BMW B38 Three Cylinder Turbocharged Engines

BMW B38 1.5 engine in a one series

B38 1.5 in a one series.


The B38's 1.2 variant is the smallest BMW car engine since the BMW 700, a car first sold in 1959 and powered by a motorbike engine in the rear. So why is BMW now making three cylinder 1.2 and 1.5 engines? Well one reason is emissions, it's getting tougher and tougher to comply with legislation such as EU6 so efficiency must rise. This didn't happen ten years ago not for technological reasons but because efficiencies like those used on the current engines are expensive and sometimes have undesirable consequences for reliability (such as direct injection and exhaust gas recirculation). But fear not, these are BMW engines worthy of the name and as is so often the case BMW is leading the market.

BMW's design strategy is to build 3, 4 and 6 cylinder engines with very similar technologies and just a different number of cylinders. The base case is for each cylinder to displace 500cc and so give 1.5, 2.0 and 3.0 engines. All have turbos, Valvetronic and double VANOS. This makes sense from engineering, maintenance and financial perspectives.

In the case of the B38 it's first use was in 2013 as the secondary propulsion for the revolutionary i8 electric car, this was a 1.5 litre. In 2014 the 1.2 was offered in the MINI in two states of tune. The 1500 was sold in the same year on the MINI Cooper and the 118i, 218i, 318i, X1.

BMW B38 engine stripped down

B38 stripped down.


These engines employ the technologies you'd expect from the current engines. All alloy construction, Valvetronic, direct injection and dual VANOS. The compression ratio is a fairly high 11:1, that really is high for a turbocharged car.

The turbo is a single scroll unit which, unusually, is made by co-operation with Bosch-Mahle. It'd be difficult to make a twin scroll turbo work with an uneven number of cylinders. The turbo is water cooled, not oil cooled. It has a cast aluminium rather than steel housing. This was an industry first and made the unit 30% lighter as well as reducing the thermal load on the catalytic converter.

To ensure smoothness a balancer shaft is fitted which rotates at twice the crankshaft speed, something BMW first did with the M43TU 14 years earlier. Automatic models have a multi-stage damper to further reduce low rpm vibrations. There has been an emphasis on weight saving using magnesium and on quietness using acoustic shielding. The acoustic shields also double as thermal insulation, this makes the engine warm up faster and retain heat when left.

The single row timing chain is at the back of the engine. When installed in a rear wheel drive configuration this makes access very difficult in the unlikely event it becomes a problem. The oil pump is chain driven (as usual) and also at the back of the engine. It has it's own chain tensioner and guides. The high pressure fuel pump is now driven from the camshaft and not by the timing chain.

Power differences between units of the same capacity are down to the camshafts, programming and turbo boost. Higher power units also have larger intercoolers.

Just because this is a three cylinder unit BMW haven't skimped on the engineering. On the contrary, they've had to innovate in order to meet customer expectations and meet environmental laws.

BMW B38 engine in a MINI

B38 in a MINI.


Code Size Power
Made Bore x
Timing Weight
B38 1.2
101 @ 4250
74 @ 4000
130 @ 4400
230 @ 5800
130 @ 1400-4000
110 @ 1400-4000
160 @ 1250-4300
240 @ 3700
2013 on 78x83.6
Chain ? Dual


BMW B38 engine is the secondary engine for the BMW i8

The B38 1.5 is the secondary engine for the i8.


As they're direct injection they may build up deposits on the intake valves which must be manually cleaned. Most modern engines suffer from this problem, not just BMWs.

Clean oil is vital to the life of a turbo engine. As these engines have extended oil change intervals it's vital the correct long life oil is used. It's expensive so beware of cheap substitutes. Now more than ever the service history matters when buying used cars. Personally I'd change the oil before the recommended interval as I think it's too long.