via length.
What say you?
Robin Sipe.





RE: Expansion chamber type exhaust for rotaties?
RE: Expansion chamber type exhaust for rotaties?
RE: Expansion chamber type exhaust for rotaties?
globi5: Yes, I am aware of the newer rotaries having the intake and exhaust ports on the side plates, I was thinking more of the racing rotaries with pure peripheral ports for the intake and exhaust, and the vast majority of on-road rotaries that have a peripheral exhaust port, with significant intake/exhaust port timing overlap.
I have a couple 4-port and 6-port engines to play with. Short of coupling one to the water brake and spending time on poking around various exhaust designs, I'm hoping this question had been asked and answered before. If not, then maybe it would make for an interesting techincal diversion. The racing engines with peripheral intake and exhaust ports have high port opening overlap. (Depending upon how agressive the timing is.) Some of these highly strung engines will not even start unless wound up to 1000+ rpm. They make fantastic power for the cubic inch displacement, but at high rpm and a razor thin powerband. Turbocharging the rotaries has allowed this timing to be made more conservative, but I'm curious as to why di/con exhaust was never applied to these engines in naturally aspirated racing applications. An answer to a question no one is asking?
Robin Sipe
RE: Expansion chamber type exhaust for rotaties?
Robin Sipe.
RE: Expansion chamber type exhaust for rotaties?
Regardless, there HAS been some work with expansion chambers. Most of it is kept secret, unfortunately.
Racing Beat's recommendations are old-think. The current fashion is primary lengths in the 13" range. Not too many people are talking about the collector shape, which is critical.