The exhaust system is usually the first major item on any owners shopping list. Purely on aesthetics alone, shiny new expansion chambers rank as the number one upgrade! Just their presence is bound to invoke the "What else have you done to it mate?" and "How fast does it go now?" type questions from onlookers!

It is impractical to tune any aspect of the standard exhaust system, so a complete replacement system is required, or if your finances won't allow, at least a pair of less restrictive end cans. High quality end cans in the UK can be bought from Swarbrick Racing in either carbon fibre or alloy, priced at £127 and £66 a pair + shipping respectively.  Swarbrick Racing can be contacted on 01995 640291 and are in Lancashire.

Choosing the parts.

First decide on how much performance you require, if you are just looking for a modest increase in speed, a basic speed delimiter and a pair of end cans will be more than adequate. However, if you are trying to extract the last 1/1000% performance out of your bike you will want a system such as the titanium Ethos one below.

The benefit of a titanium system over the more common stainless steel (SS) systems is purely a weight saving. Unless you are out to build the ultimate 250cc "proddy" racer or have just won "Who wants to be a millionaire?" I don't think the cost can be justified as it is more than double that of the SS system.

The next available choice is design. Most manufacturers market a range of designs, each having a different power characteristic. One popular design is the NSR500 style where both chambers exit from under the Gull-Arm. Although looking highly attractive, this is the least efficient system due to the physical shape of the expansion chambers. The best design, performance wise, is any system following the stock layout.

Although each system can look very similar in design, each will require the jetting optimised to suit it, so in swapping pipes, say from Jha's 500V to their SP type or vice versa, don't be surprised if you don't immediately get the results you expected!

Fitting the system.

Most aftermarket systems now come with separate manifolds and spring clips to hold the various sections together. Bear this in mind if you are modifying your bike in steps, for example, if you intend to buy end cans only, with a view to fitting a system at a later date, check that the system you are buying can be used with your bolt on cans! Below is a diagram of a typical aftermarket manifold and its associated components.

When fitting the new manifolds always use new gaskets and remember that the rubber O-rings, if used, will need replacing every couple of months as they rapidly deteriorate with the heat generated by the engine and exhaust gases. Replacement O-rings can be bought from any good hydraulic hose specialist at a fraction of the cost rather than going to the exhaust manufacturer, check in the Yellow pages for a list of local suppliers. Pirtek in the UK supply excellent replacements for only a fraction of the cost of the OEM parts!

Benefits of spring clips holding the sections together are ease of assembly and disassembly, and that GP style look! The chambers are also easily removed for periodically checking the RC Valve adjustment. The down side is that the clips are notorious for "buzzing" when the motor is revved, and that they can quite often mysteriously disappear overnight!! 

Aftermarket motocross systems use spring clips to hold them on so a visit to your local MX shop will be the order of the day soon after you've acquired your new system. Apico make a very good cheaper alternative to the supplied springs (part# spring 90mm!) and as they are mild steel instead of stainless steel, can be both fitted (stretched) more easily and have their ends crimped to help prevent themselves working loose again. Since using these springs on my manifolds I have yet to loose one!

HRC systems come complete with rubber shields similar to that on the side stand (kickstand) spring to stop the aforementioned "buzzing", a good alternative is a length of heatshrink on each spring or simply a short length of electrical tape wound around them, although the heatshrink is definitely tidier and will last longer! Another good tip is to lockwire the sections together. This provides added security just in case those springs do work loose 100 miles away from home! (It also stops some bright spark running off with your end cans when you're not looking!)

One problem you may encounter with some systems is that they will not clear the original bodywork. As they are optimised for performance their design sometimes means that there just isn't sufficient room to squeeze the chambers into the required space! If you have opted for a full performance system rather than one that's simply more pleasing to the eye, this is something you'll just have to live with, but will probably only require the slightest of trimming.

Some expansion chambers,  the Ethos SP Over-rev's for example, require the radiator moving forward approximately 10mm (easily done by simply bending the lower mounting bracket or by fitting 2 longer studs into the barrel and adding two 10mm spacers) and the plastic radiator shroud trimming a little. The fairing lowers can also touch the chambers and thus may need a little trimming. A small 60mm x 25mm x3mm alloy plate can be fabricated to hold the two lower fairing sections together at the rear as the standard plate will  no longer fit with fatter pipes. A simple fix would be a couple of holes drilled in the underside and a couple of cable ties used to fix the 2 halves together!  For the performance gain, this small amount of work is well worth the effort!

 Original product images reproduced by kind permission of Jha and Ethos.