X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from ispmxmta05-srv.alltel.net ([166.102.165.166] verified) by logan.com (CommuniGate Pro SMTP 5.0.4) with ESMTP id 886725 for flyrotary@lancaironline.net; Sat, 17 Dec 2005 21:58:26 -0500 Received-SPF: pass receiver=logan.com; client-ip=166.102.165.166; envelope-from=montyr2157@alltel.net Received: from Thorstwin ([4.226.237.5]) by ispmxmta05-srv.alltel.net with SMTP id <20051218025740.FJZA8731.ispmxmta05-srv.alltel.net@Thorstwin> for ; Sat, 17 Dec 2005 20:57:40 -0600 Message-ID: <002601c6037e$d5808490$05ede204@Thorstwin> From: "Monty Roberts" To: Subject: Exhaust tuning Date: Sat, 17 Dec 2005 20:57:49 -0600 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0023_01C6034C.8A333F50" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0023_01C6034C.8A333F50 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Well, I have nothing better to do on a Saturday night so I will subject you = all collectively to my random thoughts (assuming you read this) I have been trying figure out how to cram a muffled, tuned, road-race, = exhaust system under my (tight) cowl. No easy task. I am going to be running a Pport NA high compression motor.=20 The prevailing wisdom is to use 10-26 inch primary pipe into a collector = to a 24 in megaphone that goes from around 2 in to 4 in dia. over it's = length. After looking at this thing for so long my head hurts I have concluded = that the rotary shares aspects of a two cycle and four cycle but is = nothing like either in terms of exhaust system tuning. Two cycle recips can use a divergent/convergent cone type expansion = chamber. The timing of the pulses alternately draws gases out of the = combustion chamber to assist scavenging to the point of overscavenging = at the operating point, and then "stuffs" the overscavenged mixture back = in at the last moment as the port closes to effectively supercharge the = engine.=20 The rotary is similar except for the fact that the port is never = "closed" so the convergent reflective wave will never arrive at the = right time. It will either impede flow from the exhausting chamber or it = will "stuff" exhaust back into the intake side. The combination of = overlap and the fact that the port is open to two different chambers = when you could use a positive pressure wave, makes it impossible to use = typical two stroke tuning techniques. Likewise it is impossible to use "interference working" as is typical on = a four cycle recip engine. This uses one branch of the header as an = organ pipe resonator when the other exhaust valve is closed. You can = only design a system for a rotary that operates on the "independence = working" principle.=20 The literature (I have a graph from the pope's newsletter that he = bogarted from a Mazda technical paper and "copyrighted") and racing = practice shows a primary length of around 31in to give the best results = in the 5-6Krpm range. That is a long pipe to fit under a cowl. These = results were obtained with a single rotor engine. From the previous = discussion it should be evident that positive reflections cannot be used = with the rotary. Only negative or suction waves will help. With a two = rotor feeding into a collector and then into a divergent cone, the = effective tuned primary length is half of the single rotor. This is = somewhere around 15.5 inches. The cone should then be another 15.5 = inches long. Each rotor now sees the 31 inch tuned length plus an extra = suction wave from the other rotor. This of course assumes no positive = pressure waves go back up the collector (use as shallow an angle as = possible). Alternately the cone could be 24 inches long (available from = racing beat) and the header primaries could be 7 inches long. I don't = suppose anybody has ever tried anti reversion headers? The muffler is a another issue, better quit while I'm ahead (I think) Monty ------=_NextPart_000_0023_01C6034C.8A333F50 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Well,
 
I have nothing better to do on a = Saturday night so=20 I will subject you all collectively to my random thoughts (assuming you = read=20 this)
 
I have been trying figure out how to = cram a=20 muffled, tuned, road-race, exhaust system under my (tight) cowl. No = easy=20 task.
 
I am going to be running a Pport NA = high=20 compression motor.
 
The prevailing wisdom is to use 10-26 = inch primary=20 pipe into a collector to a 24 in megaphone that goes from around 2 in to = 4 in=20 dia. over it's length.
 
After looking at this thing for so long = my head=20 hurts I have concluded that the rotary shares aspects of a two cycle and = four=20 cycle but is nothing like either in terms of exhaust system = tuning.
 
Two cycle recips can use a = divergent/convergent=20 cone type expansion chamber. The timing of the pulses alternately draws = gases=20 out of the combustion chamber to assist scavenging to the point of=20 overscavenging at the operating point, and then "stuffs" the = overscavenged=20 mixture back in at the last moment as the port closes to = effectively=20 supercharge the engine.
 
The rotary is similar except for the = fact that the=20 port is never "closed" so the convergent reflective wave will never = arrive at=20 the right time. It will either impede flow from the exhausting chamber = or it=20 will "stuff" exhaust back into the intake side. The combination of = overlap and=20 the fact that the port is open to two different chambers when you could = use a=20 positive pressure wave, makes it impossible to use typical two stroke = tuning=20 techniques.
 
Likewise it is impossible to use = "interference=20 working" as is typical on a four cycle recip engine. This uses one = branch=20 of the header as an organ pipe resonator when the other exhaust valve is = closed.=20 You can only design a system for a rotary that operates on the=20 "independence working" principle.
 
The literature (I have a = graph from the pope's=20 newsletter that he bogarted from a Mazda technical paper and=20 "copyrighted") and racing practice shows a primary length of around = 31in  to give the best results in the 5-6Krpm range. That is a long = pipe to=20 fit under a cowl. These results were obtained with a single rotor = engine. From=20 the previous discussion it should be evident that positive reflections = cannot be=20 used with the rotary. Only negative or suction waves will help. With a = two rotor=20 feeding into a collector and then into a divergent cone, = the effective=20 tuned primary length is half of the single rotor. This is = somewhere=20 around 15.5 inches. The cone should then be another 15.5 inches = long. Each=20 rotor now sees the 31 inch tuned length plus an extra suction wave from = the=20 other rotor. This of course assumes no positive pressure waves go back = up the=20 collector (use as shallow an angle as possible). Alternately the cone = could be=20 24 inches long (available from racing beat) and the header primaries = could be 7=20 inches long. I don't suppose anybody has ever tried anti reversion=20 headers?
 
The muffler is a another issue, better = quit while=20 I'm ahead (I think)
 
Monty
 
 
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