Motorcycles

Bolt-on drum charger boosts motorcycle power and torque up to 25% - at a fraction of the cost of a turbo

Bolt-on drum charger boosts mo...
Alter Ego's Drum Charger: CAD render showing where the charger would fit on a KTM RC390 sportsbike
Alter Ego's Drum Charger: CAD render showing where the charger would fit on a KTM RC390 sportsbike
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Alter Ego's Drum Charger: exterior view
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Alter Ego's Drum Charger: exterior view
Alter Ego's Drum Charger: exterior view of scooter design
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Alter Ego's Drum Charger: exterior view of scooter design
Alter Ego's Drum Charger: interior view of scooter design
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Alter Ego's Drum Charger: interior view of scooter design
Alter Ego's Drum Charger: CAD render showing where the drum charger might fit on a Piaggio Medley scooter
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Alter Ego's Drum Charger: CAD render showing where the drum charger might fit on a Piaggio Medley scooter
Alter Ego's Drum Charger: exploded view
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Alter Ego's Drum Charger: exploded view
Alter Ego's Drum Charger: CAD render showing where the charger would fit on a KTM RC390 sportsbike
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Alter Ego's Drum Charger: CAD render showing where the charger would fit on a KTM RC390 sportsbike
Alter Ego's Drum Charger: CAD render of a drum-charged Suzuki SV650 v-twin concept
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Alter Ego's Drum Charger: CAD render of a drum-charged Suzuki SV650 v-twin concept
Alter Ego's Drum Charger: CAD render of the drum charger fitted to a Ducati Scrambler
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Alter Ego's Drum Charger: CAD render of the drum charger fitted to a Ducati Scrambler
Alter Ego's Drum Charger: dual membrane design is thicker, and thus harder to mount
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Alter Ego's Drum Charger: dual membrane design is thicker, and thus harder to mount
Alter Ego's Drum Charger: single membrane version shouldn't get in the way too much
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Alter Ego's Drum Charger: single membrane version shouldn't get in the way too much
Alter Ego's Drum Charger: dual membrane version
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Alter Ego's Drum Charger: dual membrane version
Alter Ego's Drum Charger: a range of potential designs
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Alter Ego's Drum Charger: a range of potential designs
Alter Ego's Drum Charger: benefits
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Alter Ego's Drum Charger: benefits
Alter Ego's Drum Charger: how it works
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Alter Ego's Drum Charger: how it works
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This refreshingly simple forced induction system for motorcycles won't give you the huge power output of a turbo system – but it can give you a boost of up to 0.6 bar (8.7 psi) and some 15-25 percent more power, torque and efficiency at "about a tenth" the price of a turbo setup.

If you want more power, torque and efficiency out of your motor, one of the best ways to get it is to force more air into the combustion chamber, then give it more fuel to make a bigger bang with. There's a few different ways to make this happen. You can go really fast and funnel the ambient air you're riding through into the airbox – that's ram air, and it's a staple of most sportsbike designs.

Then there's the turbine-driven methods, superchargers and turbochargers, which use spinning compressors to squash air down to high pressures. Superchargers power their compressors directly off the engine crank, sapping a little power to return lots more. Turbos power their compressors using small turbines that harness the speed of exhaust gases. Both these methods are very effective, but complex and expensive, and both tend to produce their best results at higher RPMs.

If you look at the car world, turbos are where it's at right now. As manufacturers fight to meet ever-tightening emissions regulations and fuel economy standards, car engines are generally getting smaller, using fewer cylinders and lower displacement, along with turbochargers to keep power and torque figures up in the fun zone.

But in the motorcycle world, things seem to be going the other way. There's only one forced-induction motorcycle on the market, and it caused a huge sensation when it was launched. The ball-tearing supercharged Kawasaki H2 is an incredible machine, as I found out when I left a trail of steaming Pollock-style terror stains across the roads of Southern California last year. But it's nearly twice the price of a "regular" superbike; heck, you could probably buy a new ZX-10R and throw a turbo kit on yourself for less money.

The H2 isn't built to use forced induction in a practical way, it's a hero bike designed to drop jaws, a trump card in bench racing arguments. But Italian ideas factory Alter Ego believes there's room in the market for a simpler, cheaper and more practical design.

Alter Ego's Drum Charger: exterior view
Alter Ego's Drum Charger: exterior view

The Drum Charger is superficially similar to a turbo; it harvests leftover exhaust gas energy to pressurize the air intake. But instead of using complex, fast-moving turbines and compressors, it does so in a very mechanically simple way.

The drum charger, at its heart, is a plain old disc-shaped membrane – you could think if it a bit like a speaker cone. On one side of this membrane, it's exposed to the exhaust gases 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.

Alter Ego's Drum Charger: exploded view
Alter Ego's Drum Charger: exploded view

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.

Impulse Drum Charger by AlterEgo Hardware

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 60-80 cm, depending on the model) it will always develop its pressure charge at exactly the right time.

The result? 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. This from a simple plastic drum with a carbon fiber membrane, a spring, some valves and no other moving parts. That doesn't compare with the kind of boost you can get from a turbo or supercharger – heck, the Kawasaki H2's standard blower makes up to 1.41 bar (20.5 psi) – but it's an incredibly cheap and easy way to get the same effect at a lower and more practical level where you don't have to start worrying about what grade fuel you're running.

Alter Ego's Drum Charger: CAD render of the drum charger fitted to a Ducati Scrambler
Alter Ego's Drum Charger: CAD render of the drum charger fitted to a Ducati Scrambler

The key downside is fairly obvious; the drum charger is a big ol' 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 220 mm diameter is enough for small capacity bikes and scoots where each cylinder is less than 250 cc, and larger cylinders up to 400 cc require a 270 mm diameter membrane to get enough pressure 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.

At this year's EICMA expo in Milan, Alter Ego rolled out a KTM RC390 – a single cylinder sportsbike with two single-membrane drum chargers bolted on. "With little or no engine calibration," according to a press release, this bike received an instant 15-odd percent power and torque boost across the entire rev range, with a smoother power curve that the company claims leaves the bike very usable. Here's a dyno chart.

Even though it's a chunky little blighter, at a price "about ten times lower than the cost of a turbo," the drum charger will certainly raise some eyebrows, particularly among small-capacity single cylinder sportsbike owners. The RC390 seems like pretty much the perfect bike to throw one onto as an aftermarket kit.

Such a kit would consist of the drum charger itself, plus a different exhaust pipe, a different airbox and some kind of alteration to the fuel mapping. The company says it would be simple enough for any mechanic to throw on a bike.

But Alter Ego's real intention is to sell the drum charger concept straight to manufacturers who can use it as an OEM component. A bike designed around the idea of drum charging could theoretically get rid of the airbox altogether, freeing up space for one or more chargers mounted in less inconvenient spots than "right where my leg wants to be."

The Rome-based company feels that there's an opportunity for the motorcycle world to go smaller while still generating strong power and torque figures. It's not going to revolutionize the top end of the sportsbike market, but the drum charger represents a clear opportunity to beef up what's happening in the middle and lower end sections of the market.

That's a worthy goal, and with a design this simple it's got a chance to work. We'll keep an eye on how these guys progress in the coming months.

More information: Alter Ego

13 comments
riczero-b
I'm no expert on this aspect of engines but would guess it'd need fine tuning of the connecting pipes to avoid out-of-phase effects; it could ( literally) suck instead of blow.
alan c
Drum? Don't they mean diaphragm pump?
toyhouse
Interesting concept. Looks like an novel way to tap more power from small cc off-road machines as well. As it uses a diaphragm that pulses like a drum along with the exhaust pulse, I wonder if it increases, dampens or relocates sound output? I think they should target after-market first while targeting manufacturers later as that seems a gamble and anything that makes power this way would be desired by current owners of existing machines. Hope that made sense? Just keep the price down and they'd sell a lot of them I would think.
VincentWolf
It's much more effective to just change to an all electric drive train.
Milton
I'd seriously question this before paying for it. I agree with riczero-b that timing is critical, and I doubt you could get good results otherwise. I also question heating up the air on the intake end (cold air is ideal for power).
Martin Hone
Loz reckons "Superchargers power their compressors directly off the engine crank, sapping a little power to return lots more. Turbos power their compressors using small turbines that harness the speed of exhaust gases. Both these methods are very effective, but complex and expensive, and both tend to produce their best results at higher RPMs." Superchargers sap a LOT of power from the host, and turbos use the exhaust ENERGY to spin up the turbine wheels. Superchargers work well at low to mid rpm, turbos work well mid to high rpm. I like the concept of the 'drum' system but can't see it going mainstream in its current format.
MD
Just think, now they are using WW2 German Technology.. In function this works in a similar manner to a buzz jet valve... Allowing fresh air in (at slight boost) while regulating it in one direction only. Kind of Pulse Ramming (my term, only to be reused with Permission). I wonder if the effect could be amplified by using a tuned resonance chamber [ok then the cost would start looking like a turbo, hell lets just go 2 stage turbo charging with reheat.) Don't worry Diaphragm pumps are a well understood tech, maybe, just maybe a new application here, (Is there any reason it hasn't been used B4?).
ljaques
I'd imagine that the effect would be somewhat muted from the exhaust heat, but 10% is 10%. Oogly beastie. @VincentWolf has a good idea in moving to an electric drivetrain. AND TORQUE ALL THE WAY FROM BOTTOM TO TOP. <vbg>
Arahant
people talking about out of phase effects like this is all theoretical or on paper, they have attached it to motorcycles and gotten it to work, they are planning on selling kits, seriously doubt they would do if they didnt actually know if it would work or not. I actually own a rc390, nice little one cylinder bike about same power as ninja500 with the ecu changer i have on it. I would love to strap something on there to increase the power as im getting abit bored with it, but still love the feel of the smaller bike. But the picture of one on an RC has me worried. Like the article says its where my leg should go. I think they have a good idea its still got some work to go though in terms of making it with special shapes or learning to better add it to a motorcycle. Which is why i think they are spot on with selling this to manufacturers who can work with them on the design and build the bike around it in a sense... much easier to add something like this cost effectively when designing a bike rather then an after-thought. That being said i would buy a kit if i could be reasonable convinced its not going to make sitting on the bike uncomfortable. Might help me get a few more years out of my bike.
GordonDolan
People think electric drive [plus battery pack & electronics] could compete on price with a few plastic discs? Ridiculous!