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Discussion Starter · #1 ·
Hi,

I need the experts here to help me with an exhaust question.

On my Scrambler 2007 I would like to change the pipes to one each side, bandaged.

Is a straight-through exhaust the same as a free flowing exhaust?

My plan is to soon upgrade the motor to a 904cc Wiseco, Airbox cleanup etc, so free flowing pipes make sense, but I am not sure if they are one and the same thing. I can get my local custom builder to make me some straight through pipes, but perhaps I am missing the point.

cheers

Peter
 

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Specialty Spares has these M3 pipes that are high - and one for each side - that sort of go with the Scrambler style. Check 'em out.
 

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Discussion Starter · #3 ·
Thanks David,

That is the sort of style I am looking for, but the photos aren't clear enough.

However I would still like to have some fabricated to my own design, is why I need to know whether 'free flow' = 'straight through'.

If not is it possible to fabricate free flowing myself (together with the custom shop)

cheers

Peter
 

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These bikes are very picky on what pipes make hp. The high pipes out there dont seam to make the hp because they all have a sharp bend where the pipe comes out of the head.There is alot of testing that goes into makeing pipes that work on these bikes I dont think you want to get into making your own.I wouldnt go with the 904cc Wiseco kit the tpusa kit is alot better .You wont make the hp with the 904cc Wiseco kit you can with the tpusa kit.The 904cc Wiseco is 10.5to1 comp. ratio the tpusa is 11.5 to1 .I had a 989 wiseco stroker kit it uses the same sleeves as the 904 kit .Ihad nothing but trouble with the sleeves moveing and leaking.I am running a tpusa 904 kit now it hasnt leaked or used a drop of oil in the first 1000 miles.It sealed up right off the oil looks like new when you change it .Wiseco kit never sealed up like that.time you buy the 904cc Wiseco kit and pay someone to put the sleeves in it wont cost you much less then the tpusa kit.
 

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Is a straight-through exhaust the same as a free flowing exhaust?
They are the same. You can look through from one end to the other on a straight through silencer, on a more baffled silencer you can't see through due to the baffles. A straight though silencer is generally louder and more free flowing than a baffled silencer.

A bike with just the down pipes/headers like the old Triumph TT can also be described as a straight through exhaust. But just the headers don't work well on our bikes, not only are they very loud but you lose power at both the top and bottom end and gain very little in the mid range. But if you don't like your neighbours, they're the best.
 

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Discussion Starter · #6 ·
Pieman,

I had been speaking to Bob Farnham about increasing the power of my Scrambler and he said lose the Tors, not great for power, better to go with something like the Zard.

Question: Is it the length of a straight-through that determines the power/torque curve? With a 2 stroke it is easy to find calculations for the ideal length, but I have not heard this being discussed in relation to 4 strokes. There must be something else that dictates the ideal hp/torque.

Peter
 

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Peter, it is generally down to the length of the headers combined with the length of free flowing silencers that dictate how the system is going to effect power and where in the rev range it is made. A system with headers say 12" shorter than our standard pipes will generally make power higher up the rev range, where as a system with headers 12" longer than our standard pipes will generally produce a power peak lower down in the rev range.

I have used "generally" a lot in the above example because making a good exhaust system for a particular bike is not as simplistic as I have stated. Many other factors come in to play that can raise, lower, broaden and narrow the power band.

For the price of the Zard and Arrow exhausts, you can have custom pipes made that would be just as good, if not better.
 

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As mentioned,straight thru and free flowing are the same. But you can still have muffled pipes and still be free flowing/straight thru,ala,Predators. Your custom made pipes can have terrific performance over stock or equal [or less] performance,but better sound.They WILL sound better with some sort of lining or baffling inside. The issue with twin high pipes with no little can or megaphone on them,will be getting a good sound with the look you`re after with a 1-1/2" or 1-3/4" pipe diameter. Cramming one of those cheap beer can opener punched baffles in the pipes will not sound good or help with performance.If you can design a system with at least some sort of 2" section,that will allow you to get some good baffles in there and preserve your performance. But not a full 2" set of headers.There`s just TOO much flow then.A set of stepped pipes will work good and can give you a good boost down low,if the smaller diameter pipes are fairly long,before the "step up". Of course,a 2into1 would be best,but I`m biased that way:D I vote build your own and leave a little leeway for some changes before final finishing.
early twin pipes

current 2into1,and putting some bends in to keep the pipes tight,[and your legs burn free] will NOT hurt performance on a Bonnie.
 
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