Supermotos are considered by some as the most fun you can have on two wheels. These hooligan machines, essentially dirtbikes equipped with road tires, are capable of doing some of the most insane things on two wheels, provided they’re in the control of capable hands. That being said, powerful supermotors like the GasGas EC 300 are among the best in the industry – but can they be made even better and more fun?

Sib Mustard, a German bike builder with a penchant for supermotos certainly thinks so. Having created quite the following from his custom sumo builds, Sib, with more than 160,000 followers on Instagram, operates a shop called Haisl in Upper Palatinate. His latest creation is based on a 2021 GasGas EC 300, and it goes without saying that it’s one of the wildest custom supermotos out there. Sib has taken the bike to the extreme by doubling its engine capacity while retaining the bike’s lightweight construction.


Out of the factory, the GasGas EC 300 pumps out about 50 horsepower and weighs in at just over 100 kilograms. That’s already quite the impressive power-to-weight ratio. However, Sib decided that that simply wasn’t enough. He got a racing engine from Austrian engine supplier Rübig, a brand well known in the region for its high-performance racing engines for both cars and motorcycles. Gone was the 300cc motor, and in went a whopping 699cc, two-stroke, water-cooled, single-cylinder engine. Rocking a 100 mm bore and 89 mm stroke, this engine produces 84 horsepower out of the box. The bike was then dubbed the “Megasgas EC 700.”

Sib Mustard’s Megasgas EC 700 Is A Wild Custom Supermoto
Sib Mustard’s Megasgas EC 700 Is A Wild Custom Supermoto

Managing the fueling of the powerful engine is a new Smartcarb SC2 electronic carburetor, and the engine breathes through a custom DBR Factory exhaust system which is constructed out of individually welded titanium segments. Needless to say, nothing about this bike is street legal.

Of course, major tweaks had to be made to the frame to accommodate an engine that’s almost twice the size of the original. As such, Sib had to adjust the mounting points on the frame, ensuring the bike’s balance remained straight. The result was a custom swingarm milled from aluminum, as well as a new bespoke rear shock absorber mount. In total, Sib estimates the bike to weigh in at 120 kilograms – still incredibly lightweight for a motorcycle with 80 horsepower on tap.

What’s even crazier is that Sib says the Megasgas EC 700 is still a work in progress. His next project in his Haisl will be boosting the bike with a turbocharger. It’s a well-known fact that once forced-induction comes into play, we can see power figures that are off the charts. With that, the Megasgas EC 700 breaching the one horsepower per kilogram ratio is a more than likely scenario.

Gallery: Sib Mustard’s Megasgas EC 700 Is A Wild Custom Supermoto

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