BMW S65 Tuning

"All you need to know about performance parts and tuning the BMW S65 engine!"

In this article we detail the best approach to S65 tuning and point out the optimum mods that work.

A BMW S65 gives a fun base for your project and with carefully chosen performance upgrades like ECU maps, turbo improvements and camshafts you will really enhance your driving pleasure.

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History, Power & Specs of the Engine

It was a lovely sounding NASP V8 fitted to the M3. The S65 replaced the S54

It came as a 4.0l and 4.4 version, both sounded fantastic and perform really well.

  • S65B40 (414 hp) at 8,300 rpm 400 Nm (295 lbft) at 3,900 rpm
  • S65B44  (444 hp) at 8,300 rpm 440 Nm (325 lbft) at 3,750 rpm

There was also a motorsport version of the S65 named P65B44

Best S65 upgrades

When talking about the best ultimate for your S65 engine, we are going to concentrate on the tuning mods that give the best value for money.

Tuning the BMW S65 and best S65 performance parts.

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

Fast road camshafts tend to increase the performance over the rev band, you could sacrifice a little bottom end bhp but higher rpm power will be better.

Competition camshafts, increase the higher rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.

On a car driven daily you need to match your torque band to your typical driving style.

I'd be shocked if you have ever thought or claimed that a S65 Race cam is a pleasure to live with when in heavy traffic because low end power will be very lumpy. Competition cams are designed for maximum power at the top end of the RPM range, a place that most daily commutes will not permit!

Some S65 engines respond better to more or less aggressive cam durations check your engine on a rolling road.

The engine timing and fuelling also will make differences on the bhp gains you'll get.

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.

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Best mods for your S65

  1. Turbo upgrades - A New Turbo is the most dramatic method to improve intake air supply, which permits you to utilize more fuel and make power gains. Although one of the most complex upgrades it does provide the largest gains.
  2. Lightened Flywheels - a lower weight flywheel will enhance the engines ability to rev freely. Not a great mod for all S65 engines.
  3. Air Induction kits and Sports Exhausts - Please note that on their own these mods will NOT ADD PERFORMANCE for most setups, but they enable you to release power after other mods by lessening the restriction.
  4. Fast road Camshafts are are often the best upgrade for an engine, but we recommend they be installed by someone familiar with setting them up on your car and tracking one down may be hard but there is usually a local firm to regrind a stock cam for you.
  5. Engine Tunes - A tune/remap gives the most power compared to cost, aftermarket ECUs, and inline Tuning boxes are all alternatives.
  6. Flowing and porting the engine head - for larger gains, you will get better flow and make a more efficient engine if you do this to support your other mods.

S65 Tuning Stages

Typical stage 1 mods often include: Fast road camshaft, Remaps/piggy back ECU, Sports exhaust header/manifold, drilled & smoothed airbox, Intake manifolds, Panel air filters.

Typical stage 2 mods often include: Sports catalyst & performance exhaust, Fast road cam, Ported and polished head, fuel pump upgrades, induction kit, high flow fuel injectors.

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

Carefully think through your options and then find your tuning parts and set yourself a power target to avoid disappointment.

ECU mapping helps release the full potential of all the parts you've fitted to your S65.

(In some cases, as the factory ECU is locked flashing is not an option, so an aftermarket ECU is the route to take, and many of these will outperform factory ECU's but make sure it has knock protection and that you get it setup properly.)

It will usually give you around 30% more power on turbocharged vehicles and you can expect to see around 15% on NA (naturally aspirated) engines, but figures achieved usually depend much on the parts you've fitted and the condition of your engine.

It is the aim to any engine performance tuning project to force more air and fuel into each cylinder

Intake manifold flow the air from the air filter and allow it to be pulled into the engine cylinders with fuel for the squish phase.

Shape and rate of flow of the Intake manifolds can make a big improvement to fuel atomisation on the S65.

We often see air intake manifolds are begging for aftermarket parts, although a few manufacturers provide well optimised air intake manifolds.

Adding a S65 larger valve kit, doing a bit of port matching and head flowing will also lift power, and significantly will permit increasing the power increase on other parts.

S65 Turbo upgrades

NA (naturally aspirated) 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 S65

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

There are tuning limits for every engine, with some being over specified and some only just able to handle stock power and the S65 is actually pretty well tuned from the factory.

It is important to find these restrictions and upgrade to stronger pistons, crank and engine components to utilize the power.

It's not unheard of car owners spending a lot of money on turbo charger upgrades on the S65 only to see the whole thing throw a rod when it's been completed.

You'll commonly see there is a limitation in the air flow sensor AFM/MAF on these engines when loads more air is being fed 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 and torque at a much lower level.

Adding a supercharger or additional turbo will make large power gains, although harder to setup. We have a twincharger power adding guide if you want to read more.

S65 Fuelling Mods

Don't dismiss the need pay attention to the fuel system when you are increasing the bhp and torque - it makes the car more thirsty. It is important to over specify your injector capacity.

As a rule of thumb add 20% when specifying an injector, helps cope with injector deterioration and allows some 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.

S65 Performance Exhausts

You should look to increase your exhaust if your current exhaust is actually creating a flow problem.

On most factory exhausts you'll find your flow rate is good 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 usually air flow from the engine but do not go too large or you might just stuff your flow rate and make things worse. So generally speaking, keep to a size of 1.5 to around 2.5 inches to maximise flow rates, and this should take into account the amount of air your engine is moving.

Typically exhaust restrictions are in the catalysts installed, so adding a faster flowing race alternative such as a sports catalyst pretty much removes this restriction, thanks to it's larger size and surface area, and will effectively raise the performance to levels you would expect without having a catalyst installed, but keeps the car road legal.

Weak spots Issues & problem areas on the S65

The S65 engines are generally reliable and solid units, as long as you follow the manufacturers service schedules, and use a good quality oil to ensure longevity. Few problems should happen as long as they are regularly serviced and maintained.

Carbon build up in the head, particularly around the valves which will sap power or create flat spots, this is a larger issue on direct injection engines but should be looked out for on all engines. We have tips on removing carbon build up.

Some of our members have had issues with flat spots or glitches after applying mods and upgrades or tuning, this is not usually related to this engines design, so instead see our article on diagnosing flat spots and problems after tuning which should help you get the bottom of this issue.

Don't drive it hard until it's warmed up and don't drive it like a high revving turbo car on the redline all the time and it'll last forever.

Gaskets on the valve cover can leak a little oil, you might even smell burning oil as it drips over the hot engine. The heat from the engine causes this and is not a major cause for concern.

Regular oil changes are vital on the S65, especially when tuned and will help extend the life and reliability of the engine.

There was a rob bearing wear issue that led to a few engines failing, this problem is not as common as you'd think looking around, but it is very well documented. If the engine has a tick tick noise at tickover or at low to mid rpms get this checked.

Throttle bodies can fail, and you'll get the EML and DSC lights come up if you didn't realise the car was in Limp home mode.

Rough idling is often down to a faulty idle control valve, which can also cause cold start issues and misfires when under load.

If you would like to know more, or just get some friendly advice on Tuning your S65 engine please join us in our friendly forum where you can discuss tuning options in more detail with our owners. It would also be worth reading our unbiased tuning articles to get a full grasp of the benefits and drawbacks of each modification.

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