BMW S14 Tuning

"All you need to know about performance parts and tuning the BMW S14 engine!"

The BMW S14 really good project engines and with carefully picked sports modifications like ECU maps, turbo upgrades and camshafts you will really enhance your driving enjoyment.

This engine was born from an M10 engine who had a baby with an S38 (where the head design came from less 2 cylinders of course!)

It's dual throttle bodies work a treat when correctly balanced, and the S14 was one of the last BMW engines you could tune up at home, thanks to it's mechanical simplicity and sheer solidity.

Let us examine S14 tuning and show the best modifications.

History of the S14 Engine

S14B20 

  • 1987-1990 E30 320iS (Italy and Portugal only)
  • (189 bhp) at 6,900 rpm 210 N⋅m (155 lbft) at 4,900 rpm

S14B23

  • 1986-1991 E30 M3
  • (212 bhp) at 6,750 rpm 230 N⋅m (170 lbft) at 4,600 rpm
  •  (192 bhp) at 6,750 rpm 230 N⋅m (170 lbft) at 4,750 rpm 1986–1989
  •  (197 bhp) at 6,750 rpm 240 N⋅m (177 lbft) at 4,750 rpm

S14B23 EVO2

  • 1988-1990 E30 M3
  •  (217 bhp) at 6,750 rpm 245 N⋅m (181 lbft) at 4,750 rpm

S14B25 EVO3

  • 1989-1990 E30 M3 
  • (235 bhp) at 7,000 rpm 240 N⋅m (177 lbft) at 4,750 rpm

The S14 engine came with dual throttle bodies and this helped raise the power output compared to a single throttle body design.

They can be tricky to balance correctly but it is worth the effort, and if the idle is rough or power is down this should be the first area you check.

Tuning the BMW S14 and best S14 performance parts.

Best S14 parts

Just because particular upgrades are are common on S14 it doesn't mean its worth having, so we'll best upgrades that will give your S14 the biggest power gain return for your cash.

Interestingly when BMW wanted to increase the power output, they opted to increase the displacement.

By stroking the engine we can achieve similar results and if you opt to lower the compression ratio whilst doing this you have a wider choice of turbo upgrades.

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 torque gains are on offer for camshaft upgrades.

Fast road cams usually increase the bhp through the rpm range, you might lose a little low end bhp but high end rpm power will be better.

Race cams, increase the high end rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.

For a car used daily should ideally to match your engines power to your typical driving style.

I'd never have ever thought a S14 Competition camshaft is a pleasure to live with when on the daily commute.

Different S14 engines respond better to different cam durations than others.

The engine timing and fuel pump and injectors also have a large bearing on the torque gains you'll achieve.

A longer valve duration can alter the torque 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.

For NASP engines please watch our video which covers the 5 principles of tuning your S14. Be sure to subscribe and support our new channel.

Best mods for your S14

  1. Tunes - S14 remapping provides the most power compared to your outlay, aftermarket ECUs, and Tuning boxes are all alternatives.
  2. Fast road cams are are often the best upgrade for an engine, but they must be installed by someone who knows what they are doing and tracking one down can be a challenge but there might be a local firm to regrind a stock camshaft .
  3. Flywheel lightening - a reduced weight flwheel will improve the engines ability to rev freely. But not always suitable for all S14 engines.
  4. 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.
  5. Stroking the engine - there is no replacement for displacement as they say and this is true of the S14.
  6. Air Induction and Exhaust Upgrades - NB: on their own these mods will NOT ADD POWER in most cases, but they can help lift power after other mods by lessening the restrictive flow.

S14 Tuning Stages

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

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

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

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

Remaps (piggy back ECU's and aftermarket ECU's) helps fully realize the full potential of all the upgrades you've done to your S14.

It will usually give around 15% on NASP engines, but your results will depend much on the upgrades you've done and the condition of your engine.

It is the whole point to any tuning task to push air into your S14

Intake manifolds carry the air during the suck phase from the air filter and allow it to be drawn into the engine cylinders.

The size of bore and shape and flow rate of the Plenum can make a noticeable difference to to fuel mixing and power on the S14.

We often see manifolds are ripe for aftermarket parts, although a few manufacturers provide well optimised headers.

Increasing the S14 valve size, getting S14 port enlargement and head flowing will also improve power, and significantly will afford you an improved power increase on other modifications.

Turbo upgrades for the S14

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 S14 but low boost turbo installations seem to work quite well, but we would recommend lowering the compression ratio, and running a higher octane fuel.

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

See where you'll find these limitations and fit better quality components to utilize the power.

Big capacity turbo chargers tend to suffer low end lag, and little turbo chargers spool up much more quickly but don't have the high rpm torque gains.

Over the last 20 years the choice of turbochargers is always evolving and we now see variable vane turbochargers, allowing the vane profile is altered according to speed to lower lag and increase top end power.

Twin scroll turbochargers divert the exhaust gases into 2 channels and flow these at differently profiled vanes in the turbo charger. They also increase the scavenging effect of the engine.

It is common that there is a limit in the air flow sensor AFM/MAF on the S14 when considerably more air is being pulled into the engine.

We see 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor was restricting torque at a much lower level.

Adding a supercharger or additional turbo will make large bhp and torque gains, although more challenging to install. We have this feature on twinchargers if you want to read more.

S14 Fuelling improvements

You will need to ensure that the engine is not starved of fuel so should ramp up the fuelling when you start extending past 20% of a torque increase.It makes sense to be generous with your injector capacity.

As a rule of thumb add 20% capacity when specifying an injector, which takes into account injector deterioration and affords a bit of 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.

All the following flywheel power targets will assume an injector duty cycle of 80% and a base of 58psi of fuel pressure at idle.

4 Cylinder turbocharged engines

  • 58 PSI 340cc/min 200hp
  • 58 PSI 511cc/min 300hp
  • 58 PSI 682cc/min 400hp
  • 58 PSI 1022cc/min 600hp

5 Cylinder turbocharged engines

  • 58 PSI 273cc/min 200hp
  • 58 PSI 409cc/min 300hp
  • 58 PSI 545cc/min 400hp
  • 58 PSI 818cc/min 600hp

4 Cylinder NASP engines

  • 58 PSI 285cc/min 200hp
  • 58 PSI 426cc/min 300hp
  • 58 PSI 568cc/min 400hp
  • 58 PSI 853cc/min 600hp

4 Cylinder supercharged engines

  • 58 PSI 312cc/min 200hp
  • 58 PSI 468cc/min 300hp
  • 58 PSI 625cc/min 400hp
  • 58 PSI 937cc/min 600hp

S14 Exhaust upgrades

Only look to replace your exhaust if the current exhaust is actually causing a restriction in flow.

On most factory exhausts you'll see the exhaust 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.

Please don't run with the widest exhaust you can find you'll slow up the exhaust flow rate - the best exhausts for power gains are usually between 1.5 to 2.5 inches. It is the shape and material more than the bore size.

Usual exhaust restrictions are in the catalysts installed, so adding a faster flowing sports alternative will help avoid this restriction.

Weak spots, Issues & problem areas on the S14

The S14 engines are generally reliable and solid as long as they are regularly serviced and maintained.

Oil changes are particularly important, the conrod bearing bing the usual area of impact for wear if this is not correctly carried out proving to be an expensive repair. In most cases wear occurs on the conrod bearing shells so keep an eye on this as the milage starts creeping past the 100,000 miles and replace them.

The spring on the timing chain tensioner causes rattling and as it wears will result in wear on the timing chain gears. Fitting an S52 tensioner would appear to be the way to go.

If you note an oil leak it will probably be the thermostat cap being the culprit. Leaks can also happen around the oil filter manifold gasket and engine.

Regular oil changes are vital on the S14, especially when tuned and will help extend the life and reliability of the engine.

For more information on Tuning your S14 engine please join us in our friendly forum where you can discuss tuning options in more detail with our S14 owners. It would also be worth reading our unbiased tuning articles to get a full grasp of the benefits and drawbacks of each modification.

Please help us improve these tips by sending us your feedback in the comments box below.

We love to hear what our visitors have got up to and which parts work best for them on each model of car. Comments are used to improve the accuracy of these S14 articles which are continually updated.

Check out my YouTube channel, we're regularly adding new content...


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