The Hodaka Club Forum

Maxie, could you illuminate the effects attributed to number and acuity of pipe bends before you get to the muffler (in your example) or the divergent cone in an expansion chamber. Thank you. Also, what was the final tune-ability of that epic header you were working with.

Hey Matt. All started with Harry Taylor's "how to build a trials bike" or something like that. Long header pipe recommended. I decided to lengthen with a curly header pipe and went from there. I tried routing this through a 93A Wombat pipe body. Heavy, no low-end. Set it aside for a long while, too many projects. Cool bike, might just put a Rat pipe or such on it. Always in limbo with my interest waning. New path required. Just jostling ideas. Maxie

Can't go wrong with that for your source material. Any time you'd like, just slide on a stock pipe, tune the carb and - presto - cool ride. I like that. Heck, you could even find a cool after market performance pipe and mod it to fit. Groovie.

Did you ever report just how epically long that header pipe is? (Somewhat longer than Harry suggested in the trials tuning sheet mayhaps?)

Note that a LOT of trials tuners have come up with header pipes around 20" long . . . but a LOT of those headers connected to a Sammy Miller silencer/muffler with a core tube virtually the same diameter as the head pipe. So, while one might consider the muffler core tube to be an extension of the head pipe, it was often a "given" in the testing which was done. (Over on Facebook you asked about this topic.) To me there were two things worthy of additional exploration/quandry in the photo which accompanied your inquiry. 1) Just how looooonnnnng is that custom head pipe you've got? (not counting the silencer it attaches to, since that is a "given" in many other previous projects) and 2) Would you expound on the topic of installing a second silencer/muffler after the one attached to the head pipe?
Ed

Eternal project. Back to here with the muffler idea sawed off and scrapped. Trials plumbing, all a vague mystery that I’m trying decipher from pictures and opinions. All seem to have a long header pipe. Did that, about 22 inches. Many trial type bikes use this Bultaco muffler. Bought one. Almost all trial machines have a terminal silencer way down the line, they must be too loud without one. This HT pipe silencer could be used and about the only place that I see this fitting properly. This mock-up is just hanging on the bike for position testing. Considerable job coming up should I make this a final assembly. Why am I getting skeptical here? Because I have no firm theory or dimensions of what is required to make this all work. Expansion chamber exhausts to be bought, stock pipes to use but I’m still at “Day One” in my quest to build a known and efficient trials exhaust system. Time to put this project back on the Think About It shelf while I finish three other fun projects maybe to return with enough information OR bolt some cool stuff from around the shop on blast some trails. All thoughts on going slow. Hodakas always seemed to want to go faster. Thoughts for the day. Maxie

Maxie, with any luck there will be a diagram with this post which will provide some food for thought regarding your exhaust tribulations. Hopefully the diagram will be an aid in your musings.

As mentioned earlier, most Hodie Trials exhausts have a long header connecting to an old Bultaco Sherpa T style muffler or a modern "off-the-shelf" accessory spark arrestor/silencer which is about the same size. So it would be reasonable to muse that the interior core of the silencer is just more head pipe . . . (hmmmmm). But one should keep in mind that the general layout has been independently "invented", "re-invented" and tweaked by multiple builders . . . and is known to work to provide good "low end" grunt. Your custom header is reported to be about 22" long with a unique winding path. I don't think the winding path introduces major issues, There are some very interesting modern trials head pipes which work just fine. You have previously mated the custom head pipe with a stock Hodaka exhaust and reported really disappointing "low end" performance. The diagram MAY show why. The stock Hodie pipe opens up into a comparatively HUGE interior volume (both diameter and length) compared to a "trials muffler". There's just no way it could perform the same as a typical trials system. It would be good to note that none of the "trials" exhaust systems I've ever ridden on a Hodie trials machine would be worth a dang on an enduro/"go fast" bike.

If you are NOT trying to achieve "TRIALS" power delivery . . . then mayhaps a "trials" length header is not the thing to start with. And if you are shooting for say, some sort of "middle-of-the-road", all-round, purty good, power band for a hunnert - then a head pipe like a toaster tank Super Rat or toaster tank Dirt Squirt might be a good place to start.

I previously asked about two full size mufflers in your mock-up. Actually, I "get" and agree with the concept. My own Bullfrog trialer has small outlet out of a single muffler and has quite a "bark". Lots of civilized older (and modern) trialers have a 2nd muffler. But there is usually a smallish "stinger" connecting the 1st muffler to the 2nd one - and then a smallish "stinger" exiting the 2nd muffler. (Again, this set-up is for "trials" power.)

. . . some thoughts for musing upon.

Ed

Excellent 'captain. I couldn't trust my recollection of wave mechanics from my college physics class a zillion years ago. So if the pipe is a consistent diameter curves and bends don't matter, yes? Hey, great discussion. Thanks guys.

Good and simple presentation Ed. Thanks! I can vouch for the original design not working and it is no longer with us. Looks like I'm on the right track with my 22" header and this 9 1/2 ish Bultaco muffler with its 7/8' ish exit. I think I''ll proceed at this point and see what this brings in performance and noise. Addition of secondary muffler can be an option. Got a good mount here, I''ll cut this flare off and proceed. Maxie