Know Your....................................... Exhaust pipes. What they give you and why they give you it.
Exhausts are an easy way to milk that extra performance from your machine while making it sound and look bloody awesome in the process. For more info we caught up with Dave at SP Engineering to get the lowdown on pipes, systems and everything in between… FB: What is an exhaust?
DP: Basically, it’s a set of pipework designed to disperse combustion gas and heat away from the rider, while suppressing noise and helping the engine to perform with greater efficiency.
FB: How does it work?
DP: All combustion engines produce exhaust gases, which are collected from the cylinder head in the engine by an exhaust manifold. The exhaust manifold then acts as a funnel, diverting exhaust gases from all cylinders of the engine then releases them through a single opening – often referred to as the front pipe/ downpipe or header pipe... then through the silencer where most of the sound dampening occurs. So, on a four-stroke engine when the piston is heading down, the inlet valve opens, creating a vacuum which pulls air into the chamber. Fuel is then injected into the cylinder and is ignited to heat up the air in chamber – this creates a pressure which pushes the piston down. The exhaust valve will open as it rotates, allowing the fumes/gases to exit through the manifold and travel through the exhaust system. At this point the heat and gas will be silenced through the muffler as it travels through the exhaust system.
FB: What is a catalytic converter?
DP: A catalytic converter is a device that uses a catalyst to convert three harmful compounds in an exhaust into harmless compounds: hydrocarbons (or unburnt fuel), carbon monoxide (gas formed by the combustion of fuel) and nitrogen oxides (created when the heat in the engine forces nitrogen in the air to combine with oxygen). In a catalytic converter, the catalyst (in the form of platinum and palladium) is coated onto a ceramic honeycomb or ceramic beads that are housed in the exhaust system. The catalyst helps to convert carbon monoxide into carbon dioxide. It converts the hydrocarbons into carbon dioxide and water. It also converts the nitrogen oxides back into nitrogen and oxygen.
It tends to temper the sound you can get from an exhaust too, which is why many people look to remove the cat (often called a de-cat) to increase the noise volume! We have developed and are developing an ever-increasing range of decat exhaust systems for that exact reason – people want to be heard on the road because noisy pipes save lives… FB: Why are standard exhausts so chunky?
DP: Standard exhausts sometime house catalytic converters within the pipe, so tend to be large. Manufacturers also have to build an exhaust to reduce sound level to suit national or European standards. In order to gain this amount of sound reduction, a large canister is required which is made of a series of baffle plates.
FB: What material are exhausts usually made from?
DP: Exhausts used to be made of mild steel which often corroded and needed replacing or upgrading, whereas most modern exhausts are now made from stainless steel, or titanium for the higher range of models. While Titanium is lighter, stainless steel is somewhat more durable. So it’s well worth looking for an exhaust made from a high grade of stainless steel to ensure it stands the test of time. Here at SP Engineering, we use 304 grade stainless which we are happy to offer a lifetime guarantee on.
FB: What’s the main difference between an aftermarket can and a standard one?
DP: Aesthetically, the biggest difference between a standard OEM fit exhaust and aftermarket exhaust is size as well as the fact you have a wider choice of materials and shapes, which gives you the chance to make your bike more personalised to your style. As well as cosmetic enhancement, additional performance can be gained by using an open pipe or straight through system which increases the note and gives you much deeper sound. Generally, the smaller the aftermarket exhaust is, the louder it will be. By adding an aftermarket can, throttle response can also be improved with power gains also being found in the mid-range. Most aftermarket exhausts are also lighter so can offer significant weight saving.
FB: And then with a race can?
DP: A race can maximises performance and is usually a bit noisier due to having a larger
diameter which allow gases to escape quicker. You also find that they tend to have fewer bends in the pipework which also allows gases to pass through quicker.
FB: What are the advantages with a full system?
DP: A full system tends to be straight through with no catalytic converters, baffle plates or any form of restrictions. The objective is to increase flow and improve performance, as full exhaust systems perform better without a resonator box. A resonator – essentially an additional silencer – is designed to do just that; silence further and reduce noise. You’ll know if your exhaust system has one as it will have an almost rectangular shaped bulge in the pipes – usually situated halfway between the end can and the headers. It’s just another part that restricts the exhaust gases and hence by not having one, horse power is increased.
FB: What bikes benefit most from a new exhaust?
DP: There’s not many that won’t benefit to be honest! Whether you have an older bike and need a new exhaust to replace battered sleeves to make it look nicer, while replacing depleted wadding within the end can for better sound and performance, or whether it’s a newer bike that you wish to de-cat and personalise, both the bike and the rider will benefit.
FB: Should you remap a bike when putting a new exhaust on?
DP: This depends on a lot of things like the type of bike you have, what kind of exhaust you have and what performance you want to get from your bike. As a general rule, most slip-on end cans do not require alterations in the fuelling, because most of the tuning is developed through the headers, as this section of pipe is designed to balance the exit of gases. When fitting a race or full system it will run perfectly fine but if you choose to remap/ adjust fuelling, the benefits will be clearer in the performance of your bike. The idle will be smoother, the mid-range and torque will increase, as will top end power. You should remap a full system to correct the air/fuel ratio though, because the engine is now working more efficiently (it breathes better) and your air/ fuel ratio will now be out of alignment. Your
engine is getting more air than before, but the same amount of fuel as previously. You’ll probably hear the term ‘running lean’ in reference to this issue when you install a full exhaust. At best, this means your bike won’t run brilliantly and you’ll hear a lot of noises like small explosions in your exhaust when decelerating. At worst, your engine can be running so lean that it overheats and things start melting components, which isn’t good. It’s a small price to get your bike running at optimum performance!