The modified car scene has changed. Unless you’re a particularly skilled mechanic, it’s unlikely you’ll be able to pop the bonnet on a modern vehicle and perform the kind of DIY tune-ups that formed the culture decades ago. If tinkering is your thing, then you’re likely going to need a car that’s at least 15 years old.
Equally, the UK’s craze for garish customisation that reached its zenith in the 1990s has nosedived since the turn of the century. The trend still exists in niche circles, but the days when you had to go out of your way to find an unmolested Citroën Saxo are long gone, but the same cannot be said of current Citroën C1s.
Tuning cars doesn’t have to be like that, though. If anything, the scene has grown up, and the modification industry for diesel cars specifically has graduated largely to simple and subtle electronic upgrades that deliver more power, torque and even economy. It still pays to know what you’re doing, as grey areas such as insurance, warranties and just working out what to do and where to get it done need investigating. Our guide covers all you need to know when it comes to tuning a modern diesel car.
The easiest, most affordable and most abundant way of modifying a diesel-engined vehicle is a remap. Formerly known as chipping or chip tuning, remapping alters the software on the vehicle’s ECU (engine control unit). The ECU is essentially a small computer that governs the engine, so tweaking or rewriting its software is a simple and straightforward way of freeing up more power, torque and/or economy. The amount of power or torque you get depends on the remap, but there are plenty of options and specialists available, and the beauty of them is that they can easily be reversed so the car returns to its standard settings.
The majority of remaps don’t require any kind of fettling under the bonnet. They’re usually done via the OBD (on-board diagnostics) port, so it’s just a case of plugging in a laptop, or tablet, and allowing the update to run its course.
This process is bread and butter for the aftermarket tuning industry, but it’s also used extensively by car manufacturers. The vast majority of OEMs (Original Equipment Manufacturers) produce cars with one engine available in numerous different power outputs, such as the Volkswagen Group’s commonly found 2.0-litre TDI unit, which is sold in numerous different guises, and in cars across the Volkswagen, Audi, SEAT and Skoda ranges. A 148bhp 2.0-litre TDI engine in a Volkswagen Golf is virtually identical to the 118bhp version, which is in turn like the 181bhp version – the software has simply been mapped to deliver the appropriate levels of power and torque.
Tuning boxes work in a similar fashion to remaps, but they’re physical installations rather than software upgrades. Ultimately, they perform the same function – they’re plugged into the car’s electrical system and sync up with the ECU to deliver more power, torque and potentially better economy and emissions. They can be installed professionally or on a DIY basis.
Modifying for economy
Tuning, particularly remapping, is widely regarded as being a way to get more power, torque and to go faster. That isn’t necessarily the end game though, as diesel engines can be remapped to improve fuel economy and reduce emissions. The gains vary depending on the exact nature of the remap, but as an example, the fleet arm of telecoms giant BT remapped its entire 24,000-strong fleet of Openreach utility vans for the purposes of cutting emissions and saving fuel. It claimed the move, which was completed in 2013, improved economy by 11 per cent and reduced CO2 emissions by 20 per cent.
Economy remaps are gaining ground with fleets, as it’s a practical way for a company with a number of vehicles and a big annual fuel bill to save money, but there’s no reason why the same principles can’t be applied to individuals. Often, a remap for torque and power comes with a slight increase in economy anyway, the gains coming from the improved engine torque that allows you to pull a higher, and more economical, gear at any given speed. Even so, it doesn’t harm shopping around for the best blend or power and economy.
If your car isn’t running as it should, and feels like it is down on power, then don’t think that tuning it will magically resolve any issues. Most tuning firms worth their salt will refuse to touch it anyway, and any repairer will be able to diagnose the fault by plugging it into a fault finder, or coming up with a resolution after taking the car for a decent run.
But before running up any expensive garage bills, try buying a decent fuel additive, like Millers Diesel Power Ecomax, Exocet’s Diesel Supreme, or Wynn’s Formula Gold diesel treatment, and give the car a double dose. Take the car for a decent work out over a few days to see if there is an improvement in performance. Avoid supermarket fuel, and make sure that you only fill up with branded, higher quality fuels.
The cardinal rule is that the insurance company needs to know if a vehicle has been modified in any way. And if the kind of work that deviates from the manufacturer’s specification is kept under the radar, then the policy could well be void. Have an accident and chances are the insurer won’t pay out – and it could get worse if another party makes a claim against you.
Scare stories aside, if you’re up front you’ve got nothing to fear, and the price hikes might not be as awful as you think. The assumption is that insurers charge sky high premiums for any kind of modification, and in many cases they do, but the reaction depends just as much on the insurer as it does the type and level of tuning. A stripped out track car tuned to the hilt will require specialist and expensive insurance, but a mild, economy-orientated remap may not incur any premium at all from certain insurers, while others might stipulate a cap on the increase in power in line with a set fee, or no rise at all. Plenty of insurers specialise in cover for modified cars, so they’re worth a look. If you’re just planning a light remap, then it may be worth arranging it around the time your insurance is due for renewal, so you can price up standard policies and choose the cheapest one that accounts for the changes you have made to the car, post tuning.
Modifications come at a price, and it’s not limited to the cost of the upgrade. They can have an impact on residual values and it’s rarely positive. According to Rupert Pontin, head of valuations at used car pricing specialist Glass’s, engine modifications “have a significant impact on both value and desirability. Despite the fact that there are a significant number of reputable companies that carry out this work, there is still a deep misunderstanding of the impact on both performance and longevity of an engine subjected to different untested loads. Insurance companies load the premiums and the trade as a whole will stay clear of this type of car as a direct result. Only extremely high performance models offered through the trade, with full declaration of its modifications draw higher values, and to do so full details of the changes made must be carefully detailed”.
Rupert warns; “the problem is that, in many instances, it is not possible for a used car buyer, and subsequently the retailer, to tell what may or may not have been done to the car. If it is found before the car is sold, there is usually a cost to return the car to the manufacturer’s specification. If it’s not caught and the car is sold and subsequently involved in an accident or inspection, the presence of an upgrade that has not been declared to the insurance company may negate the validity of the owner’s policy.”
What can go wrong?
Aside from the fears of higher insurance premiums and blunted second-hand values, the biggest modifying pitfalls are botches. There’s a long tradition of enthusiasts taking the DIY approach and putting their own stamp on a car, and there’s an equally established custom of getting it wrong. A quick scour online will reveal near endless amounts of cheap and cheerful modifying equipment and home remapping tools.
Cosmetic upgrades are less of an issue – a badly chosen spoiler might look awful and it won’t do your resale values much good, but it isn’t much of a safety issue providing it’s screwed in. Playing with more critical components such as engines, suspension and brakes without specialist knowledge is a recipe for disaster.
When basic remapping tools are advertised on eBay for less than £20, the temptation is there to save on costs and have a go yourself. That’s fine if tuning is your day job and you’re particularly proficient, but a new ECU is likely to cost a lot more than that if you get it wrong, so it’s important that it is left to the professionals.
If you’re going down the professional route for a remap, then make sure the company offers a warranty on the work. Any firm worth its salt usually will, but it’s worth checking beforehand. Also of note is that aftersales cover is likely to apply only to the software, so if any other problems arise that aren’t related to the remap itself, you’ll have a hard time proving the two are linked. It’s unlikely though, and reputable firms will no doubt do their best to help out if anything comes a cropper, but it makes it even more important to choose your tuner wisely. The companies that advertise in Diesel Car have been in business for a long time, have a great reputation, and should be your first port of call.
Warranties: where you stand
There’s a standard issue answer when it comes to modifying a car, which is that any work carried out on a vehicle that results in it deviating from the manufacturer’s settings and performance will invalidate the cover. You’ll get the same blanket answer from pretty much any car manufacturer or warranty provider. However, as with insurers, every company varies in terms of its policies, so there may be more leeway with certain manufacturers and warranty providers than others. A call to the car maker’s warranty department is worthwhile if your car is still covered by the factory and you plan to tune it. Likewise, companies that offer aftermarket cover may still be willing to do so if they are aware of any past or impending modifications beforehand. There’s no guarantee they’ll agree to it, and aftermarket providers are likely to charge an extra fee if they agree to cover, but you’ll never know if you don’t ask.
Some tuning companies claim that remaps do not appear on manufacturers’ diagnostic equipment, so it’s highly unlikely they’d ever be detected. That’s still breaking the rules as far as manufacturers and warranty providers are concerned though – and there’s no guarantee of a remap’s anonymity, so it’s best to play it safe and be up front and honest.
Manufacturer approved: modifications that donít void your warranty
Some car manufacturers offer their own in-house or factory approved enhancements, which are often worth a look. OEM-approved modifications are rare and they leave less scope for the kind of personalisation a lot of enthusiasts go in for, but they’re usually tasteful packages, developed by professionals, and make good cars better. The icing on the cake is that these modifications have the backing of the car maker, have been tested extensively, and so they don’t void the warranty.
Essex-based performance firm Mountune specialises in tuning Fords and although it doesn’t do diesels currently, the company does offer Ford-approved packages for Fiesta and Focus models with low capacity petrol engines, the likes of which you’ll find in Eco Car. The upgrades improve in-gear performance and the firm has a recommended insurance partner – Greenlight – that offers cover with no extra charge for the modifications.
Thorney Motorsport in Northamptonshire offers a similar service tuning modern Vauxhalls and claims to have an “unrivalled warranty”, while MINI also has a suite of accessories under its John Cooper Works performance banner that range from more aggressive body kits to what it calls a “Pro tuning kit and exhaust” to boost power. But Volvo is perhaps the most interesting, offering Polestar upgrades for its older five-cylinder D3, D4 and D5 engines, and available from Volvo main dealers.
What does it cost?
The cost of modifications is entirely dependent upon what you do and where you go, with companies specialising in remaps advising that the price fluctuates depending on the make and model of the vehicle. Every company is different, and again, it really does depend on your car and what you’re doing, but somewhere between £250 and £500 for a straightforward remap from a specialist isn’t unrealistic.
Manufacturer-approved package deals tend to be more costly, but they usually include additional components – such as upgraded intercooler and air filters – and you get to hang on to your warranty. As for other modifications, the sky really is the limit. Upgrading the likes of brakes, suspension, tyres and transmissions can easily run into four or five figures and beyond if you get serious.
Springs, bumps and stoppers
Remapping is the obvious, and the easiest, way to tune a diesel engine, but there’s more to modifying than just the powerplant under the bonnet:
Lowering and stiffening springs and shock absorbers can improve road-holding, aerodynamics and reduce body roll. A well applied, dropped and firmed up suspension system can really tighten a car’s handling, especially if it includes polyurethane bushes, which are more flexible and allow the suspension to move more freely. It’s easy to overdo it though, which can cause uneven tyre wear, bottoming out, and a rock solid ride, so tread carefully. A full laser alignment check and adjustment can also work wonders to how the car drives and feels.
Wheels and tyres
There’s almost no end to the amount of aftermarket alloy wheels on offer, and although they don’t exactly add much to performance (save for being lighter than steel wheels), they do look the part when chosen wisely. Manufacturers usually have a good eye for alloy wheel designs, so a look at the accessories brochure or pages of their website is a good way of giving inspiration. It’s also worth checking out second-hand OEM wheels on online auction sites like eBay, if you’re on a tight budget. But beware, larger wheels might look good, but they can ruin the ride quality.
A good quality set of tyres, with all four corners on the same brand and model of rubber, is arguably the best way to improve handling, not least grip. Wider tyres add more drag, but they are often stickier, so it’s a fine balancing act.
Bigger, lighter, grooved or drilled discs – or even carbon ceramic items if money is no object – are serious ways to improve stopping power. However, you only really need to investigate these extremes if you have enormously increased what the engine is capable of, or plan on hitting the track. Uprated brake pads designed for fast road use are superb cost-effective modifications, and the same goes for braided brake hoses, which deliver more feel through the middle pedal.
An upgraded induction kit or air filter is a really easy, cheap and beneficial modification. The exact figure depends on the kit and the vehicle, but it’s possible to pick one up for less than £100. A K&N air filter for a 2003 Vauxhall Astra, for example, will cost just £60 and is guaranteed for a million miles. They suck more cold air into the engine, which improves its breathing and you get a bit of extra power – anything from single figures and beyond. They can also improve fuel economy, and the engine should breathe more easily.