February 21, 20188 yr 11 hours ago, pschrauber said: I don't think the Banana style exhaust is better then the clubfoot style and to me there are two reason. The first is very obvious the clubfoot offers better sound reduction so is quiter. The second is obvious too, the clubfoot offers more througput or flow rate as the diameter of the two tubes are bigger then the one at the banana type. Second the Clubfoot offers more general back pressure in the exhaust system through the mace of voids, tubes and "windows" which allows a mild rear loading effect to the charge of air gasoline mixture which was pushed out of the cylinder. The Banana style exhaust was an interims solution and invented after the tobacco pouch style rear muffler which did not show any good effect. im not sure back pressure so far from cylinder actually does anything? And on bultos we always lengthened first pipe till the factory did it too?
February 21, 20188 yr 25 minutes ago, nigel dabster said: im not sure back pressure so far from cylinder actually does anything? And on bultos we always lengthened first pipe till the factory did it too? Which models of Bultaco Sherpa were fitted with a longer front pipe ?
February 21, 20188 yr Author Thanks all for your feedback, I've read enough to decide I will try a 'banana' for myself, it's been ordered and should arrive in about a week. I won't actually have the bike re-assembled and ride able for about another 6-8 weeks as other parts are elsewhere being re-furbed, such as the motor.
February 21, 20188 yr You might have to modify the inlet tube of the banana as they were made for the earlier engines with smaller diameter connecting pipes. It might be too small to mate properly with the 183 middle box outlet. Banana definitely noisier
February 21, 20188 yr Woody is right they need a short length of pipe welded to the inlet about 11/8 od x 11/4 ish long They are louder but I think a much nicer sound the reproduction ones seem a bit louder than the original bananas I have a reproduction one on my 183 and a cleaned and repacked original on a 125.
February 21, 20188 yr Wouldn't surprise me if the repro banana has nothing inside it.... I've just taken the banana off my 92 and replaced with a repacked but still with baffles clubfoot. Haven't tried it yet though
February 22, 20188 yr On 21.02.2018 at 10:38 AM, nigel dabster said: im not sure back pressure so far from cylinder actually does anything? And on bultos we always lengthened first pipe till the factory did it too? The different design layouts where dicussed in German Trialsport Magazine (GTM) by Felix Krahnstöver, but you can read all about a following article in GTM # 107 page 50 ffp. from February 1985 in an article written by Dr. Klaus Simon who was at that time a trials rider and engine engineer at Sachs, in the article he discussed the different possibilities / set ups für rear exhausts from one chamber absorber- to one chamber refection and to the combination of both and where where where the advatages and disadvantages and very important how to construct them*. The article recieved special attention by the readers so he wrote two additional about trials exhausts for Twinshocks and Monos: In GTM # 128 page 86 ffp. about the outtake or missing pipe and the mid section of trials machines and how to construct them*, In GTM # 205 page 58 ffp. about the loading effects of two stroke pipes in trials machines and about their deimensions*. * giving rules of thump and ranges to what ever you want to archive. To two stroke engines with the technology of twinshocks and air cooled monos these principles are still valid today, you apply them perfect to most new aftermarket exhausts, if you would take port steering or other more advanceed motor control unit too in consideration there would be a design change of the given numbers in need. To back pressure, it is a fact that a standard two stroke engine needs a bit of support depending air mixture flush from the exhaust side to work well, you can't change physics.
February 25, 20188 yr I have both at home and have tried both. For me apart from the banana looking a bit neater and being a bit lighter the clubfoot performs significantly better in all respects. The engine has a wider spread of power and more torque off the bottom with the clubfoot.The banana is noisy anyway and reminds me of the drop off in performance I get when my gassers exhaust needs repacking. Cheers Greg
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