Exhaust Termination Box on a motorcycle?

[seattle smitty]

I spoke/wrote too soon. When I was into bikes, nothing on the street pulled rpm into five figures. I see why you were wondering about the t-box, Dave. I'll clam up and go away. But first, Brian, I bet you had a mile-wide grin when you came back from your first ride with your home-brewed pipes!!!

We've had a year without spring and not much sign of summer here, but it's bound to come, and I gotta put my ol' RD400C ring-dinger together again so I can go surging down the road.

[Pinhead]

Bringing this subject back into play, I've got some questions (I'll try not to completely hijack your thread).

First some background. I drive a 1979 CB650 (626cc) SOHC-4 motorcycle that needs some work on the exhaust; the pipes rusted all the way through just before the muffler and both mufflers rotted off. All I've got right now is the header primaries and the collectors (or more accurately, what's left of the collectors).

SOHC 4-cylinder
2 valve hemispherical heads, 9:1 CR
59hp @ 9000 rpm, 11.2 lb-ft @ 8000
9500 rpm red-line
4-2 "dual exhaust" system

Camshaft
-Intake
--Opens: 5° BTDC @ 1mm lift, 58° BTDC @ 0 lift
--Closes: 35° ATDC @ 1mm lift, 127° ATDC @ 0 lift
-Exhaust
--Opens: 40° BBDC @ 1mm lift, 121° BBDC @ 0 lift
--Closes: 5° ATDC @ 1mm lift, 65° ATDC @ 0 lift

My temporary solution was to simply clamp on a piece of 2" ID straight-pipe on the end of each collector. It runs much better with the 2" pipe than with half a collector (I'm assuming that my pipe is an extension of the collector) but I'm not satisfied with "tuning by chance." What other info do you need to design pipes with Pipemax? I don't want to custom-build the entire exhaust system if I don't have to... Is it possible to input the "stock" primary lengths into the software so it'll give you the collector diameter/length?

What this is leading to, is the mufflers (bringing this post back to the thread's subject). Once I get the correct collector length figured, I don't want to just throw a muffler on the end of it; without a termination box, all of that tuning would be thrown out the window.

I figured that a 4" ID pipe ~7" long would be plenty large enough to suffice. I would then use a 4" OD muffler on the end of that to make it look good.

I'd like to make it simpler to construct, however. What if I used a 3" ID glasspack about 24" long right on the end of the collector? The volume is definitely there at 2780 cc but would the glasspack itself actually act as the termination box, looking like "open air" to the collector?

The two criteria that I read about termination boxes, is that there has to be a "large change in CSA at the end of the collector" and it needs to be "8 to 10 times the volume of one cylinder per bank." The glasspack would meet both criteria in this situation.

But I have yet ANOTHER question (or series of questions). Refer to the attached picture.

Which one of the three figures is optimal? With my experience with speaker port tuning, I assume that the volume that the collector takes up inside of the termination box (last two figures) takes away from the volume of the termination box. In consequence, the last two termination boxes would have to be slightly longer or wider than the first one. This would be easy to overcome, however, when working on such a small engine. Any advice???

[Pinhead]

And would this work to find my optimal collector length?

Old tuning trick, install collectors too long, say 24". paint stripe the length of the collectors with bug bomb spray paint. Make cruising speed run.

Ok, the paint will burn to a point, that point is the limit of the reverse pulsation wave, how far air is being sucked back. Cut trim collectors 1" behind that point.

[1989GTA]

The 2nd or 3rd drawing would be best depending on the length of the collector your motor requires. Also I assume the exit will go straight into a muffler of the same diameter? You might be able to combine the two with some welding and fabrication. I don't think the paint idea will work in your situation.

Some ways to find the correct collector length would be track times, dyno results or buy a program like PipeMax to get you into the ballpark. One more thing the transition from the termination box to the muffler will be key. You might want to neck down the termination box into the muffler for a better transition.