All 2st School me on expansion chambers

[little squirt]

so is that trials bikes have no expansion chamber because they dont need the power curve of "being on the pipe" and having no expansion chamber means just a nice smooth flat power curve with no big "hit" meaning more controllable in tight short riding areas?

 

[Troy F Collins]

Everything you wanted to know but were afraid to ask

cool stuff

http://en.wikipedia.org/wiki/Expansion_chamber

unfortunately it doesnt show the rebound effect of the shock wave after it hits the piston covering the exhaust port and how it scavenges the top end with fresh mixture when the port is uncovered.....but you get the idea

 

[ohmygewd]

2t Expansion chambers are part of that black art of two stroke tuning...all l know is that a handcraft expansion chamber looks uber-trick!!

 

[Dirtdame]

Actually Beta has a chamber on it's two stroke model trials machines.

 

[little squirt]

thanks for the link, yea my general knowledge was:

1. Trials bikes = no expansion chamber, slow riding, tight situations

2. Dirtbikes = medium size chambers, slow or fast riding but alot of on and off throttle action

3. Streetbikes = large, long expansion chambers, fast alot of on the throttle wide open racing on paved courses....like the old kz's, rd's, and tz's

 

[Troy F Collins]

Of course the variable exhaust port serves to optimize things better even more.....the idea is the pipe needs to be timed for acoustic shockwaves relative to the required RPM........so Squirt I think your assesment is correct with the pipe lengths

In GP circles Honda's NSR's took thngs further...a small ECU, pump and reservor ,crank driven... injected various amounts of water into the expansion chamber for desired acoustic effects.....the system even had a tiny radiator tucked in by the triple clamps

then one day they called it Moto GP took the 2T's away

 

[CelticDude]

Walter Kaaden (1 September 1919 – 3 March 1996) was a German engineer who improved the performance of two-stroke engines by understanding the role of resonance waves in the exhaust system. Working for the MZ Motorrad- und Zweiradwerk part of the Industrieverband Fahrzeugbau (IFA), he laid the foundations of the modern two-stroke engine. His understanding of gas flow and resonance enabled him to make the first engine to achieve 200BHP/litre with his 1961 125cc racer[1]. His motorcycle engines were ridden to 13 Grand Prix victories and a further 105 podium finishes between 1955 and 1976[2].
Walter Kaaden was born in Pobershau, Saxony, Germany. His father worked as chauffeur to the sales manager at the DKW factory. At eight years old he attended the opening of the Nürburgring racing circuit, a formative event to which he later attributed his enthusiasm for engineering[2].
Kaaden studied at the Technical Academy in Chemnitz. He then worked at the Henschel aircraft factory at Berlin-Schoenefeld under Professor Herbert Wagner who invented the HS 293 radio-guided rocket-propelled missile. During the Second World War, he worked under Werner von Braun in the German rocket program.[3] At the end of the war he was interned by the Americans before eventually returning to Zschopau.
In 1953, the IFA asked Kaaden to take over the management of the racing department from Kurt Kampf when the IFA 125cc racers were being outclassed by Bernhard Petruschke riding the private ZPH (Zimmermann-Petruschke-Henkel) machine.
Engineer Daniel Zimmermann (born 1902) based his ZPH engine on the pre-war DKW which he heavily modified by adding a disc valve that allowed asymmetric port timing with a longer duration inlet phase. Zimmermann also used a new crankshaft providing 'square' bore and stroke dimensions (54mm x 54mm) that used stuffing rings to boost the primary compression ratio. However, the East German government didn't like the competition between the two East Germans and persuaded Zimmermann to reveal his engine's secrets to Kaaden. The result was the 1953 IFA racer.
Working with extremely limited resources, Kaaden began to develop the expansion chambers invented by Erich Wolf (the DKW designer) that had first appeared on his 1951 DKW racers. In 1952 Kurt Kampf copied this DKW innovation and fitted them on the IFA racers [4]. Kaaden used an oscilloscope to examine the resonance in the exhaust system and devised profiles to maximise the engine's efficiency. The net result of this development programme was that by 1954, Kaaden's two stroke 125cc racing engine was producing 13 bhp, more than 100 bhp/litre. This engine was further developed to produce 25 bhp at 10,800rev/min[5].

 

[CelticDude]

When I was in high school in Montana back in the 1960s, there was a group of us kids that used to go riding all the time. One of us got a copy of Gordon Jenning's book on expansion chambers. He was the editor of Cycle magazine for many years and an avid motorcyclist and racer. We took the book to our algebra teacher and he was happy to help us wade through the trigonometry and then we built a pipe for a Yamaha 80. The bike ripped and made a lot more noise doing it! Apparently Gordon published the book also in a set of articles in Cycle magazine in 1972 and it's a very good reference to anyone wanting to understand how they work. Plus it's a nice trip down memory lane with the ads in the side bar.

 

[Runner]

That is such a great article, thanks CelticDude!

How are modern chambers designed and analyzed? Does CFD (Computational Flow Dynamics) applications exist for chambers?