Expansion chamber header pipe angle question

[Knuckledragger]

I want to know if the two 45 degree angle bends from the motor to the expansion pipe are to hard and are hurting my performance at all. Or is it better to hack and weld to get the straightest flow as possible. The way I welded it was to avoid hacking the RM85 pipe itself and it fits perfect the way it is right now. Just want some opinions it. Should I leave it as is because the bends are not that hard and pretty soft. Or hack the expansion chamber to get the straightest flow as possible. Check out the picture and the springs are temp. Until I get some real springs.

 

[Knuckledragger]

Another picture of the angles in the header pipe before the expansion chamber

 

[maniac57]

While I'm sure you are in fact reducing flow with this setup, I doubt you would notice any difference if you did it differently. Your setup should work just fine if it holds together.
The china dolls simply don't have the power for this to be a problem issue unless you get real silly laying out the pipe routing.

 

[Theon]

Using a very similar pipe I found it works well at stock length.
By cutting, rotating and rewelding, it will fit nicely with out extension.
http://motorbicycling.com/showthread.php?t=56138&page=3

 

[Knuckledragger]

When I had the 3, 45 degree copper 1 inch pipe connectors it had more power and sounded like a sick dirt bike . You could hear the expansion chamber And it was on the power band the whole time. It felt smoother when WOT and topped out. Now it shakes and vibrates when it's WOT topped out and slower now!!
I don't know what to make of it, it was way better with the copper than the steel pipe I welded.

 

[Venice Motor Bikes]

The header length is very important!!
That factory motorcycle pipe you're using is already about the right length for proper tuning.
You'd really be better off cutting it and turning it to fit around the frame (& get the factory flange as close as possible to the engine exhaust port).

 

[Venice Motor Bikes]

Here's some pics of one I recently did using a FMF CR-80 pipe.
If you look close, you'll see that I cut off a couple of inches of the factory pipe & then made my own flange to bolt onto the engine; (keeping the pipes original length).

 

[TomSimon]

Back when I was racing 100cc Karts, it was pretty common knowledge (and worked in practice) to change the expansion chamber's straight section length, to tune the engine for peak power at optimum rpm range, for a given track, altitude, and to a lesser extent, weather conditions.

If fact, all the fast guys carried various lengths of straight section in our spare parts boxes for use on race day. I found that a certain pipe (expansion chamber) would have an effective rpm range in which it gave that particular engine a boost. The rpm range in which it worked, or boosted, was pretty constant. It's been 20 years, but I remember that range being about 3,000 - 4,000 rpm on the 100cc 2-stroke Yamaha engines I used.

That length between the piston and beginning of the first expansion cone made all the difference in the world. The difference was not peak power, rather, when peak power happened withing the rpm range. We used centrifugal clutches, and you needed to adjust the rpm engagement of the clutch to work in concert with the pipe's rpm range... it was a lot of trial and error, tuning, note taking, stopwatch anf lap times, and 'seat-of-the-pants' engineering.

All things being equal, if you increased the length of the straight header section, it had the effect of lowering the place in the rpm range where the expansion chamber would 'kick in'. To compliment this effect, you would tighten up the clutch springs, lowering the clutch engagement rpm as well. Conversely, if you shortened the straight section, the 'pipe' kicked in at a higher rpm.

I appreciate having to add pipe to make it fit, but know that by doing so, you are changing the engine's 'optimum rpm power range'. You could make it so long, that it would kick in at 16,000rpm, an rpm your engine may never reach.

I'm not expert on the subject of exhaust tuning, just a student, trying to pass on a little experience... good luck