Tuning a diesel car doesn’t have to be expensive to reap significant rewards, as Andy Goodwin finds out.

For many of us, modifying cars is an itch thatís hard not to scratch. Knowing more power lurks under the bonnet, or that your car could handle, stop or even look better than it does from the factory will goad you on to pick up the phone and start spending. If you havenít chosen your next car yet, itís also a great time to consider the platform youíll be starting with. For maximum bang-for-your-buck, diesel models like the five weíve picked here are particularly well-suited to a light fettle.

While we arenít suggesting anything too extreme, the hatchbacks, coupÈ, SUV and pick-up weíve chosen all respond well to an ECU tune, giving the engine a useful boost in power and torque. Not only that, but they all have passionate owners forums, clubs and a vibrant tuning scene. Thatís important, because it means thereís lots of tuning advice and a wide array of parts available at competitive prices. While modifications can always affect a vehicleís warranty, avoiding oddballs means youíll be able to choose the most reputable tuners and products, many of which can be fitted and removed discreetly. 

BMW 420d

BMW has earned a long-standing reputation for engineering driverís cars with rear-wheel drive and perfect 50:50 weight distribution. Based on the 3 Series, the svelte 420d CoupÈ, Convertible and five-door Gran CoupÈ maintains this legacy and have stunning looks. BMW has also left lots of performance on the table, because a quick and affordable remap can increase engine power by around 50bhp, from 188bhp to 238bhp. Thatís enough to improve acceleration markedly, whether punching out of a corner or joining a fast-flowing motorway. 

The BMWís standard suspension setup has come in for some criticism, being rather stiff, particularly when larger wheels are fitted. For this reason, some owners have found that fitting aftermarket adjustable dampers with softer settings can improve the ride and handling. Another popular modification is the addition of a Quaife limited-slip differential, improving traction by spreading torque across the rear axle. With so much grunt on offer, it can make a real difference.

Unlike many mainstream brands, the BMW M Performance accessories catalogue also means owners can modify their cars with official factory parts, ranging from black spoilers and diffusers to side sills bearing blue and red stripes and the M Performance logo. Exhausts and hardware are also available, but youíll no doubt have to pay a premium for the kudos of branded parts.   

Ford Ranger 2.2 TDCi

The Ford Ranger is the UKís best-selling pick-up, with chunky styling and an aggressive front grille that gives it a flavour of the American Ford F-150. The engines in the Ranger are rather more European in flavour, though, with the top-selling 2.2-litre TDCi diesel unit only summoning 158bhp. Luckily itís ripe for development, with 200bhp available through ECU tuning alone, liberating a meaty 325lb ft of torque. 

Popular mechanical mods include spacers to widen the front and rear tracks, along with lift kits and new suspension to boost ground clearance. Chunky alloy wheels and all-terrain tyres with a heavy tread pattern give the Ranger a shot of attitude and improved off-road ability, but can be noisy on the motorway and increase fuel consumption markedly. 

Bodywork upgrades are big business too, from flared bolt-on wheelarches to running boards and new roll bars for the load bed. New front grilles and headlights are also popular amongst enthusiasts, with many aping the looks of the high-performance Ford F-150 Raptor. Now that the Ranger Raptor has been confirmed for UK consumption next year, expect genuine and replica Raptor parts to start being swapped onto standard Rangers.

Land Rover Discovery Sport TD4

The Discovery Sport is capable of carrying up to seven people over almost any terrain, yet with just 148bhp from the entry-level ëIngeniumí diesel engine, you might not get there particularly quickly. As Land Rover shys away from larger capacity diesel engines in the Discovery Sport to keep emissions down, it is fast becoming a popular candidate for ECU tuning, with the temptation of around an extra 50bhp after just a quick remap and approximatley £400 to pay. Power increases to 195bhp are possible, making it even faster than Land Roverís own 177bhp version for a lot less money.

Gerry McGovernís chunkily designed SUV also lends itself to exterior accessories, particularly if you think it looks slightly too ëschool runí as standard. Add a roof rack with a front-mounted LED light bar, chunky mud and snow tyres and possibly even a winch and suddenly the Freelander replacement looks like an extra from an action film. Thanks to a loyal fanbase for the British marque, thereís also a large and vocal community providing a wealth of online tuning information, as well as organising meets and off-roading clubs and events.

In addition to increasing performance, much of the tuning for the Discovery Sport is geared towards improving its off-road abilities, helping it keep going in rough and tough conditions. Improved torque of up to 325lb ft will equally help when pulling away with a heavy trailer on the back. 

Peugeot 208

We couldnít feature a tuning guide without one of the biggest names in diesel engines. Peugeot has been a leader in introducing technology like diesel particulate filters (DPF) and selective catalyst reduction (SCR) that help to remove harmful pollutants from the atmosphere. And while the firmís power outputs are generally quite modest from the factory, a few moments of magic at a tuning company and big improvements can be made.

For example, the BlueHDi 100 engine is quite modest at around 100bhp, but can be enhanced to a whopping 135bhp and a hefty 235lb ft of torque for around £300. Thatíll transform a humble 208 supermini into a potential GT-worrier, while still looking resolutely sober in terms of exterior appearance.

And because the engine range is a joint venture between the PSA Group and Ford, and utilised in a wide variety of models, including CitroÎn, DS Automobiles, Ford, Peugeot and Vauxhall, thereís plenty of opportunities to upgrade and modify them. Thereís also a substantial catalogue of bodystyling parts, uprated brakes and suspension upgrades, helping to ensure that a breathed-on 208 looks as good as it goes, as well as stopping just as quickly.

Volkswagen Golf GTD

If youíre planning on giving your car some extra zip on the road, it helps if it looks the part, too, and so weíre finishing off with one of the most popular performance diesels on the market. The Golf GTD already has an attractive body kit, uprated brakes, a sturdy clutch and figure-hugging tartan sports seats as standard. This leaves you to cherry pick the parts you do want to upgrade, and see the biggest benefits from them. With 181bhp on tap as standard, the GTDís 2.0-litre turbocharged diesel powerplant is already good for a 7.5 second 0-62mph acceleration time, but around £400 will see this tumble. Thatís roughly the cost of an ECU remap, increasing power to around 220bhp and torque to 330lb ft, with no visual changes to the car to highlight the upgrades to thieves.

Thanks to the Golfís huge global following, thereís a massive network of owners and tuners designing and trying out parts, so finding the most reputable and reliable upgrades is very easy. Handily, a lot of parts are also interchangeable between the GTI and GTD, such as big brake kits, chassis upgrades and bodywork. While the suspension is well-sorted from the factory, everything is available, from simple and cheap lowering springs to full racing specification coilovers with adjustable dampers.

If you choose the automatic version with a DSG twin-clutch gearbox, tuning companies can remap the gearbox as well as the engine. Benefits can include faster gearchanges, different shift patterns and the ability to disable automatic upshifts while in manual mode.