Tuning the BMW N18

"Comprehensive guide to performance tuning the BMW N18 engine!"

The BMW N18 are popular engines and with the optimum tuning enhancements like remaps, turbo upgrades and camshafts you will definitely enhance your driving opportunities.

Our aim here is to review N18 tuning and provide tips on the ultimate mods that work.

The best N18 modifications on an engine are usually the ones that give the best value for money.

We won't be swayed by popular N18 modifications, they need to be cost effective.

Altering your N18 cam will make a dramatic difference to the engine torque. Choosing a higher performance cam profile raises the torque accordingly.

NB: Fast road camshafts tend to bump the bhp and torque across the rev range, you may lose a little bottom end torque but top end will be lifted.

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.

On a car used daily you need to optimize your bhp range to your cars usage.

I'd never have found a N18 Motorsport and race camshaft is a pleasure to live with when driving around busy urban areas.

Different N18 engines respond better to more or less aggressive camshaft durations so view each engine as unique.

The ECU mapping and injectors and fuel pump also have an effect on the torque gains you'll hit.

Extending exhaust or intake durations 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.

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

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

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

The N18 engines are fantastic to work on and thanks to their popularity there is a lot of modifications and performance parts out there.

Mapping allows a tuner to fully realize the full potential of all the upgrades you've fitted to your N18.

It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but figures achieved will vary depending on the upgrades you've carried out and the condition of your engine.

Forcing fuel and air into the N18 engine is the whole point to any engine tuning task.

Intake manifold take the air from the filter and allow it to be sucked into the engine cylinders.

The shape and rate of flow of the Intake manifold can make a substantial improvement to fuel atomisation on the N18.

On popular production engines plenum chambers are needing performance upgrades, although a few car makers provide reasonably well designed plenum chambers.

Larger N18 valves, doing a bit of port matching and head flowing will also increase torque, and significantly will allow you to get an improved torque increase on other modifications.

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 N18

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

When your car has forced induction tuning mods are more reliable and you will discover turbocharged engines already contain harder and stronger components.

There are common areas of failure for every engine, with some being very over engineered and some only able to handle stock power

We recommend you find these limitations and upgrade to stronger pistons, crank and engine components to cope with the power.

There are many tuners spending a a stack of money on turbo upgrades on the N18 only to watch the whole thing throw a rod just after it's been finished.

Big turbochargers often suffer low end lag, and little turbochargers spool up more quickly but don't have the top end bhp gains.

Thanks to new tech the world of turbo units is always improving and we are seeing variable vane turbo units, allowing the vane profile is altered according to speed to lower lag and increase top end bhp.

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

You'll commonly see there is a restriction in the air flow sensor MAP/MAF/AFM on the N18 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 was restricting performance at a much lower level.

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

Fuelling upgrades and mods

Don't miss you'll need to look at the fuel delivery when you are increasing the power - it makes the car more thirsty. We would recommend you to be generous with your flow rate on the injectors.

The rule of thumb is to add 20% to the flow rate when fitting an injector, which takes into account injector deterioration and gives you 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

You only need to to boost your exhaust if your current exhaust is actually creating a restriction.

On most factory exhausts you'll see the exhaust flow rate is still 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 will certainly help air flow through the engine but do not go too big or you could will reduce the flow rate. Stick to 1.5 to 2.5 inches for best results.

Usual exhaust restrictions are in the catalyst and filters installed, so adding a freer flowing high performance alternative will help avoid this restriction.

Weak spots, Issues & common problem areas on the N18

The N18 engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the N18, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

Carbon build up has been noted, and we recommend a good regular thrash with some BG fuel cleaner to keep on top of things.

History of the N18 Engine

The partnership between BMW and the PSA group gave life to the prince engine, which BMW developed and installed in the Mini. See the PSA prince tuning article for more on this engine.

The Prince engine design won many awards for it's class taking home the title 8 years in a row.

The N18 replaced the older N14

The BMW engine now uses Double Vanos in addition to it's predecessors tech list of, direct injection, valvetronic and twin scroll turbo charger technology.

Having all of this included in this engine makes the engine quite lively and retains good class leading emissions and economy.

For more information on Tuning your BMW engine please join us in our friendly forum where you can discuss N18 tuning options in more detail with our N18 owners. It would also be worth reading our unbiased BMW tuning articles to get a full grasp of the benefits and drawbacks of each modification.

We need your help improving this article, so please send us your feedback in the comments box below and pass on any tips, points or facts we have wrong or have not covered.

We really like hearing from our readers, and hearing about which mods were the most effective for them, it helps us improve our recommendations and articles to reflect current trends in modifications and ensures that our guides and tips are kept up to date.

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