PE250B Vintage Supermotard

[James P]

This isn't quite finished, but there isn't much left to do.

It isn't an 'off-road' bike any more, so may not be to everyone's taste!




More photos and info here: http://diffrentstrokers.com/phpBB2/viewtopic.php?t=2511


Regards,
James

[LWC82PE]

Great work. Would be a good thread for here http://suzukipemotorcycles.proboards.com/

[James P]

Thanks Leith. Is that 'proboards' forum new? I wasn't aware of it until now.

Regards,
James

[LWC82PE]

Yes new in November. Replaces the Yahoo site which is no longer.

[Hoony]

interesting, can you explain the concept of the pipe and if you noticed the diference in power delivery ?

Regards,
James

[pokey]

Interesting pipe. Tis my understanding that the stinger or bleed can be positioned anywhere  on the midsection with no noted difference in performance. Ive seen a few on scooters. is an okay youtube video that explains it not bad. https://www.youtube.com/watch?v=n5AvG-hDvY8

[80-85 husky]

did you end the pipe cone to a point?

[James P]

interesting, can you explain the concept of the pipe and if you noticed the diference in power delivery ?

There is a brief description of the concept in the Diffrent Strokers write-up (http://diffrentstrokers.com/phpBB2/viewtopic.php?t=2511). Since modifying the exhaust, I have only ridden the PE around a concrete car park for about 15 minutes. It felt pretty much as I remember from a 'response' point of view, but I'll have to wait until it is officially 'back on the road' for a proper evaluation. In theory, there should be no difference in performance compared to the previous set-up. However, dyno runs before and after would be the only way to be sure if the theory is good in practice.
The first (and only previous) time I tried out the 'side-bleed' stinger concept on another project bike did not provide any info on performance difference - I made that first exhaust up from a pair of pressings and fabricated the header pipe and stinger from standard bends - I didn't have any previous experience of that particular pipe in the form for which it was originally designed. Having said that, the characteristics of the finished product were very agreeable...not valid for a comparison though.

did you end the pipe cone to a point?

No - I just blocked it at the end of the reverse cone (i.e. at the start of the existing stinger) with a plug, which also served as a sleeve for joining the original stinger/tailpipe back together. I did it the same way on my only previous side-bleed attempt. I'm not sure if this is the 'correct' approach, but I couldn't think of a better way to do it which would satisfy both technical and practical considerations. With the standard stinger arrangement the 'true' end of the reverse cone is an imaginary point...and trying to manufacture a small cone extension/plug/sleeve would have been a bit fiddly. I don't recall seeing the reverse cone of any expansion chamber end in a closed-off sharp point, although I'm not claiming this as technical justification of my method! If anyone has any input on this particular aspect, please let me/us know!


Regards,
James

[James P]

...is an okay youtube video that explains it not bad. https://www.youtube.com/watch?v=n5AvG-hDvY8

I thought I should have another look at that video (I'm pretty sure I saw it while researching the internal stinger concept previously). I don't necessarily disagree with anything the narrator says, but stingers arranged as per the second or third drawings will lead to lower performance if Gordon Jennings' findings are to be accepted (and if I have understood them correctly ) - he found that stinger exits which start anywhere in the reverse cone caused a drop in performance compared to the standard set-up (the first drawing in the video). Jennings stated that an internal stinger should start about an inch ahead of the reverse cone, which I take to mean 'in the parallel-wall belly section'. In the absence of contradictory evidence, I have assumed that an outlet anywhere within the boundaries of the parallel-wall belly section will perform in similar fashion (i.e. same performance characteristics as standard set-up, but with less noise).

Two-stroke pipes are a minefield and I have so far avoided designing my own in preference to buying (or sometimes building and/or modifying in accordance with) known/proven designs. I just don't have the time to experiment by continually chopping and changing pipes...only to end up with something which may be the same as (or more likely inferior to) an existing product.

However, all of this does not mean that I'm not interested in the design aspects...but I know enough about them to realise that I don't know enough about them!

Regards,
James

[Hoony]

Since modifying the exhaust, I have only ridden the PE around a concrete car park for about 15 minutes. It felt pretty much as I remember from a 'response' point of view, but I'll have to wait until it is officially 'back on the road' for a proper evaluation. In theory, there should be no difference in performance compared to the previous set-up..............

Why did you do it then ?

[Momus]

It's a good experiment that PE and opens up a few packaging possibilities for, say, the long down pipes on big bores where the muffler is vulnerable.

A friend had a YZ80 with a snail pipe back when, with the similar exit position. The bike went ok but the issues with noise, dust flying up from the ground and mess from the smoke and splooge were there as well.

[80-85 husky]

the whole point of the centre bleed is to have a complete pointy cone end to the pipe which sends a complete reverse wave back to the exhaust port therefore giving better performance by holding more charge in the cyl instead of loosing a tad through the stinger hole in the wave. a block should have some effect i guess but who knows. a dyno before and after is the only real answer and its probably a gnats difference anyway..looks way cool!

[James P]

Why did you do it then ?

Sorry, maybe I didn't make it very clear. The prime objective for modifying the exhaust was to reduce the noise. If the performance remains unchanged, I'll consider it a bonus!

the whole point of the centre bleed is to have a complete pointy cone end to the pipe which sends a complete reverse wave back to the exhaust port therefore giving better performance by holding more charge in the cyl instead of loosing a tad through the stinger hole in the wave. a block should have some effect i guess but who knows. a dyno before and after is the only real answer and its probably a gnats difference anyway..looks way cool!

Thanks . I can't argue with the theory, but am hoping (as you suggest) that the short length missing from the reverse cone will make little difference to the performance compared to the previous set-up, where the cone was also 'incomplete'. The reverse cone is still the same length as before and it remains to be seen whether my 'seat-of-the-pants dyno' will detect any difference - hopefully not!


Regards,
James

[pokey]

That small disruption to the waves at the end of the pipe I too doubt would be measurable considering the  return waves would not be perfect as the pipe isnt straight so it has to bounce off the walls that are rarely parallel and then we have the Hockey stick header. "IF" the entire pipe was straight and in a direct line to the port then maybe it could be worth while completing the end cone.

Being as the stinger is in the mid pipe where it would not catch as many  sound waves it should,in theory, be a quieter system. I do like the idea to untangle the python of a header for big bores and maybe run the bleed to the other side and exit at the rear but on the opposite side to the chamber.It has me thinking.

[LWC82PE]