Why exhausts are left to the experts

FITTING an aftermarket silencer or complete exhaust system is the most common modification we make to our bikes. We do it to add a bit more power and personality, and to shed a bit of weight.

But, as you bolt on your new parts, are you wondering how a relatively small exhaust specialist can improve on something developed by a major bike maker?

Of course, the manufacturers are hamstrung by the need to meet legal noise limits (gases have to be routed through sound-deadening chambers and pipes, which also sap power).

But systems can be both road-legal and more powerful, as many aftermarket firms are proving. Surely the likes of Honda knows better than tiddlers like Akrapovic?

Actually, the truth is they don’t. To be precise, they don’t have time to know better. Even the mighty HRC – Honda’s race arm – doesn’t spend time developing its own exhausts. The GP team turns to specialist Arrow and the WSB squad uses Akrapovic – like every other works Japanese team in the series.

Colin Peabody, who imports Akrapovic exhausts through his company Performance Parts, says: ” There’s no substitute for time and development when making exhausts. The bike manufacturers just don’t have that time. ”

Peabody says Akrapovic performed 127 dyno runs when they were developing a full system for Kawasaki’s ZX-9R and subtle changes were made between every single run. Those changes could be a 5mm difference in the length of the header pipes or slight alterations to the shape of the pipe internals.

Bike manufacturers cannot afford to hold up the development of a new model just to squeeze a few more bhp out of an exhaust, whereas Akrapovic can spend weeks tweaking the system for one machine.

Peabody says: ” Exhausts may look like a mess of tubes, but there’s a lot of work and technology involved. ” And it’s a bit of a black art as no-one shares their secrets. ”

If manufacturers did find the time to develop better exhausts, they would have to pass on the costs of that development. And if they chose to use the same kind of materials you’ll find in a top-notch aftermarket exhaust, you would have to pay up to £1000 on top of the price of a new bike.

You can easily fork out more than £1000 for a full race system, but at least you have the choice of whether or not to bother.

Fitting an aftermarket end can will usually add 3-5bhp while a full system can add up to 15bhp. Akrapovic even claims to have gained a massive 17bhp from its system for Kawasaki’s ZX-12R.

Three main materials are currently in vogue: Alloy, carbon-fibre and titanium. Each has advantages. Alloy is cheap and very durable but also heavier than the other materials. Carbon-fibre is light and strong but can be damaged by heat and become brittle and porous. Titanium is both light and durable – but it’s also quite expensive. Titanium is the number one choice right now – if you can afford it.

But Peabody is realistic about why most riders buy his systems.

” Because aftermarket exhausts are made for the track, they don’t face the same noise restrictions as road-going versions, so they sound so much better. ” That’s the main attraction for many riders. ” Surely not – it’s all about that last bhp. Isn’t it?