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 7.1
I'm not too confident in those measurements so if anyone can confirm or point out any mistakes I'd appreciate it
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=shared
Fabrication 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
@SpookDog I can tig weld but I use scratch start since I don't have a real tig welder, this one works fine with steel, it's just harder without fancy controls. I'm not really good with stainless and it's more expensive, my friend works in a nearby factory where they only laser cut mild steel.
Cones aren't a bad idea, there's a software called cone layout, it might be worth trying
Replace it, your wheel can come out of alignment and the bike will jerk a lot when you ride
Mine's the same, runs about 1/4 of the gauge at max with no issues. You should avoid revving too high while the needle is still in the thin green line but don't let it idle for too long, it's generally a bad idea for 2 strokes. Depending on your mixture, the engine is warmed up when you see significantly less smoke coming out of the exhaust, trying to slam high RPMs in lower gears when it's cold will create misfires and janky throttle response.
