BMW B46/B58 vs B46TU/B58TU
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BMW B46/B58 vs B46TU/B58TU

Updated August 30, 2021

BMW introduced the B-series of modular engines in 2016. But by 2019 there was already a major overhaul of the B46 4-cylinder and B58 6-cylinder engines. The differences were significant and we feel it's necessary to detail what we have found.


First some background. The B engines are modular in design - many of the same components are shared between 4-cylinder and 6-cylinder engines. Common items include camshaft gears, sensors, and gaskets just to name a few. The modular design allows parts commonality and transfer between models, reducing development times and cost and streamlining development and inventory systems.

Second, BMW has way too many abbreviations for their engine specs. The best is the full 8-digit engine code. However, internal docs will often reference a shorthand code for some reason. But there are multiple shorthand codes that mean different things. As a new-from-the-ground-up engine family we expect there to be updates along the way, as well as a system for keeping track of the changes. However, these shorthand abbreviations just muddy the waters and create additional confusion.

Third, some translation of the full 8-digit engine code.

BB modular engine family
4 = 4-cylinder
5 = 6-cylinder
6 = turbocharged, direct injection, Valvetronic, SULEV emissions spec
8 = turbocharged, direct injection, Valvetronic
A = transverse mounting for FWD vehicles
B = longitudinal for RWD/xDrive vehicles
20 = 2.0 liter
30 = 3.0 liter
M = Mittel output, "Medium"
O = Obere output, "Upper"
0-9update version, 0 = original

Click below for an example:

BMW will then offer abbreviations that are not as clearly defined. Here are the ones we're aware of:

B46 (no suffix)
B58 (no suffix)
the original-spec B46 and B58 engines released in 2016
short engine of the original-spec B46 and B58 engines released in 2016.
Short engine = block, rotating assembly, cylinder head, but no accessories
short engine of the B46C and B58C engines released in 2017 (no major changes).
Short engine = block, rotating assembly, cylinder head, but no accessories
B46B20O0 (c. 2017-2019)
B58B30M0 (c. 2017-2019)
B58B30M1 (c. 2020+)
a Medium output engine, with or without a TU update.
The "C" only refers to the power class of the engine. It has nothing to do with the parts or components on the engine.
B58C = certain 2017-2020 models
B58CTU = certain 2020+ models (p.s. - you'll never find this code in BMW docs even though it makes sense and would clear up some confusion)
B46B20O1 (c. 2019+)
B58B30O1 (c. 2019+)
a Upper output engine, but only offered with the TU update.
The "D" refers to the power class of the engine but it was released as the TU. There were no D engines before the TU, therefore D and TU are interchangeable in BMW's eyes (for now).
B46D = B46TU
B58D = B58TU (or B58DTU or B58O1?)

You can geek out learn more about BMW engine codes by clicking here.

Model Year Changes

BMW released TU versions of the B46 and B58 starting with the 2019 model year and phased in the changes with facelift or all-new models. By the 2020 model year all of the B engines were the new TU versions (with a few exceptions). As a car owner you might not have any crossover at all but some owners will need to pay strict attention to model years and notes so they get right parts. We laid out the model changes here with this chart:

330i (F30)2016-2018B46M0
330i (G20)2019-B46O1 / B46TU / B46D
340i (F30)2016-2018B58M0
M340i (G20)2019-B58O1 / B58TU / B58D
430i (F32)2016-2020B46M0
430i (G22)2021-B46O1 / B46TU / B46D
440i (F32)2016-2020B58M0
M440i (G22)2021-B58O1 / B58TU / B58D
530i2017-2019B46O0 / B46C
530i2020-B46O1 / B46TU / B46D
540i2017-2019B58M0 / B58C
540i2020-B58M1 / B58CTU / B58C
740i2017-2019B58M0 / B58C
740i2020-B58M1 / B58CTU / B58C
840i2019-B58M1 / B58CTU / B58C
X1 28i2016-2019B46
X1 28i2020-B46TU / B46D
X2 28i2016-2019B46
X2 28i2020-B46TU / B46D
X2 M35i2019-B48TU / B48D
X3 30i2018-2019B46O0 / B46C
X3 30i2020-B46O1 / B46TU / B46D
X3 M40i2018-2019B58 / B58O0
X3 M40i2020-B58O1 / B58TU / B58D
X4 30i2019B46O0 / B46C
X4 30i2020-B46O1 / B46TU / B46D
X4 M40i2019B58 / B58O0
X4 M40i2020-B58O1 / B58TU / B58D
X5 40i2019B58M1 / B58CTU / B58C
X6 40i2019B58M1 / B58CTU / B58C
X7 40i2019-B58M1 / B58C
Z4 30i2019-B46TU
Z4 M40i2019-B58O1 / B58TU / B58D
Supra A90 6-cyl2020B58M1 / B58C
Supra A90 6-cyl2021-B58O1 / B58TU / B58D
Supra A90 4-cyl2021-B46O1 / B46TU / B46D

B46 engine bay differences.

B58 engine bay differences.

Specific Changes

So what changed? Quite a lot! The TU engines are almost brand-new designs but still modular so they fall within the B-series family. The changes were consistent with FWD and RWD-based models but our focus here is on BMW models, not MINI products. These are the differences we know of (there could be others).

The TU crankshaft is 2.3lbs lighter due to the use of lighter materials and different machining.

Timing Chain
The TU now has a 1-piece timing chain instead of a 2-piece. The original B46 design had a complicated chain-tensioner-guide rail design probably due to the layout of the accessories in the engine bay. The new design eliminates two camshaft sprockets, one intermediate shaft, two guide rails, and one chain tensioner to make the system simpler. Unfortunately it may make service more expensive since the upper half of the timing system cannot be replaced independent of the lower half. But chances are that if you need to replace a timing chain it's best to have the engine out of the car anyway.

VANOS Cam Gears
Because of the changes to the timing chain, the cam gears on the VANOS system are also different.

Serpentine Belt
The belt drive has also changed due to the revised cooling system and overall layout of the engine accessories. The belt is now shorter with fewer deflection pulleys and a simplified tensioner system. The tensioner now forms the face of the alternator, eliminating an extra pulley and saving space on the engine. Other parts of the belt drive also changed - crankshaft vibration dampener, water pump, and A/C compressor.

Cooling System
The TU engine now has an innovative cooling design that separates the cooling supply into two zones: cylinder head and engine block. Not unlike different cooling zones in your house. The cylinder head and turbo receives a constant supply of coolant but cooling to the engine block can be reduced or turned off. During a cold-start, warm-up, or normal driving coolant circulates through the cylinder head and turbo but is cut off from the engine block. Only when needed is the valve to the engine block opened, allowing coolant to circulate through the crankcase. The water pump and thermostat are now part of this Heat Management Module (but available for replacement individually).

Fuel Injectors
New fuel spray pattern and pressure is specified for the TU engine.

Engine Computer
The ECU has been updated to a newer version.

Cylinder Head-Exhaust Manifold-Turbo (B58B30M1 only)
On the B58 Medium-output engines the cylinder head casting includes an internal exhaust manifold. The usual coolant passageways are routed around the exhaust runners internal to the head. The coolant lowers the exhaust gas temperature which improves the life of the catalytic converter and uses less fuel. It also helps to increase the coolant temp faster, bringing the engine up to operating temp sooner. This has eliminated the traditional external steel exhaust manifold for a very different design. Instead of six exhaust ports on the outside there are just two, like a pair of swan necks between the turbo housing and the head. As of this time (August, 2021) this only affects standard "x40i" models - G30 540i, G32 640i, G12 740i/745e, G15 840i, G05 X5 40i/45e, G06 X6 40i, G07 X7 40i as well as the 2019-2020 Toyota Supra. The "M40i" M Sport models use the B58B30O1 engine.

B46 vs B48

Why are there two versions of the 4-cylinder engine? Short answer is that BMW wanted a performance-spec for their special models like the X2 M35i and the MINI John Cooper Works. The B46 is the Super Ultra Low Emissions spec (SULEV) and that is the standard engine in the US market. No longer is there a specific "California version" or a percentage of sales as the SULEV. Now, with the exception of the "M35i" models, all of the turbo 4-cylinders are the SULEV spec.

The B48 M35i models are more than just a boosted B46. It has a reinforced crankshaft with larger bearing surfaces, higher compression pistons, different connecting rods, larger turbo, revised fuel injectors, and better flowing intake and exhaust systems.

Z4 vs Supra

Disclaimer: we're not Toyota experts and have no access to genuine Toyota parts diagrams. The following info is what we have been able to deduce from comparing the parts, diagrams, and info already made public.

The G29 Z4 M40i was released for the 2019 model year and always had the B58O1 engine in the US market. This is the Obere, or "Upper", output spec with 382hp and was shared with G20 M340i and G22 M440i.

When the Supra was released as a 2020 model it used the B58M1 spec with 335hp (aka the Medium output). The B58M1 spec was also shared with 2020+ BMW G30 540i, G12 740i, G01 X3, G02 X4, G05 X5, and G06 X6. It was also used in the European-market Z4 M40i to meet the EU6 emissions regulations. The higher-output B58O1 was also available in European countries where the EU6 regulations did not apply.

There are significant differences between the two B58 specs - see the section above regarding the cylinder head and turbo.

Now for the 2021 model year the Supra has been granted the B58O1 engine with 382hp. We assume it's all of the same parts as the G29 Z4 M40i (but we can only assume right now).


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