450HP MONSTER MERC

Within months of Yamaha claiming the title of the world’s most powerful mass-market outboard engine courtesy of its 425hp XTO, Mercury has stolen it back again with a new supercharged 450hp version of its 4.6-litre V8 engine. Not only does the new Mercury 450R offer an extra 25hp over the Yamaha XTO, it’s also 129kg lighter. This impressive power-toweight ratio should give even better acceleration and handling than the heavier Yamaha, especially on relatively lightweight high performance RIBs and sportsboats.

PERFORMANCE BOOST

The key to its performance is a supercharger that forces denser, pressurised air and fuel into the cylinders. Mercury has extensive experience of supercharging having used a similar set up on its previous generation of 2.6-litre straight six Verado engines. However, this is the first time it has added a supercharger to its new family of larger capacity 4.6-litre V8 engines. This helps it to deliver 40% higher torque than the already punchy Mercury 400R.

The supercharger itself is a 2.4-litre belt-driven twin scroll unit with water-cooling to reduce the temperature of the intake charge and maximise air density. A boost bypass valve automatically adjusts boost pressure to take account of the ambient air temperature and maintain peak performance regardless of weather conditions. Crucially, it is also designed to deliver maximum power and run reliably on ordinary 89 octane (95 RON) unleaded petrol rather