REVEALED: This is the Drum Charger supercharger (kind of) that, apparently, gives you 25% more power

Okay, so the bolt-on system won’t give you quite the same power gains as a proper turbo, but it claims to give you a boost of up to 0.6 bar (8.7 psi) and some 15-25 percent more power, torque and efficiency.

Turbos and superchargers are very effective, but they’re also complex and therefore expensive systems (such as the set-up on the Kawasaki H2). They also tend to work best at high revs.

With this in mind, Italian company Alter Ego has come up with a simpler, cheaper and more practical design: the Drum Charger. It’s not unlike a turbo, in as much as it harvests leftover exhaust gas energy to pressurise the air intake. But the design is less complicated than a turbo, lacking the complex, fastmoving turbines and compressors.

Instead, the Drum Charger is a simple disc-shaped membrane. On one side of the it’s exposed to the exhaust gasses as they pass through towards the muffler, via a closed channel that comes off the main pipe. On the other side is the air intake.

When the cylinder fires, a pulse of hot exhaust gas is sent down the pipe, part of which exits out through the muffler, but part of which goes down the Drum Charger’s closed channel and pushes against the membrane. As the membrane gets pushed away from the exhaust, it reduces the volume in the cold intake chamber, increasing the pressure before that air is sent to the airbox through a series of reed valves. As soon as the exhaust pulse finishes, the membrane returns to its original position thanks to a leaf spring, bouncing the pressure wave back out into the exiting exhaust, but leaving the gas in there – so this channel never heats up beyond 50 degrees (Celsius). As it’s driven by the exhaust pulses, it’s totally synchronized to the cylinder’s combustion cycle – so, provided the drum is the optimal distance from the exhaust header (some 60-80cm, depending on the model) it will always develop its pressure charge at exactly the right time.

Alter Ego reckons that this set-up creates a boost of around 0.3 bar (4.35 psi) with a single Drum Charger, or 0.6 (8.7 psi) with a dual-membrane unit.

The downside is fairly obvious; the Drum Charger is a big chunk of plastic that needs to sit somewhere on your bike. That membrane can’t do much work unless it’s a decent size – around 220mm in diameter is enough for small capacity bikes and scooters where each cylinder is less than 250cc, while larger cylinders up to 400cc require a 270mm-diameter membrane to ensure that enough pressure is generated.

And this is all per cylinder. Each Drum Charger works exclusively on a single cylinder, making this technology extremely cumbersome once you move beyond a twin. So you’re not going to be seeing it pop up on an inline-four superbike any day soon. In fact, an 800cc twin is about as large a motor as Alter Ego thinks the Drum Charger will be able to work for. There’s no news on when we’ll be able to buy one of these kits, or how much it’ll cost, but as soon as we get that info we’ll let you know.