BMW N52 straight-six – lightweight and modern engine

Engine guide – Inside the N52 straight-six. A look inside this high-tech, lightweight straight-six. Words: Elizabeth de Latour. Photos: BMW, ECS Tuning.

The BMW N52 straight-six was designed to replace the M54 and was introduced in 2004, remaining in production until 2011. The engine made its debut in 258hp, N52B30 form in the E63 630Ci and was joined by the N52B25 in 2005; the larger engine had five differing power outputs while the smaller variant was made available in three different versions. As with the M54, the N52 appeared in a huge range of BMW models, including the E9x 3 Series, E60, E85 Z4, E83 X3, E65 7 Series and even the F10 5 Series and F25 X3. The engine was replaced in 2011 by the N53, though not in North America where the N52 continued to be used until the turbocharged N20 was introduced, and China, where the N52 continues to be used in the F18 long wheelbase 530Li Saloon.

The N52 came in two flavours: the N52B25 used a bore of 82mm and stroke of 78.8mm with an 11.0:1 compression ratio, while the N52B30 used an 85mm bore and 88mm stroke with a lower compression ratio of 10.7:1.

The N52 used an engine block which used magnesium and aluminium for the crankcase; magnesium is extremely light, but it is at greater risk of corrosion from water and it can creep under load at high temperatures. For this reason, pure magnesium or magnesium as a conventional alloy is not suited for dealing with the sorts of loads and forces that central engine components have to deal with. Because of this, BMW employed a magnesium alloy for the crankcase shell, while an aluminium inner block was used to counteract the disadvantages of the magnesium. The N52 used Alusil cylinder liners and featured Valvetronic and Dual VANOS.

While capacity never changed, outputs varied drastically across the range for both engines, with changes in power coming from different resonant intake manifolds and different software maps. The least powerful variant was the 177hp version which was used in the Canadian E90 323i, E60/1 535i, except North America, and the 2.5i E85 Z4. Peak power was developed at 5800rpm while peak torque of 170lb ft was available between 3500- 5000rpm. The most powerful 2.5 was the 218hp version, as fitted to a number of 25i models, including the E83 X3, E9x 325i and E85 Z4 2.5si, with peak power being produced at 6500rpm and peak torque of 184lb ft available between 2750-4250rpm. The least powerful 3.0 version, as found in the E85 Z4 3.0i, North American F10 528i and X1 xDrive25i, also made 218hp, which arrived at 6100rpm, with 199lb ft, developed between 2500-4250rpm. At the other end of the scale sat the 272hp variant, with peak power being developed at 6650rpm, while peak torque of 232lb ft was produced at 2750rpm.

Tuning

If you have an N52-powered BMW, the simple fact is that you’re not going to get much of an increase in power so there’s no point in spending a fortune chasing it. A remap is the only real option that’s worth pursuing and even then that’s debatable; plenty of companies will provide you with a remap and you can expect an additional 10-15hp, which isn’t much to write home about, but it should also improve throttle response and make the car feel perkier.

For American readers, the less powerful 25i and 28i variants of the engine, along with the 218hp version of the Z4 3.0i, can be improved by fitting the three-stage intake manifold from the 258hp version of the 30i as found in the E9x models. The three-stage manifold features electronic valves that redirect airflow to the cylinders that require it most at any given moment. A couple of companies, including Turner Motorsport and ECS Tuning, sell an upgrade kit, which includes the manifold and a remap, and will take power up to 260hp – prices vary from just over $1200 to around $1700, but the gains are impressive and you’ll definitely notice a difference.