Tuning the BMW B38

"Comprehensive guide to performance parts and tuning the BMW B38 engine!"

Herein we look at B38 tuning and outline the best upgrades. BMW B38 are fantastic to work on and with a few sensible motorsport modifications like ECU maps, turbo improvements and camshafts you will dramatically improve your driving fun.

Just because particular parts are are common on B38 it doesn't mean it is good, we will best parts that will give your B38 the biggest power gain return for your cash.

Significant gains on the B38 can be made from camshaft upgrades. Altering the camshaft profile alters the intake and exhaust durations on the engine and can dramatically change the torque and power output.

NB: Fast road camshafts tend to bump the power throughout the rpm range, you may sacrifice a little low end torque but your top end will be better.

Motorsport and race camshafts, bump the top end band but as a result the car will not idle smoothly and low end power nearly always suffers.

For a car driven daily one should, ideally, try to optimize your torque band to your cars usage.

I'd never have ever thought a B38 Motorsport and race camshaft is a pleasure to live with when on the daily commute.

Each engine responds better to different cam durations than others.

The engine timing and injectors and fuel pump also will make differences on the bhp gains you'll make.

A longer valve duration can alter the bhp band and on most engines the exhaust and intake durations do not need to match, although most cams and tuners use matched pairs there are some advantages to extending the intake or exhaust durations.

Stage 1 modifications: Drilled & smoothed airbox, Panel air filters, Remaps/piggy back ECU, Sports exhaust manifold, Intake headers, Fast road camshaft.

Stage 2 modifications: high flow fuel injectors, fuel pump upgrades, Fast road cam, induction kit, Sports catalyst & performance exhaust, Ported and polished head.

Stage 3 modifications: Twin charging conversions, Adding or Upgrading forced induction (turbo/supercharger), Internal engine upgrades (head flowing porting/bigger valves), Competition cam, Engine balancing & blueprinting, Crank and Piston upgrades to alter compression.

Plan your options and then acquire your modifications and set yourself a power target to save yourself from expensive mistakes.

ECU flashing allows a tuner to fully realize the full potential of all the upgrades you've fitted to your B38.

It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but your mileage usually depend much on the upgrades you've done and the condition of your engine.

Feeding air into each cylinder is the whole point to any engine performance tuning project.

Intake flow the air from the intake filter and allow it to be drawn into the engine and mixed with fuel.

The shape and flow rate of the Intake headers can make a noticeable effect on to fuel atomisation on the B38.

We often see plenum chambers are in dire need of aftermarket parts, although a few manufacturers provide fairly well optimized plenum chambers.

Big valve conversions on the B38, doing a bit of 3 or 5 angle valve jobs and porting and head flowing will also raise bhp, the fantastic side effect is it will make space for increasing the bhp increase on other upgrades.

Turbo upgrades

NASP engines need quite a lot of work when you add a turbo, so we have a separate guide to help you take into account the pros and cons of going this route on your B38

The more air you can get into an engine, the more fuel it can burn and uprating the induction with a turbocharger upgrade makes superb power gains.

When your motor has a turbo already fitted parts are more reliable and turbo charged engines will have uprated components.

However engines will need better parts at higher power limits

See where you'll find these limitations and install better pistons and crank to cope with the power.

It's not unheard of people spending a loads of money on turbocharger upgrades on the B38 only to have the B38 literally blow up soon after it's used in anger.

Larger capacity turbos often experience low end lag, and smaller turbos spool up quickly but do not have the top end torque gains.

In recent times the range of turbo units is always moving on and we are seeing variable vane turbo units, allowing the vane profile is altered according to speed to lower lag and increase top end power.

Twin scroll turbo units divert the exhaust flow into two channels and direct these at differently profiled vanes in the turbo charger. They also increase the scavenging effect of the engine.

It is not unusual that there is a limitation in the air flow sensor AFM/MAF on the B38 when a lot more air is being drawn into the engine.

You'll see that 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor sapped torque at a much lower level.

Adding a supercharger or additional turbo will make large bhp and torque gains, although more complex to setup. We have this article covering twinchargers if you want to read more.

Fuelling upgrades and mods

When you increase the bhp and torque you will need to increase to the fuel system.

More bhp and torque needs more fuel. We would recommend you to over specify your flow rate on the injectors.

The rule of thumb is to add 20% to the flow rate when buying an injector, this accounts for injector deterioration and provides some spare capacity should the engine require more fuel.

We think this one is common sense, but you'll need to match your fuel injector to the type of fuel your car uses as well.

Exhaust upgrades and mods

Only look to improve your exhaust if the current exhaust is creating a flow problem.

On most factory exhausts you should find that the exhaust flow rate is still ok even on modest power gains, but when you start pushing up the power levels you will need to get a better flowing exhaust.

Sports exhausts can help balance the flow of air through the engine.

But if your exhaust pipe is too big, ie: it's over 2.5 inches bore, you will lose much of your flow rate and end up losing power and torque.

Typically exhaust restrictions are traced to the emissions filters installed, so adding a freer flowing performance alternative will help avoid this restriction.

Weak spots, Issues & common problem areas on the B38

The B38 engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the B38, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

For more information on Tuning your B38 engine please join us in our friendly forum where you can discuss tuning options in more detail with our tuning articles to get a full grasp of the benefits and drawbacks of each modification.

History of the Engine

B38: 3 cylinder turbocharged petrol engine.

The weight of the engine makes the power feel all the more present, and the turbos can be tweaked to produce more power.

B38A12U0

  • 55 kW (74 bhp) at 4,000 rpm 150Nm(111 lbft) at 1,400–4,000 rpm
  • 75 kW (101 bhp) at 4,250 rpm 180Nm(133 lbft) at 1,400–4,000 rpm

2014–current F55/F56 Mini One First
2014–2018 F55/F56 Mini One

B38A15M0

  • 75 kW (101 bhp) at 4,250 rpm 180Nm(133 lbft) at 1,400–4,000 rpm
  • 100 kW (134 bhp) at 4,400–6,000 rpm 220Nm(162 lbft) at 1,250–4,300 rpm

2015– BMW F45/F46 216i Active Tourer / Gran Tourer
2018– F55/F56 Mini One
2015– BMW F20/F21 116i
2015– BMW F20/F21  118i
2015– BMW F22/F23 218i coupe / convertible
2014– BMW F45/F46 218i Active Tourer / Gran Tourer
2015–2019 BMW F30/F31 318i
2015– BMW F48 X1 sDrive18i
2014– F55/F56/F57 Mini Cooper
2015–2019 F54 Mini Clubman
2017– F60 Mini Countryman
2017– F39 X2 sDrive18i
2017– F45 225xe Active Tourer (PHEV)
2019– F40 118i
2019– F44 218i Gran Coupé

B38K15T0

  • 170 kW (228 bhp) at 5,800 rpm 320Nm(236 lbft) at 3,700 rpm

2013– BMW I12 i8

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