Tuning the BMW N18

We rely on our visitors to pass on tips and tell us about their projects and what worked on their car, and this article is the culmination of the feedback we have received. First let us look at the history and specs of this engine and then consider which tuning modifications work best on it.

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.

What are the most effective N18 modifications

When talking about the best best for your N18 engine, we are going to tuning mods that give the biggest return for your cash.

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

Fast road cams tend to boost the bhp and torque over the rpm band, you might lose a little bottom end bhp but the top end will be better.

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

On a daily driver should ideally to match your bhp range to your typical driving style.

I'd be shocked find a Competition camshaft is a pleasure to live with when driving in heavy traffic.

Each engine responds better to more aggressive camshaft durations so set your engine up on a rolling road.

The ECU mapping and fuel pump and injectors also will make differences on the bhp gains you'll get.

Longer valve durations 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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Modifying to Stage 1:

 Panel air filters, Remaps, Sports exhaust manifold, Intake headers, Fast road camshaft, .

Modifying to Stage 2:

 Fast road cam, Sports catalyst & performance exhaust, Ported and polished head, high flow fuel injectors, fuel pump upgrades, .

Modifying to Stage 3:

 Internal engine upgrades (pistons/head/valves), Competition cam, Twin charging conversions, Adding or Upgrading forced induction (turbo/supercharger), Engine balancing & blueprinting, .

ECU mapping should help to unlock the full potential of all the parts you've done to your N18.

It will usually give around 30% more power on turbocharged vehicles and 15% on NASP engines, but you mileage will vary depending on the parts you've done and the condition of your engine.

Shoving more fuel and air into your N18 is the whole point to any engine performance tuning project.

The intake plenum carries the air from the filter and allow it to be pulled into the engine cylinders.

The bore size, shape and rate of flow of the Plenum can make a substantial difference to to fuel delivery on the N18.

It's not uncommon that intake are needing a performance upgrade, although a few OEM provide reasonably well designed intake.

Fitting big valve kits, getting port matching and head flowing will also boost torque, & more importantly will allow you to get increasing the torque increase on other upgrades.

N18 turbo upgrades - which are best?

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

A stock N18's internals can reportedly cope with around 300-320bhp before it needs strengthening. As most are fitted to FWD there seems little point exceeding this anyway.

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

If the engine has forced induction tuning mods are giving better power gains and turbo engines are built with better components.

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

Discover these limits and upgrade to higher quality components to utilize the power.

It's not unheard of people spending a lot of money on turbo charger upgrades on the N18 only to watch the engine block explode on it's first outing after it's been enthusiastically driven.

Larger capacity turbos tend to suffer low end lag, and low capacity turbos spool up more quickly but don't have the peak end bhp gains.

Thankfully the choice of turbos is always evolving and we now see variable vane turbos, permitting the vane angle is altered according to speed to lower lag and increase top end torque.

Twin scroll turbos divert the exhaust gases into two channels and direct these at differently profiled vanes in the turbocharger. They also increase the scavenging effect of the engine.

You'll commonly see there's a limit in the air flow sensor MAP/MAF/AFM on these engines when a lot more air is being pulled into the engine.

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

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

Fuelling

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

More bhp and torque needs more fuel. Most tuners we speak with say to over specify your injectors flow rate.

The accepted safe increase is to add 20% to the flow rate when specifying an injector, helps cope with injector deterioration and allows a bit of spare capacity should the engine need more fuel.

N18 Exhaust

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

On most factory exhausts you'll find the exhaust flow rate quite well even on modest power gains, but when you start pushing up the power levels you will need to get a better flowing exhaust.

Please dont run with the widest exhaust you can find you'll reduce the exhaust flow rate - the best for power gains are usually between 1.5 to 2.5 inches. It is the shape and material more than the bore size.

Typically exhaust restrictions are in the catalyst installed, so adding a faster flowing performance alternative will help avoid this restriction.

Weakspots and problem areas on the N18

The N18 engines are generally reliable and solid as long as they are regularly serviced and maintained.

Regular oil changes are vital on the N18, especially when tuned and will help extend the life and reliability of the engine.

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

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.

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 mods work best for them on each model of car. Comments are used to improve the accuracy of these articles which are continually updated.

This article was written by Waynne Smith on TorqueCars, and I appreciate your feedback and suggestions. This entry was filed under BMW, Mini. You can leave a response below or join TorqueCars forum to discuss this article and car modification in detail with our members.

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