Resonator build thread
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Here I will list all useful resources I've found so far regarding the design and fabrication of a tuned pipe for a DT125R (and it applies for other 2 stroke motorcycles as well)
I am not an experienced fabricator nor do I have a lot of experience with 2T tuning so anybody with more knowledge should feel free to comment and correct me if needed.Free calculator (2T exhaust calc) http://birdcagesoft.com
The guy who wrote this software also made a series of videos on how to acquire needed measurements and use his program https://youtube.com/playlist?list=PLIxC_wjJqk0rYVOG6EpLU2EaAVWZ2saWA&feature=shared
Cone layout software (it's a free demo but you can use it even after the trial): https://www.conelayout.com/
Simple spreadsheet, likely not very accurate: https://docs.google.com/spreadsheets/d/1nksxtd8M9KeJJ8l10ZHtq8yk8W6gZQZhXmFXj4fGZC4/htmlview
Video of a guy using the above mentioned to fabricate an expansion chamber for a DT360 using the pie cut method: https://youtu.be/TgoHIF2boPE?feature=shared
Jambros' calculator topic on another forum, this spreadsheet is much more detailed and useful to someone who knows how to use it: https://www.rzrd500.com/phpBB3/viewtopic.php?t=16273
Another video where someone fabricates a resonator for an older dirt bike using cone layout and a wire to determine the path which the curves go along (it's in Finnish and there are multiple videos on this topic from his channel):
https://youtu.be/Q8k5hFfUA_o?feature=sharedFabrication of a scooter exhaust using the hydroforming method: https://youtu.be/DVeoDNHGEc8?feature=shared
Older post about hydroforming of 3D curved exhausts https://web.archive.org/web/20200221121820/http://www.eurospares.com/frame8.htm
Making shapes for sheet metal cutting is most accurate using CAD software and exporting them in DXF format, I know how to use Solidworks in case anybody needs help.
Generally, sheet metal thickness of cca. 1mm is adequate and regular mild steel is cheaper and easier to work with as opposed to stainless, rust can be prevented with temperature resistant paint and burning in the inside with oil.
Tig or oxy fuel welding is the preferred method since we can make autogenous welds with minimal heat input; Dedicated tig welding machines are expensive but a cheap inverter welder can be easily converted to a scratch start tig; https://youtu.be/aGDHX5JdOos?feature=shared
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From what I've gathered and managed to measure regarding my 1991 DT125R with 3ME00 stock cylinder;
Port timing: 174°
Port diameter: 34.5mm
Port length: 45mm
Flange diameter: 32mm
The temperature should be around 450°C making the BMEP right around 7.1I'm not too confident in those measurements so if anyone can confirm or point out any mistakes I'd appreciate it
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I think 174 sounds very low. I have measured 190-200 on 125 & 170 Athena cylinders, depending on base gaskets etc. From memory my standard 3MB cylinder is similar in exhaust port height.
Exhaust temp is medium temp in the pipe I guess? Measured close to the exhaust port (but not too close) I bet it will be over 600.
I think you could make a pretty peaky pipe (large diameter, and relatively steep cone angles) to gain power witout losing to much of the power band since it has the exhaust valve. However, I think you need to be able to tune the exhaust valve (Zeeltronic) to the new pipe, especially if it deviates significantly from the original pipe. Maybe take a look at the TZR exhaust dimensions for inspiration? -
I think 174 sounds very low. I have measured 190-200 on 125 & 170 Athena cylinders, depending on base gaskets etc. From memory my standard 3MB cylinder is similar in exhaust port height.
Exhaust temp is medium temp in the pipe I guess? Measured close to the exhaust port (but not too close) I bet it will be over 600.
I think you could make a pretty peaky pipe (large diameter, and relatively steep cone angles) to gain power witout losing to much of the power band since it has the exhaust valve. However, I think you need to be able to tune the exhaust valve (Zeeltronic) to the new pipe, especially if it deviates significantly from the original pipe. Maybe take a look at the TZR exhaust dimensions for inspiration?@Rallyfinnen I think you might be right about the timing angle, one of my repeated measurements came out as cca 185°. I could have used the wrong technique when measuring; Shined a flashlight through spark plug hole and basically measured between the times I can see any light coming through, used the magnet rotor to set marks. A solid, definite number would be useful; my machine has a 3MB00 cylinder and a standard thin gasket, it is not marked with "P" and has never been bored or ported.
As for the temperature, I didn't get reliable numbers with a multimeter probe at the flange with the exhaust off, so I opted for calculating it via BMEP which turned out right around 7.10
The temperature would be lower at the middle of the pipe and even lower at the convergent cone, the highest temp is supposed to be right at the exit of the cylinder and if I'm not wrong, that's the part that creates the pressure wave.