The Mitsubishi 4B1 engine is a range of all-alloy straight-4piston engines built at Mitsubishi's Japanese "World Engine" powertrain plant in Shiga on the basis of the Global Engine Manufacturing Alliance. Although the basic designs of the various engines are the same, their exact specifications are individually tailored for each partner. The cylinder block and other basic structural parts of the engine were jointly developed by the GEMA companies, but the intake and exhaust manifolds, the cylinder head's intake and exhaust ports, and other elements related to engine tuning were independently developed by Mitsubishi. All engines developed within this family have aluminium cylinder block and head, 4 valves per cylinder, double overhead camshaft layouts, and MIVECcontinuous variable valve timing. All variations of 4B1 engine share the same engine block with a 96 mm bore pitch. The difference in displacement is achieved by variance in bore and stroke. The 4B1 engine family is the first to have the continuously variable valve timing MIVEC system applied not only to its intake valves but also to its exhaust valves. The intake and exhaust cam timing is continuously independently controlled and provide four optimized engine operating modes.
The bore and stroke of the engine both measure, which engineers refer to as square. According to Mitsubishi, the new cylinder dimensions contribute to a free-revving character, linear power delivery and wide torque curve. Mitsubishi used a timing chain instead of a belt for better reliability and iridiumspark plugs to lower emissions and to help extend major service intervals for lower cost of ownership. To reduce weight, Mitsubishi used a plastic cam cover and intake manifold and double-layer stainless steelexhaust manifold. The exhaust manifold has a rear location on the transverse engine, compared to the front location for the previous engine, yielding important benefits such as better emissions performance. To lower vibration, Mitsubishi used a 4-point inertialaxis system with cylindrical hydraulic engine mounts on the left and right sides. A lightweight, high-rigidity squeeze-cast aluminium bracket on the right side mount lowers engine noise under acceleration. A lightweight, high-rigidity steel plate bracket on the left side mount lowers gear noise. A custom-tuned insulator was developed for the front and rear mounts to help control both idle vibration and acceleration shock. For the Mitsubishi Outlander PHEV, a modified variant of the 4B11 is adopted. The MIVEC VVT system is only applied on the intake side, a balancer shaft derived from the 4B12 is adopted, a linear Air/Fuel sensor fitted in place of the Oxygen sensor of front intake, unsymmetrical piston skirts, different pattern piston skirt resin coating & a unique resin coating crank shaft bearing is used. The PHEV 4B11 is restricted to a maximum operating speed of 4500 rpm to prevent damage to the electrical motors & generator from overspeeding.
Peak power and torque figures of and are for Japanese market Lancer Evolution models and figures of and are for US market models. The 4B11T is the first engine in the Lancer Evolution series that uses a die-cast aluminium cylinder block versus the cast-iron block used in the previous turbocharged4G63 engine that powered all previous models. The engine weight has been reduced by 12 kg compared to the 4G63, even with the addition of a timing chain instead of a belt and MIVEC continuous variable valve timing on both the intake and exhaust camshafts. A revised turbocharger offers up to 20-percent quicker response at lower engine speeds compared to previous 4G63. The 4B11T offers a broader torque curve, producing more torque than the 4G63 at all engine speeds, helped by the engine's square bore and stroke design, both measure. Redline tachometer hashes start at 7,000 rpm, with a fuel cutout at 7600 rpm to protect the engine. A semi-closed deck structure, an integrated ladder frame and four-bolt main bearing caps contribute to engine strength, durability, and lower NVH levels. Unlike the 4G63, the 4B11T does not use a balancer shaft. The semi-floating pistons of the 4G63 have been replaced with fully floating pistons for the 4B11T. Aluminium is also used for the timing chain case and cylinder head cover. The engine features an electronically controlled throttle, an isometric short port aluminium intake manifold, and the stainless steel exhaust manifold is positioned at the rear of the engine. The use of a direct-acting valvetrain eliminates the need of the roller rocker arm configuration previously used in the 4G63. The 4B11T features built-up hollow camshafts and its valve stem seals are integrated with the spring seats. The internal components of the 4B11T engine have been reinforced to withstand high levels of boost.
The cylinder head intake and exhaust ports and intake and exhaust manifolds are shape optimized for better volumetric efficiency. Mitsubishi lowered the friction of the engine by including elastic grinding of the valve stems, adopting a high-efficiency shroud equipped plastic impeller in the water pump and using 0W-20 low-viscosity oil. Mitsubishi increased the combustion efficiency by optimizing the design of the cylinder head intake and exhaust ports, by incorporating the MIVEC system on both intake and exhaust valves and by using injectors that give an ultra micro droplet fuel spray. To lower the engine's weight, Mitsubishi used die-cast aluminium for the cylinder block, plastic for the cylinder head cover and intake manifold, and stainless steel for the exhaust manifold. The engine features a compact balancer shaft module with an integrated oil pump. A silent chain is used to drive the camshafts. The compact balancer module, the silent chain, the stable combustion yielded by the intake and exhaust MIVEC system, and high rigidity designs for the cylinder head and cylinder block realize low vibration and noise.
