Average exhaust port diam, port length, and port flange diam on the china girl engine

[snip]

I was wondering if yall could give me some specs for your china girls including
port diameter
port length
port flange diameter
also looking for your port timings and if you have the time the average exhaust temperature your exhaust is at on a ride
why do I need all this? I'm making custom expansion chamber tuned pipes and need some specs to have a good formula for a "universal" exhaust
thanks

Edit: if you could give me your stroke lengths that would be appreciated

 

[Street Ryderz]

I was wondering if yall could give me some specs for your china girls including
port diameter
port length
port flange diameter
also looking for your port timings and if you have the time the average exhaust temperature your exhaust is at on a ride
why do I need all this? I'm making custom expansion chamber tuned pipes and need some specs to have a good formula for a "universal" exhaust
thanks

Edit: if you could give me your stroke lengths that would be appreciated

This will be quite the task, the china girls stock porting vary quite a bit, has two different strokes with different rod lengths used in both which alters timings.
Those whom do port work generally do their own thing making no two the same and having an effect on the over all length needed, then there is fitting it to different style frames.
Port length/depth is easy at 28mm (center) however the windows can vary greatly with the average being 23-24mm across and 11-12mm in height which gives an equivalent dia of 17.83mm - 19.03mm, big difference there and that's just stock as most prefer to widen everything when porting as well as change the timing, my ports are all matched at 23mm and that's not very aggressive compared to some as I prefer to retain torque as much as possible with improved flow/cylinder fill and keep rpm at or below 11k.
Port timing is critical in determining pipe length and stock timings can be between 140-150 depending on stroke and rod length and most tuners/builders prefer 170 or more with 20+ degrees of blow down when going for high rpm or if torque is the goal staying just under that with slightly less blow down, ether way it's a huge difference again.
Port flange dia can be anywhere from 19 -23mm depending on model, and that is stock untouched if ported ??? depends on the builder/tuners choice.
Exhaust temps also will vary greatly with so many factors contributing to it, I can tell you that an engine with good flowing characteristics and an average running temp of 220-240f will have around 1300f into the pipe for about the first 4" or so.
Stroke lengths are 38mm and 40mm but there are also 41-44mm stroker cranks that many use.

 

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thanks for the info!

here is what I have so far, I'll try and keep you updated as this project progresses

 

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What do yall think of these specs?

 

[Street Ryderz]

This is what IWT's pipe design for a stock China girl would look like, 2 stage pipe very short head tube and right into the divergent section, this aids pull from the cylinder and case for the next charge and this angle has alot to do with the velocity the exhaust gasses escape the cylinder and keep heat under control. Above you have a two stage pipe shown with long head tube before the divergent section this will slow the exhaust gasses escape, create heat in that section and diminish the aid/pull on the cylinder and case for the next charge, this also makes fitting the pipe much harder as this section will have to be curved to allow fitment to the bike. No pipe designer software takes into account the bends/curves needed for fitment unfortunately and this leads to a whole new set of things to consider.

 

[Street Ryderz]

What do yall think of these specs?
View attachment 103778

40mm at the flange is awful big, and in the first section will really reduce velocity. The largest I've ever been able to fit and still be able to bolt it on is 32mm and that was a b**ch as it leaves no room for the nuts to clear without dimpling the tube, even with cap head bolts rather than the studs and nuts was very tight. The stud holes are 40mm center to center.

 

[snip]

I see
what do you think about a 20mm flange? also thanks for the info and references man

 

[Street Ryderz]

I see
what do you think about a 20mm flange? also thanks for the info and references man

23-30 is pretty safe.

 

[snip2]

ok, here are my two designs that I like the most before I figure out curves so it fits the frame and all that

 

[Street Ryderz]

ok, here are my two designs that I like the most before I figure out curves so it fits the frame and all that
View attachment 103779 View attachment 103781

The second one looks pretty good, I've tried one like this and found that a larger belly section at 100mm dia works even better and the steeper angle of baffle cone (convergent section) had a stronger hit though a bit narrower band width.