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yzf 1 · Post by **yzf 1** » Wed Jul 23, 2003 3:48 pm

Has anyone tried a 4-1 or 4-2-1 system using smaller or larger diameter tubing. The theory I've been told is smaller dia. tubing = more torque. Larger dia tube = more top end. My engine will not support an exup system - Any ideas? I've seen a simular idea in practice on a stock RF9what-ever where the first 6" of the header is of smaller dia. tube Im open to comments

flyingcircus68 · Post by **flyingcircus68** » Wed Jul 23, 2003 7:21 pm

Actually there are to phenomena occurring simultaneously. Mass flow (inertia) and acoustic wave. The analogy is a river flowing down stream with waves on its surface moving in not necessarily the same direction. The theory behind exhaust acoustics was dealt with in the sixties. A book titled "The scientific design of intake and exhaust systems" by Philip smith and John Morisson covers Pipe diameters, collectors, balance tubes and Mufflers. They developed an apparatus with a disk valve that allowed the pressure in the exhaust pipes to be measured at any point relative to the crank position. They showed how back pressure and pressure waves varied at the exhaust valve over various rpm. Back pressure would only rise around 1-2 psi with increase in rpm. Peak pressures from waves would amount to 6 - 8 psi. They showed how the dominant factor in exhaust system performance was the phasing of the wave peaks relative to the exhaust valve motion (the reason why cam timing is effective). They showed how peak volumetric efficiency occurs at the rpm where the negative pressure peak is in phase with the exhaust valve closing. They covered various schemes in controlling phasing such as stepped pipes, tapered pipes, 4-2-1 pipes etc. Stepped pipes are covered in an example of a self induction 2 stroke diesel engine. The 4-2-1 junctions are considered "interference" design. According to the book, the branch not flowing acts as a separate resonator, kind of like blowing on a jug. The combination of the wave from the "interference" pipe and the primary pipe wave result in completely different phasing than a primary pipe alone. It also recommends attaching lengths of capped pipe at strategic locations to introduce "interference" to change the phasing. They also showed an experiment in affecting phasing by restricting flow in the primary pipes (sounds kind of familiar, doesn't it) and that this was as affective as the "interference" method. I guess the engineers at Honda and Yamaha both read English and have studied the contents of this book for exhaust tuning

yzf 1 · Post by **yzf 1** » Sun Jul 27, 2003 4:15 am

Circus, Thanks for the reply. Its obviously not as simple as big/small = top end/torque etc. Its just as obvious I need to find myself a bookstore and get "educated" Once again, thanks for the help

LC130LOAD1 · Post by **LC130LOAD1** » Sun Jul 27, 2003 8:34 am

I have not commented on this - yet. Ask yourself this question: Don't you think that somewhere along the line that someone (name any pipe manufacturer) developed the "best pipe" for the R1? There is not going to be a magic breakthrough for pipe technology for the R1. Unless you have a mandrel and some good welding skills and a lot of time with a dyno there is no way you are going to develop a pipe that is going to outperform something you can buy off the shelf. It's all been done by someone else. I loaned the "real" Kerker my 83 GpZ1100 so they could develop a pipe for it. When I went to get my bike I was shown a pile of at least 20 pipes that had been tried and discarded. Kerker gave me two pipes to use, a 4-2-1 and a 4-1 pipe. The bike liked the 4-2-1 the best. When the Yamaha 5 valvers first came out (think FZ750, 750 Fazer, FZR1000) no one could make a pipe that really worked for those bikes. Even the stock pipes didn't work that well. Yamaha had to compromise the pipes in order to get the "smooth" powerband everyone wanted. When Yamaha stuck the EXUP valve on them eveyone was amazed at how well they worked. Like magic. It took people almost 5 years to figues out how to make a non-EXUP pipe work for the FZR1000/YZF750. Reverse taper headpipes, large diameter headpipes and small collector pipes, every combonation has been tried. That;s why I can't figure out what you want to do and why you want to do it, other than because you want to. Me? I would rather go riding rather than try to reinvent the wheel.

flyingcircus68 · Post by **flyingcircus68** » Sun Jul 27, 2003 1:49 pm

I agree with you there. I'd rather ride. I have played around with bikes due to curiosity and I have come to the realization that modifications are big black holes which suck up untold hours in search of the mythical combination. I have spent more time than I would like to admit to myself in something as simple as jetting to obtain the best compromise for all temp/situations. I recommend reading the book to satisfy curiousity only and not to reinvent the wheel.

EXUP Worldwide

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