Subaru Legacy Tuning

"All you need to know about tuning and the best Subaru Legacy Mods!"

The Legacy and the finest tuning mods for it come up often in the emails and queries we get and we were recently asked for suggestions of the best mods for a Subaru Legacy in our forums, so we've put this tuning guide together and will be adding to it in the near future.

The choice of mods and upgrades for your Legacy is quite impressive, but what is the best way to tune a Legacy? Do all performance parts and upgrades work well on this model?

Accordingly, we've compiled this essay to go through the key areas you should tweak and to highlight the finest adjustments we think you should make.

Competing with the Accord 626 and Stanza, the Legacy needed to be quite a special car. It certainly ticked this box, especially considering the fact that it has run from 1989 to 2020 and sold over 4 million models. The outback offered raised suspension and more family practicality.

The Subaru Legacy are awesome to work on and with carefully picked motorsport enhancements like a remap, turbo improvements and camshafts you will dramatically maximise your driving fun.

Let us examine the options for your Legacy tuning and show the best modifications.

History of the Legacy Engine

First generation (BC/BF/BJ; 1989)

  • BC for 89–94 Sedan BF for 89–94 Wagon (raised roof) BJ for 89–94 Wagon
  • EJ22T

Second generation (BD/BG/BK; 1993)

  • BD for  Sedan BG=Step-roof Wagon (Raised Roof) BK for Standard-roof Wagon
  •  EJ25D
  •  Twin sequential turbocharged EJ20H

Third generation (BE/BH; 1998)

  • BE for sedan and BH for wagons.
  • 2.5 L EJ251 Engine standard.
  • 2001 EZ30, & 3.0 L H6

Fourth generation (BL/BP; 2003)

  • BL for sedan models and BP for wagons
  • EJ255 , EJ20X and EJ20Y
  • Subaru EE flat-4 diesel
  • IHI VF38 twin scroll turbo was replaced with later models receiving a VF44 (auto) or VF45 (manual) turbo.

Fifth generation (BM/BR; 2009)

  • EJ25 2.5 L flat-4 engine and the EJ20
  • Legacy B4 2.5GT tS STi JDM 2010.

Sixth generation (BN/BS; 2014)

  • BN Sedan  BS for Wagons
  • FB25 and a 3.6-liter flat-six EZ36D

Seventh generation (BW/BT; 2020) 

FB25  FA24

Best Legacy parts

Tuning the Subaru Legacy and finding the best Legacy performance parts.

When talking about the best modifications for your Legacy engine, we are going to concentrate on the parts that offer the biggest return for your cash.

Tuning tips and articles
Please watch our video which covers the 5 principles of tuning your Legacy. Be sure to keep up with our latest YouTube content and subscribe.

Best mods for your Legacy

  • Air Induction kits and Exhaust Upgrades - Please be warned on their own these mods won't ADD TORQUE for most setups, but they can help release power after other modifications by minimizing the restriction.
  • Lightened Flywheels - a lower mass flywheel will noticeably improve the engines free revving nature. Not always beneficial for all Legacy engines.
  • Braking Mods - Stopping your Legacy needs to be near the top of your Mods list.
  • Upgrades to turbochargers and superchargers - Adding a turbocharger is the most dramatic method to increase your intakes air supply, ensuring you are able to use more fuel and make better power figures. It is one of the most costly modifications you'll see massive gains.
  • Upgraded Camshafts are one of the most significant mechanical changes, but should always be setup by someone understands performance engines and it is often hard to find a suitable cam near you but you might have a local firm to regrind a stock camshaft .
  • 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.
  • Legacy Handling modifications - Tweaking your suspension dramatically improves Legacy handling Adjustable coilovers and better bushings are what is needed here.
  • ECU Tunes - A Remapped Legacy ECU gives the most advantage for the money, replacement ECUs, and inline Tuning boxes are all alternatives.

Legacy Tuning Stages

Typical stage 1 mods often include: Drilled & smoothed airbox, Intake manifolds, Performance Brake Pads, Suspension (mild drop), New Bushes, Remaps/piggy back ECU.

Typical stage 2 mods often include: Fast road cam, Ported and polished head, high flow fuel injectors, Brake Discs (drilled/slotted or grooved, fuel pump upgrades, induction kit.

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

Legacy Handling/Suspension Upgrades

Adjusting the handling is often the first step in using the Legacy.Adjusting the Legacy's handling is often the first step in tuning it.

One of the most popular reasons for tweaking your Legacy suspension is to improve its handling. In spite of this, we regularly witness the same mistakes over and over again.

Coilovers permit you to adjust the suspension height and this allows you to setup your cornering performance.

Is there anything I should keep in mind while deciding on suspension mods for my Legacy?

Improvements to the bushings

Bushing upgrades are needed, so what's involved?

It is possible to connect the Legacy's suspension components to the chassis of the Legacy using poly bushes, which are drop-in replacements for the rubber mounts. The rubber ones usually start to fail with time and need replacing anyway, so why not upgrade.

New OEM rubber bushes may have a major impact on the performance of your vehicle.

Because the polyurethane bushes are firmer, the ride may be a bit rougher, but they will last longer and maintain the handling.

Increased vibration and play may also quicken the decay in other suspension components.

A new set of poly bushes will assist in mitigating the excessive play associated with rubber bushes.

Some poly bushings are hard to locate, but most will find the primary mounts readily available in their regions You may be able to have custom poly bushes created to suit your needs.

How low should you go on the Legacy?

According to data gathered and analysed by TorqueCars, the optimal suspension drop for most street-legal vehicles is from 28 millimetres to 43 millimetres, while the optimal suspension drop for vehicles already equipped with reduced springs is 20 millimetres.

These tolerances may be drastically reduced if the wheel size is changed. Even with 16 or 17-inch wheels and conventional suspension, lowering the vehicle may create a  slew of new issues.

Legacy Camshaft Upgrades

Sporty camshaft profiles helps you to boost higher RPM power so are more suited to petrol engines, than diesel ones. We've always seen peak power hikes through performance camshafts on most engines. So altering your Legacy camshaft will make a difference to the engine bhp. Choosing a higher performance camshaft profile raises the power range accordingly.

Fast road camshafts usually bump the bhp throughout the rpm band, you could drop a little low down bhp but the high end rpm power will improve.

Motorsport and race camshafts, bump the high end rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.

A Competition cam won't do well if driving around busy urban areas.

You should ideally optimize your engines power to your preferences so for a car driven daily stick with a fast road Legacy cam

Each engine responds differently primarily due to the airflow when cams are fitted depending on the cam being more extreme cam durations so view each engine and camshaft as unique due to manufacturing tolerances and quality variations so set your engine up on a rolling road.

The engine timing and fuelling and fuel pump also will say much on the power gains you'll achieve.

A longer valve duration can adjust the power range, and on most engines there are some advantages to extending the intake or exhaust durations and valve lift.

The Legacy power trains respond well to upgrades and we see that there is a growing number of upgrades and tuning parts around.

ECU Mapping Improvements for the Legacy

Mapping helps unlock the full potential of all the upgrades you've fitted to your Legacy.

(Sometimes engine tuning/remapping the ECU is not an option, so an aftermarket ECU is the route to take, and most of these exceed the specs and performance of your factory ECU's but ensure it has knock protection and that you get it setup properly.) It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NA (naturally aspirated) engines, but the outcome will depend much on the upgrades you've done and the condition of your engine.

Air Flow improvements on the Legacy

Tuning an engine for maximum performance involves increasing the amount of air and fuel going into each cylinder.

Air is sent from the filter to the intake manifold during the suck phase, and then it is sucked into the engine cylinders together with the gasoline during the squish phase.

The Legacy's fuel mixing and power may benefit greatly from adjustments to the Intake manifolds' shape and flow rate.

Although some automakers do provide acceptable intake systems, most inlet manifolds beg for racing components.

Performance can also be boosted by installing big valve kits, expanding the Legacy ports, and performing some head flowing. This has the amazing side effect of increasing the possibility for even more performance gains in other areas.

Legacy 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 Legacy

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.

When your car is fitted with a turbo parts are simpler to install and most turbocharged engines are built with many forged and stronger components.

There are weak spots for every engine, with some being over specified and some only just able to handle stock power. Discover these limitations and install better pistons and crank to utilize the power.

It's not unheard of drivers spending a stack of money on turbo charger upgrades on the Legacy only to have the engine go up in smoke soon after it's used on the roads.

Large upgraded turbo units tend to experience a bottom end lag, and small turbo units spool up quickly but don't have the high rpm engines power gains.

In the last 10 years the choice of turbos is always moving on and we commonly find variable vane turbos, allowing the vane profile is altered according to speed to lower lag and increase top end power.

Twin scroll turbos divert the exhaust gases into a couple of channels and push these at differently angled vanes in the turbo. They also improve the scavenging effect of the engine.

It is common that there is a restriction in the air flow sensor AFM/MAF on the Legacy when loads more air is being pulled into the engine.

We note 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor limited performance at a much lower level.

Adding a supercharger or additional turbo will make large performance gains, although more challenging to install. We have this article on twincharging if you want to read more.

Legacy Fuelling Upgrades

When you boost the torque you will need to pay attention to to the fuel delivery.

More torque needs more fuel. Performance fuel pressure regulators can can improve throttle response.Most tuners we speak with say to over specify your flow rate on the injectors.

The accepted safe increase is to add 20% when fitting an injector, which takes into account injector deterioration and gives a little 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.

Legacy Performance Exhausts

Only look to boost your exhaust if the existing exhaust is actually creating a flow problem.

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

Do not go with the largest exhaust you can source 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 can be traced to the emissions filters installed, so adding a higher flowing race aftermarket one improves flow, and rather than doing an illegal cat removal, will keep the car road legal. We should explain that performance catalysts perform a similar power improvement to catless exhaust mod and have the added benefit of keeping your car street legal, as decat or catalyst removal is not a street legal modification.

Weak spots, Issues & problem areas on the Legacy

The Legacy engines are pretty solid and give little trouble 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 intake clean to remove carbon build up By avoiding short journeys where the engine doesn't warm up and using good quality fuel you can reduce this risk.

Frequent oil changes are vital on the Legacy, especially when tuned and will help ensure reliability of the engine.

If you want to know more, or just get feedback on Tuning your Legacy engine please join us in our friendly forum where you can discuss Legacy tuning options in more detail with our Legacy owners. It would also be worth reading our unbiased Subaru tuning articles to get insights into each modification and how effective they will be.

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

We love to hear what our users have got up to and which parts work best for them on each model of car. We use your comments and feedback to improve the accuracy of these Legacy tuning guides which get regular updates and revisions.

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

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