Tuning the BMW S85B50

"Comprehensive guide to tuning the BMW S85B50 engine!"

The BMW S85B50 are good project engines and with the ultimate modified enhancements like a remap, turbo upgrades and camshafts you will really improve your driving experience.

Our aim here is to review S85B50 tuning and highlight the premier modifications for your car.

The top S85B50 upgrades on an engine are in our opinion the ones that give the best value for money.

We won't be swayed by popular S85B50 upgrades, they need to be cost effective.

The camshaft profile plays a big part in the engines power output so camshaft upgrades make quite a large difference. The intake and exhaust durations will alter depending on the chosen camshaft profile, so large bhp gains are on offer for camshaft upgrades.

NB: Fast road camshafts normally increase the bhp and torque over the rpm band, you might lose a little low down power but the top end will improve.

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

For a typical daily driver must carefully try to optimize your bhp range to your preferences.

I'd never have found a S85B50 Motorsport and race camshaft is a pleasure to live with when driving around busy urban areas.

Different S85B50 engines respond better to more or less aggressive cam durations so set your engine up on a rolling road.

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

A longer valve duration can alter the power 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: Intake headers, Fast road camshaft, Remaps/piggy back ECU, Panel air filters, Drilled & smoothed airbox, Sports exhaust manifold.

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

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

Carefully think through your options and then acquire your upgrades and set yourself a power target to avoid wasting your time and money.

Mapping allows a tuner to fully realize the full potential of all the upgrades you've fitted to your S85B50.

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

Shoving more air and fuel into each cylinder is vital to any engine performance tuning project.

Intake manifold transmit the air during the suck phase from the air cleaner and allow it to be sucked into the engine and mixed with fuel.

The bore size, shape and flow rate of the Headers can make a noticeable difference to to fuel atomisation on the S85B50.

I usually find intake manifold are needing performance upgrades, although a few car makers provide reasonably well designed intake manifold.

Fitting big valve kits, getting port matching and head flowing will also lift power, and significantly will afford you increasing the power 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 S85B50

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

If your motor has a turbocharger tuning parts are simpler to install and turbo charged engines are made with harder and stronger components.

There are reliable limits for every engine, with some being very over engineered and some only able to handle stock power

Discover these limits and upgrade to forged components to handle the power.

We've seen guys spending a a stack of money on turbocharger upgrades on the S85B50 only to suffer the humiliation of seeing the car explode just after it's been enthusiastically driven.

Bigger upgraded turbos commonly experience no power at low rpm, and small turbos spool up more quickly but won't have the high rpm power band gains.

We are pleased that the range of turbos is always improving and we are seeing variable vane turbos, permitting the vane profile is altered according to speed to lower lag and increase top end power.

Twin scroll turbos divert the exhaust gases into 2 channels and direct these at differently angled vanes in the turbo. They also help the scavenging effect of the engine.

You'll commonly see there's a restriction in the air flow sensor MAP/MAF/AFM on the S85B50 when a lot more air is being drawn into the engine.

Going up you'll find 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor limited bhp at a much lower level.

Adding a supercharger or additional turbo will make large performance gains, although more complex to get working. We have this feature on twinchargers if you want to read more.

Fuelling upgrades and mods

You will need to ensure that the engine is not starved of fuel so will have to pay attention to the fuelling when you start extending past 20% of a torque increase.It is important to over specify your injectors flow rate.

As a rule of thumb add 20% to the flow rate when buying an injector, this allows for injector deterioration and provides a little spare capacity should the engine need 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

You may need to replace your exhaust if the existing exhaust is actually creating a restriction.

On most factory exhausts you'll see the flow rate is fine 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 equal out the flow of gases through the engine.

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

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

Weak spots, Issues & common problem areas on the S85B50

The S85B50 engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the S85B50, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

For more information on Tuning your S85B50 engine please join us in our friendly forum where you can discuss tuning options in more detail with our S85B50 owners. It would also be worth reading our unbiased tuning articles to get a full grasp of the benefits and drawbacks of each modification.

History of the Engine

The S85 is a naturally aspirated V10 and was the first and only production V10 engine BMW produced.

  • S85B50
  • 373 kW (500 bhp)@7,500 rpm
    520 nm (384 lbft)@6,100 rpm

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