B48 Complete Build Guide


B48s come in a few configurations. Identifying which one you have will help you choose the correct mod path. Bimmercat helps you determine what engine you have according to your vin. All "B48s" in the United States are SULEV and therefore have a different designation known as the B46. Both engines are practically identical but it is important to note when buying a downpipe they are different. 

B48A/B46A: 11.0:1 Compression 181bhp/200ft-lbs Stock (20i/30e Models)

B48B/B46B: 10.2:1 Compression 248bhp/295ft-lbs Stock (30i Models 2017-2018)

B48TU/B46TU: 10.2:1 Compression 255bhp/295ft-lbs Stock (30i Models 2019+)

B48E (TU Variant): 9.5:1 Compression 301bhp/332ft-lbs Stock (35i Models 2019+)

Warning to B48/46A users:

Due to the high compression of the engine, many have experience low speed pre-ignition and cause severe damage to the engine. The B48/46A engine uses weaker pistons and can crack easily. If you are modifying/tuning your car, we recommend to religiously keep up with maintenance and only use the best quality fuel. People that live in countries with bad fuel quality have higher risk of blowing the engine. This does not mean you cannot modify your car, many have had success but it is something to note that this variant of the B48 is weaker.


Cold Air Intake (CAI)


Offered by many companies such as MST, Injen, BMS, Dinan, etc. CAI free up air flow restrictions. They provide negligible performance gains but since they remove factory silencers you will hear the turbo spool and flutter. CAI are usually paired up with stage 1 tunes. 



Offered by many companies like us, VRSF, Evolution Racewerks, MAD etc. Downpipes can come catless or catted. Catted downpipes are usually twice as expensive and do not provide as much power gain. Catless downpipes will provide the most gain. It is important to note if you go catless their is a risk of exhaust odor.  A catless B46 odor is barely noticeable. Whether it is catless or catted, downpipes are necessary for a stage 2 tune. You can purchase one here 



Gen 1 B48/B46s are able to use a B58TU/B46TU HPFP. 2019+ B48/B46s already have the HPFP from factory. The stock fuel system can handle up to an e50 mix. This will allow you to run a full E85 tune. You can purchase one here.

Gen 1 B4xs also have the ability to run the IPOSMotorsport Stage 1 and Stage 2 HPFPs. These have a higher flowing capacity over the B58TU HPFP and therefore support more horesepower.

Turbo Upgrades

Due to the majority focus on B58s, there are not a lot of options for turbo upgrades. Gen 1 B48/46s used a Mitsubishi TD04LR-5.6T. Gen 2 B48/46s use a Garret MGT2056. 

IPOSMotorsport IM450/IM500- Recasted turbochargers with bigger housings. No core charge required since they are brand new turbos. Two options available to suit different builds ranging from high 300s to low 500whp. These are by far the best turbochargers available on the market. You can purchase one here

Pure Turbo- Pure turbo offers a hybrid turbo upgrade using the stock turbo frame. This means that you will need to send in your turbo or pay a core deposit and they will fit a larger compressor/turbine wheel. Although they claim the turbo supports 400whp, hybrid turbos attempt to push out as much power out the stock frame turbo resulting in increased stress on the turbo and engine.

Power: 360-380whp depending on fuel

Big Boost Turbo- The big boost turbo upgrade is a complete kit including a new turbo, oil/coolant lines, downpipe, chargepipe, and intake pipe. Big boost claims their kit can support 500whp+ but third party testing has revealed that it is nowhere near that. Big boost advertises the twin-scroll functionality but the turbo is single-scroll along with a half done twin-scroll manifold. We do not recommend getting this turbo upgrade. 

B48E Turbo- This is an OEM turbocharger found in the B48E models. Can support up to 380whp. This is an easy swap for B48s that are transverse like in the Mini Cooper models. If you have a longitudinal BMW you will need a custom charge pipe and intake to make it work. 



Common tuning platforms include BM3, MG Flasher, and JB4. BM3 and MG Flasher are both flash tunes meaning you can tune your car straight from your phone or laptop. JB4 is a piggy back and you will need to connect a device to your DME. All tuning platforms offer various different types of fuel including ethanol blends up to E40.