Honda L15 Tuning

"All you need to know about performance parts and tuning the Honda L15 engine!"

The Honda L15 are popular engines and with carefully picked performance mods like remapping, turbo upgrades and camshafts you will noticeably improve your driving pleasure.

Let us look into L15 tuning and summarise the optimum modifications.

"Franken builds" are popular with heads, and cranks from other L series engines being swapped to create a higher capacity engine. The VTEC heads and turbo models are generally the highly sought after items.

History, Power & Specs of the L15 Engine

The L15 is the most popular L series engine on our site and we should note that the L15B7 and the turbo L series engines make for fantastic project cars, L15BF, L15B7, L15B9, L15BE, L15BE and the L15BG. All engines respond well to tuning, but you'll get a lot more power for your money from the turbo units.

L15 engine

  • L15A (i-VTEC / CNG)
  • L15A2 i-DSI
  • L15A1 VTEC
  • L15A7
  • L15B1
  • L15B DOHC VTC Turbo
  • L15BF VTC Turbo
  • L15B7 VTC Turbo
  • L15B9 VTC Turbo
  • L15BE VTC Turbo
  • L15BE VTEC Turbo
  • L15BG VTEC Turbo
  • L15BU
  • L15C VTC Turbo
  • L15Z1 i-VTEC
  • L15Z5/2 i-VTEC
  • L15Z6 i-VTEC

The L15 was fitted to the following models

  • 2002 1.5 L L15A (Fit/Fit Aria/Airwave/Mobilio)
  • 2013 1.5 L L15B DOHC (Fit)
  • 2016/2017 Honda Jade RS
  • 2016– Honda Civic turbo
  • 2017– Honda Civic Si
  • 2018– Honda HR-V
  • Honda CR-V
  • 2018– Honda Accord
  •  Honda Mobilio
  • Honda City
  • Honda BR-V
  • Honda Civic Hybrid

Tuning the Honda L15 and best L15 performance parts.

Best L15BF, L15B7, L15B9, L15BE, L15BE & L15BG upgrades

Just because particular parts are popular with L15 owners it doesn't mean it is good, instead we will concentrate on the ultimate parts that will give your L15 the best power gain for you spend.

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 torque gains are on offer for cam upgrades.

Fast road cams normally push up the bhp and torque through the rpm range, you may lose a little low end power but your higher rpm power will be higher.

Motorsport and race cams, push up the higher rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.

In a typical daily driver must carefully try to optimize your bhp range to your cars usage.

You will never find a L15 Motorsport cam is a pleasure to live with when driving around busy urban areas. This is because a competition cam causes a very lumpy idle, and makes the car more prone to stall or jerk along in stop start traffic, sadly though many ignore this and end up ruining a perfectly good car and having to revert back to a fast road, or OEM cam profile.

Different L15 engines respond better to less aggressive cam durations than others.

The engine timing and fuel pump and injectors also have an effect 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.

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

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

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

The L15 power plant respond well to upgrades and we're pleased to see that there is a growing number of mods and tuning parts around.

Mapping allows a tuner to to establish the full potential of all the modifications you've done to your L15.

(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 NASP engines, but figures achieved may differs on the modifications you've applied and the condition of your engine.

It is the main goal to any performance tuning project to feed air and fuel into the L15 engine

Headers carry the air from the filter and allow it to be drawn into the engine and mixed with fuel.

The bore size, shape and rate of flow of the Intake headers can make a big effect on to fuel engine efficiency on the L15.

Commonly we find the intake headers are crying out for aftermarket tuning parts, although a few makers provide fairly well optimized intake headers.

Increasing the L15 valve size, doing a bit of L15 port enlargement and head flowing will also raise power, this will make space for an improved power increase on other mods.

L15 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 L15

All engines respond well to tuning, but you'll get a lot more power for your money from the turbo units. So swapping in an L15B7, L15BF, L15B7, L15B9, L15BE, L15BE and the L15BG is a fairly easy route to getting a turbo in your project.

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

If an engine is fitted with a turbocharger (L15BF, L15B7, L15B9, L15BE, L15BE and the L15BG) then modifications are simpler to install and you will discover turbocharged engines use better components as standard.

There are common areas of failure for every engine, with some being over specified and some just sufficiently able to handle stock power. Discover these limitations and upgrade to forged components to handle the power.

There are many people spending a fortune on turbocharger upgrades on the L15 only to watch the motor catastrophically fail when it's first rolling road session.

Bigger capacity turbos often suffer low end lag, and little turbos spool up quickly but don't have the peak end engines power gains.

Over the last 20 years the choice of turbochargers is always developing and we are seeing variable vane turbochargers, allowing the vane profile is altered according to speed to lower lag and increase top end torque.

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

It is not unusual that there is a limit in the air flow sensor AFM/MAP on the L15 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 was restricting torque at a much lower level.

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


When you increase the performance you will need to pay attention to to the fuel system.

More performance needs more fuel. It makes sense to be generous with your flow rate on the injectors.

The accepted safe increase is to add 20% to the flow rate when buying an injector, this allows for injector deterioration and allows you 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.

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

4 Cylinder NASP engines

  • 58 PSI 285cc/min 200hp
  • 58 PSI 426cc/min 300hp

4 Cylinder supercharged engines

  • 58 PSI 312cc/min 200hp
  • 58 PSI 468cc/min 300hp

L15 Performance Exhausts

You may need to improve your exhaust if your current exhaust is actually creating a restriction in flow.

On most factory exhausts you'll find your 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.

Don't go with the largest exhaust you can buy you'll slow up 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.

Common exhaust restrictions can be located the catalyst and filters installed, so adding a freer 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 L15

The L15 engines are generally reliable and solid units, as long as you follow the manufacturers service schedules, and use a good quality oilthey 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.

Regular oil changes are vital on the L15, especially when tuned and will help extend the life and reliability of the engine.

If you would like to know more, or just get some friendly advice on Tuning your L15 engine please join us in our car forums where you can discuss L15 tuning options in more detail with our L15 owners. It would also be worth reading our unbiased Honda tuning articles to get insights into each modification and how effective they will be for your car.

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 modifications work best for them on each model of car. Your feedback and comments are used to keep this page up to date, and help improve the accuracy of these L15 articles which are continually updated.

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