Tag: Guides

TOP 5 BMW V8 CARS YOU SHOULD BUY

With the rush to electric cars and hybridisation, we decided we’d pick out our top 5 BMW V8 cars you should buy.

The motoring world as we know it is changing – turbos are now the norm, manufacturers are downsizing engines and with the announcement that from 2035 there won’t be any more new internal combustion-powered cars on sale in the UK it feels like now is as good a time as any to celebrate the almighty V8, because this is an engine that is quickly being killed off. The V8 is something truly special and while it’s not always the most powerful engine option and certainly not the most economical, it always sounds amazing and delivers an old-school muscle car feel to any BMW that no other engine can match. If you’ve ever been tempted by something with a great V8 under the bonnet this is your lucky day – we’ve picked our top 5 BMW V8 cars to suit (just about) every budget and they’re all guaranteed to put a huge smile on your face.

Top 5 BMW V8 cars

BMW E38 740i

Engine: 4.0-litre M60B40/4.4-litre M62B44
Max power: 286hp
Max torque: 295/310/325lb ft

Why?

If you want to be a baller on a budget the E38 7 Series is where it’s at. It still looks money and is arguably a far more classy prospect than the E65 Seven that followed it. It’s one of those cars that needs almost nothing to look good and it’s great value for money when you’re hunting for a V8.

What to pay

While other older BMW V8 motors have seen prices rising steadily, the E38 is yet to have its moment in the sun and, as a result of that, you can pick one up for not too much money. £2000 will get you into a 740i with around 130k miles but if you can stretch to £4000 then you’re spoilt for choice. For that money, you can grab yourself an SE with under 100,000 miles and we found a couple of examples to choose from. We also saw a 180,000-mile Sport in Imola red up for £3450 and beautiful Individual facelift car with 122k for £4950.

Our pick

We’d love a Sport for the M paras and the slightly meatier styling as well as the improved seats, but we wouldn’t pay over the odds for one as the basic car captures the essence of the 7 Series experience perfectly, and with some mods you’ll be able to spice it up anyway.

The good

Every time you drive your 7 Series you will feel like you’ve made it. It’s comfy, sumptuous, built like a bank vault and so incredibly cosseting. This is the sort of classic luxury, refinement and ride quality that is timeless. Pull up somewhere in your Seven and you will always feel like a big deal.

The bad

The M60 suffers from the Nikasil bore-wear issue, while on the M62 you need to be aware of the chain tensioners and plastic guides, and also the cooling circuit on both, including the water pump. Fuel tanks rust and leak and if the charcoal canister/vent gets clogged it will lead to the fuel tank imploding. Rust isn’t too big of an issue, but check the bottoms of the doors and the metal sunroof panel. The suspension and bushes also take some punishment due to the car’s weight so expect to have to spend some money there. Inside expect some electrical issues like the pixels disappearing on the OBC display.

Modding potential

Not huge, but you don’t need a lot to make an E38 stand out. Drop it on air, add some deep-dish splits and you’re basically there; you can get the Alpina-look front spoiler that does a good job of enhancing the front end, you might want to add the facelift rear lights, and, naturally, we’d add an exhaust to enjoy that BMW V8 but, otherwise, the best builds keep it simple and let the car’s natural class shine through.

We say

For the money, the E38 7 Series is an exceptional buy and one of the cheapest ways into BMW V8 ownership. The third-gen Seven has aged incredibly well and still looks smart and sharp, delivers exceptional levels of comfort and refinement, and just a few mods will make it look absolutely awesome. Balling on a budget has never been easier.

BMW E31 840Ci

Engine: 4.0-litre M60B40/4.4-litre M62B44
Max power: 286hp
Max torque: 295/310lb ft

Why?

Up until very recently, there was only one 8 Series and the original is still a unique and special machine. It looks quite unlike anything else BMW has ever produced and still turns heads today, and will get you attention wherever you go. If you’re looking for a unique V8 experience, this is it.

What to pay

840s start from around £8000, which will get you an M60-powered model, while £9000 will get you a 4.4-litre Sport with around 130k on the clock. If you want a tidy Sport with under 100k on the clock then you’ll need to spend around £15,000.

Our pick

If we can stretch to it we’d go for an 840Ci Sport – the 4.4-litre M62 is the better and more reliable engine and the Sport looks that much sexier. There are a handful of manual cars out there but we wouldn’t bother holding out for one, the auto suits the character of the car
just fine.

The good

It’s got pop-up headlights, which are an instant win, and it’s also a pillarless design, which just ramps up the cool factor. It looks stunning and it’s an absolutely superb GT, comfy, wafty, able to effortlessly eat up miles and look cool while doing it. Also, you probably won’t see another one so the exclusivity is a big part of the appeal.

The bad

It’s heavy, it’s slow and it’s not entertaining to drive. If you’re looking for something fun, this isn’t it. The M60 suffers from the Nikasil bore-wear issue, while the M62 is sturdy but check for leaking rocker cover gasket and failing timing chain tensioners which can lead to the plastic timing chain guides breaking, which will leave you with a large bill. Expect a lot of electrical niggles at this age, the suspension setup is complicated with a lot of components and the weight really takes its toll on all those arms and bushes, and if you get one with EDC it’s going to break and will be expensive to repair. Age and mileage are this car’s greatest enemy and can land you with some serious bills.

Modding potential

Wheels and suspension options are decent, styling less so with the Sport pretty much the best-looking setup for this car, and you can supercharge the M62, while the M60 can be perked up with an eBay chip (old-school tuning). Don’t forget an exhaust as it’s easy to get it sounding glorious. Beyond that, there’s not really much on offer, but lowered on the right wheels an 8 Series will look a million dollars.

We say

Far from the last word in driving dynamics and capable of crippling your wallet and your bank account in one fell swoop, the 8 Series is, nevertheless, hugely charming and still a sexy-looking beast. If you want to stand out from the crowd in something a bit special and can stomach some potentially costly repairs, it’s definitely worth a look.

BMW E39 M5

Engine: 4.9-litre S62B50
Max power: 400hp
Max torque: 369lb ft

Why?

You can’t possibly have a V8 buying guide without including the OG V8 M machine, the E39 M5. A legend in its own lifetime, the E39 M5 remains an incredible car to this day and delivers the perfect blend of everyday comfort with monster performance and sublime handling.

What to pay

While M5 prices have been climbing steadily over the years not all examples have been affected and, as a result of this, the price range for cars is huge depending on age, mileage and condition. The absolute cheapest cars start at around £8000, and for this you can pick up a 170k-mile car, and we surprisingly found two facelift models at this price point. Head towards the £11,000-mark and you get a bit more choice, but mileages are still high at around 130-140k; £15,000 will get you something with under 100k on the clock and the very best low-mileage examples will set you back upwards
of £20,000.

Our pick

We’d forego fancy options and concentrate on getting the best car we can – BMW was pretty stingy with standard spec so you could really go nuts with the options when the M5 was new. But, to be honest, the sat nav is going to feel very old by now, and while things like Heritage leather and Extended leather are nice it’s not as if the M5 feels cheap and low-rent on the inside anyway, and besides, it’s really all about the driving experience.

The good

The S62 is a monster engine that delivers huge mid-range torque but also loves to rev, and it makes the M5 an awesome machine, and it’s still seriously fast even by today’s standards. Then you have that chassis, which manages to deliver the perfect blend of ride comfort and absolutely superb handling, and it makes the M5 feel superb on just about any road. The steering is faster than that of a standard E39 and offers more feel and the whole package is just absolutely sublime. The E39 M5 won every group test it was in back in the day – with good reason – and it has lost none of its sparkle today.

The bad

General stuff will be age- and mileage-related so expect failing pixels on the OBC display, the heater resistor playing up, and look out for rust, especially on the sills around the jacking points, around the fuel filler cap and along the boot lid edge. The various suspension components will also have taken a beating over the years so budget to have to replace arms and bushes. The S62 does suffer from several problems that you need to be aware of, the major one being rod bearings. These wear prematurely when owners don’t allow the engine oil to fully warm up before driving the car hard, and if they fail then you’re looking at a hefty bill for some substantial engine repairs, if not a new engine. The best thing to do is to drive the car slowly and gently, keeping the revs low until the oil temperature gets close to 100°C, but with no idea of how the car’s been driven it’s definitely worth getting the bearings changed as a precautionary measure, especially at high miles. The timing chain tensioners can fail, which in turn will damage the chain guides, and the VANOS can also be problematic but it can be rebuilt and isn’t too expensive to fix these days.

Modding potential

Huge and there’s an awful lot you can do to an M5. Styling options are limited, but there are splitters and diffusers you can add, and if you have a pre-facelift car it’s easy enough to fit the facelift front and rear lights. You have loads of suspension options with some excellent coilovers to suit all budgets, plenty of wheel options and big brake upgrades as well. In terms of performance, there are a few NA mods you can do, like fitting a set of free-flowing tubular exhaust manifolds, and the obligatory exhaust is, of course, a must, but if you want some real power then it’s all about supercharging. There are a few kits available, with the most affordable of these being the ESS VT1-560 kit at around £5000, with other options available from Evolve and RMS.

We say

Prices may have been rising but the E39 M5 remains an affordable proposition, especially for such an iconic machine. Delivering the perfect blend of handling and performance with those timeless good looks, it’s an awesome package and a real driver’s car that shouldn’t be too ruinous to run and offers plenty of modding options. A true M icon that remains every bit as desirable today as it was back in the day.

BMW E9x M3

Engine: 4.0-litre S65B40
Max power: 400hp
Max torque: 295lb ft

Why?

The first – and only – V8-powered M3, the E9x remains every bit as awesome today as it was when it was first launched back in 2007. It combines aggressive, muscular styling with a razor-sharp chassis and that magnificent S65 that revs like nothing else, making this an intoxicating performance machine.

What to pay

The E9x M3 is so cheap now that, if it falls within your budget, we can really think of no reason not to buy one and question why you’d bother looking at anything else. You can pick up an E92 M3 with under 100k on the clock for just £11,500, which is kind of crazy when you consider just how much car you’re getting for the money. That will get you an early manual example and as prices creep up past £12k you’ll find saloons appearing along with convertibles and all of them will have around 100k miles or less. DCT cars start from £13,000, while £13,500 will get you a facelift manual saloon and we spotted a couple of higher mileage LCI coupés and convertibles here as well, but realistically you’ll need to spend closer to £15,000 for a facelift convertible or saloon and closer to £17,000 for a facelift coupé. The various special and limited edition models, meanwhile, tend to sit nearer the £20,000-mark and above.

Our pick

Our personal preference would be the coupé as you get that carbon roof, we’d pick DCT over the manual gearbox as it really suits the S65 so well, while EDC is nice to have but not essential, especially if you’re looking to upgrade the suspension anyway. The Comp pack, with its M359 19s, lower suspension and tweaked EDC is tempting but, again, only if you’re not looking to mod the car much in these areas. The special editions, meanwhile, can be appealing if you like a certain colour or the trim, or just fancy something a little more individual, but they are a chunk more expensive than the regular models.

The good

The E9x M3 is an absolutely awesome machine to drive and it’s a car that’s guaranteed to put a smile on your face. The S65 is simply sensational and the way it revs all the way to 8300rpm, feeling the way the power just keeps on building, all overlaid by that howling V8 symphony is something truly special and this car is an event. It’s not too big, meaning it fits comfortably on B roads, but still has loads of space inside and is a genuinely usable everyday proposition. The chassis is sharp and the handling is exceptional, and this is a machine that can really deliver next-level driving thrills.

The bad

There’s really not too much to worry about on the E9x M3 in general. The main issues to be aware of are both engine-related; the first is rod bearing wear, similar to that on the S62 in the E39 M5. The cause is the same, owners thrashing the engine from cold before the oil is hot enough, and excessive wear will eventually lead you to spin a bearing which is obviously very bad news. As before, keep the revs low (2-3k rpm) and throttle inputs gentle before the oil gauge reaches around 100°C and if the bearings haven’t been changed budget to get them done (£1500) as a precautionary measure. There’s no set mileage at which they fail and the oil analysis tests you can do aren’t foolproof. The other issue is electronic throttle actuator failure, but they can be rebuilt for under £500 for the pair, which really isn’t bad at all. Other negatives are the small fuel tank which, combined with the thirsty S65, means a small range, and the engine does really need to be revved to get the most from it and can feel a little flat before it really gets going.

Modding potential

With a car as popular as the M3, it’s no surprise that the aftermarket is absolutely brimming with mods and there’s so much you can do. For styling, you can have anything and everything in carbon, from the smallest vents to a whole vented bonnet, there are splitters, side skirt extensions, diffusers, CSL boot lids, the works. There are loads of lowering springs to choose from as well as a lot of excellent coilover kits available for the car, some with electronic damping, and there are numerous big brake kits to choose from, meaning you’re fully sorted on the chassis front. As for power, NA tuning is a little limited, but a primary de-cat and remap to go with it can net you an additional 20-30hp, and PSDesigns’ awesome velocity stack kit not only looks and sounds incredible but will also get you around 475hp. If you want more then supercharging is the best option, with centrifugal kits available from infinitas, ESS and VF Engineering, and each company has something to suit most budgets, and around £6000 will get you around 600hp. There’s also the positive displacement supercharger kit available from Harrop; it’s a lot more expensive at around £10,000 but adds huge low-end torque along with impressive power gains.

We say

The S65 is a sensational engine and the E9x M3 is an absolutely spectacular all-round package. Problems are few so it won’t be too expensive to look after, there’s a near-limitless selection of mods to choose from and huge horsepower is easily attainable, and while the S65 does make you work for the power, that just makes it all the more satisfying when you really open it up. For the money, the E9x M3 is an absolute steal.

BMW F10 M5

Engine: 4.4-litre twin-turbo S63B44
Max power: 560hp
Max torque: 502lb ft

Why?

After the V10-powered E60 M5 we all wondered where BMW could take the M5 next and the answer to that question was back to a V8, but with a pair of turbos strapped to it, and the result was explosive. The S63 made an eye-watering 560hp with a monster 502lb ft of torque and fed all that through an M DCT seven-speed ‘box; this was the quickest M5 we’d ever seen and, in terms of performance and tuning potential, this V8 monster can’t be beaten.

What to pay

Back when it was new in 2012, the F10 M5 weighed in at a hefty £73,000 and easily broke the £80k-mark with some options on board, so be able to pick one up for less than a third of that eight years on is astonishing, but the market has far from bottomed out. The cheapest M5s we found are £18,000, which we appreciate is still a fair old chunk of money, but it’s £18k for an F10 M5! These have about 80k miles, which is pretty reasonable, but chuck another £2k on top of that and you can bag yourself a 50,000-mile example. Facelift cars are about £22,000, while Competition models are around £25,000.

Our pick

There’s no such thing as a bad F10 M5 and we’d be happy with whatever we bought. The LCI changes were minor and you can retrofit the later, smaller steering wheel so that’s no big deal. At £20k for an M5 you really can’t go wrong and while the Competition pack is tempting, if you’re planning on modding the additions it brings won’t be worth the extra £5000 to you. While the options list was extensive, there are only a few things we’d have on our wish list: extended leather is nice and makes the interior feel that bit more special, the 20s are definitely a must-have as the 19s look way too small, and we’d also try to find a car with the M Sport multi-function seats as they look and feel even better than the standard seats and offer more support and adjustment.

The good

The most impressive part of the F10 M5 package is without a doubt the performance because it is truly otherworldly. 560hp is a lot, and a 0-62 time of 4.3 seconds is not but on-paper figures really can’t convey how insanely fast this car is in the real world. Seriously, we can’t tell you how quick this car really is. Beyond the performance, you’ve got the extremely impressive handling, and you won’t believe how light on its feet the M5 feels. It’s a truly exceptional package on every level.

The bad

There’s actually very little to worry about on the F10 M5 and, apart from oil pump failures on early cars and a small number of owners experience engine problems, it’s been holding up extremely well so far, with owners proclaiming it the most reliable M5 yet. Some cars suffer from high oil consumption and there are occasional problems with injectors and airflow meters, but that’s about it, really. There were some air-con failure-based recalls for the F10 platform and some cars suffer from rattles around the B-pillars and door trims, but if that’s all you have to worry about we’d say you’ve ended up with a really good car. The only other downside is the F10 M5’s sheer size – yes, it handles exceptionally well and feels light on its feet, but it never feels small and never shrinks around you and this is a car that is definitely best suited to fast, open roads rather than twisting B roads.

Modding potential

Really huge and the F10 M5 might be the best-supported M5 yet when it comes to mods. Browse any BM tuning site and you will see countless options when it comes to splitters, skirt extensions and diffusers, so you’re covered there. You’re spoilt for choice as far as wheels are concerned and there’s a decent selection of suspension upgrades available too. Of course, it’s really all about performance with the F10 M5 and huge horsepower gains are so easy to get – just a tuning box or a map will get you an increase of around 100hp and if you pair that with a set of catless downpipes you’ll have around 700hp to enjoy. Beyond that you’ll need some uprated turbos – plus the supporting mods to go with them – at which point you’ll be hitting 800hp+ without your S63 even breaking a sweat.

We say

The most powerful car on our list and the most powerful M5, the F10 is a monumental machine and the fact that you can buy one for just £18,000 is incredible. Modding potential is vast, huge horsepower gains are incredibly easy to achieve, it’s proving reliable and it’s an astonishingly accomplished car all-round. If you want to go fast, this is the V8 to throw your money at and you will not be disappointed with an F10 M5 in your life.

From Performance BMW. Words: Elizabeth de Latour. Photos: Marcus Lundell, BMW, Rich Pearce, Patrik Karlsson, Matt Richardson, Matt Woods

Source

June 29, 2021
KEYLESS CAR ENTRY: WHAT YOU NEED TO KNOW

Fitted for modern convenience, the keyless car entry systems on many vehicles are open to abuse from would-be thieves. We take a look at Ford’s keyless car entry system to find out why, and how to protect against it…

When manufacturers introduced keyless car entry for convenience when entering and exiting a vehicle, they probably didn’t realise that car thieves would quickly adapt to the new technology as well. Sure enough, modern day thieves have become more sophisticated and are able to target particularly vulnerable cars and as a result. And Ford’s reputation of high-powered-but-easily-stolen vehicles continues well into the 21st century, having suffered plenty of negative publicity surrounding keyless car entry theft. But the truth is there are plenty of car manufacturers in the same boat, and it’s one of the main the reasons that vehicle theft has risen by nearly 50% in the last five years alone.

Keyless entry is susceptible to theft, but there are a few simple steps you can take to better protect your Ford

However, if you’re worried about becoming a victim there are things you can do to ensure your car is kept secure, and these range from being more cautious and adding extra deterrents to disabling a thief’s ability to access your car entirely. To better understand how and why these can work, first it’s important to understand how criminals are targeting and stealing cars this way. The method is known as ‘relay theft’ and the process is sadly very simple with the right tools to hand; a relay amplifier and relay transmitter. As the names suggest, these gadgets allow thieves to identify a car with the keyless entry feature parked outside of a house, usually on a driveway for instance. By simply manoeuvring the portable relay amplifier around the outside vicinity of the house, it can detect the car key inside if it’s nearby and boost the key’s signal to reach further. A second thief standing by the car with the relay transmitter in hand will then pick up this boosted signal and the car is then tricked into thinking the original keys are nearby and so the car is unlocked and the ignition can be activated, and the car driven away.

Using sophisticated signal relays, thieves can use the keyless entry technology to gain access to your car

How to keep your keyless car secure

The process is quick and quiet, which is why it occurs frequently. Car manufacturers are already looking at ways to tackle the problem, and Ford’s answer is refreshingly simple. The latest keyless entry fobs on new Fiestas and Focuses no longer permanently transmit a signal, but instead have an in-built motion sensor which puts the fob into ‘sleep mode’ if it hasn’t been moved for 40 seconds. This means that while it’s hanging in your key box it’s not transmitting a signal for any thieves to relay, but when you pick them up and walk to your car full functionality is restored.

However, this tech is only available on the latest cars (some previous models can be updated at Ford), so what that means for most of us is being smarter about where you keep the car keys – at the very least storing them away from the front of the house so that it will be harder for a relay amplifier to detect. Better still is to place the keys in something that will block the wireless signal from being transmitted at all, and whilst some owners report a simple metal container (with lid) can suffice, a more practical option is a Faraday pouch. There are a number of these on offer, but it’s important to know that not all of them are tested and guaranteed to work, so it’s best to test it on your own car, which is easy to do by simply placing the keys in the pouch and trying to unlock the car. If the car recognises the key, the pouch doesn’t work.

Jamie protected his own Focus RS with the Autowatch Ghost, and he rates it very highly

Another option is to add a secondary aftermarket immobiliser that works independently of the original keys. Traditionally these were activated with a simple additional key fob, but modern technology means clever systems like Autowatch’s Ghost can be hard-wired to work with the car’s original CAN-bus wiring. These systems don’t require any additional switches or fobs, so the interior of the car remains untouched, but the existing buttons (on the steering wheel, door switches, or similar) can be used to de-activate the immobiliser. A specific PIN can be set up using a unique sequence of buttons, and the ignition simply will not activate without this code – even with the actual key present, not just a boosted signal relay. Furthermore, these systems can work with Apps on your smartphone, and will only de-activate the immobiliser when the phone is in the car. However, this does mean that if someone steals your phone, or hi-jacks the car with your phone in it, the immobiliser security is compromised – many professionals suggest sticking with the manually-entered PIN code. These systems have proven to be very popular with high-value modern sports and luxury cars, and have proven very successful on cars like the Mk3 Focus RS.

Of course, then there’s always the good old-fashion physical deterrent too. While physical barriers such as steering wheel locks, wheel clamps and security posts, are by no means a guarantee against theft, the extra effort required to bypass them is often enough of a deterrent to ensure a thief chooses to target another car. Finally, a tracking device can be fitted but that will only improve the chances of finding the car and having it returned after it is stolen, which isn’t ideal for many.

The final fail-safe is to turn off the keyless entry system all together (which can be done at a dealer), but then you lose all the added benefits of the system in the first place.

Security issues are nothing new with a fast Ford, and as the technology of the cars progresses so too does that of the thieves. And while you’ll never make your car 100% ‘safe’ from theft, all you really need to do is make yours more difficult to steal than the next guy’s, and most thieves will target the easier option.

From Fast Ford magazine. Words: Simon Holmes

Source

June 22, 2021
TURBOCHARGER GUIDE: EVERYTHING YOU NEED TO KNOW

If you want big power you need forced induction and turbos rule the roost when it comes to big boost – here’s our complete turbocharger guide to help you understand how they work.

Guide first appeared in Performance BMW. Words: Gerry Speechley, Elizabeth de Latour Photos: Viktor Benyi, Patrik Karlsson, BMW

What is a turbocharger and how do turbos work?

The turbocharger is probably the best-known method of forced induction and we’re going to delve into the finer working details of the exhaust-driven turbo-supercharger.

The turbocharger is essentially a centrifugal compressor, almost identical to a centrifugal supercharger, but instead of being driven mechanically from the engine, usually by a belt, it uses the exhaust gas energy travelling out of the cylinder head, through the exhaust manifold, to drive a turbine directly connected to the shaft of the compressor.

It has been said that this is ‘free’ energy and that the turbocharger does not take any power from the engine to drive it but this is not an accurate statement. The turbine is effectively an exhaust restriction, slowing the exhaust flow by using the kinetic energy of the gas to drive the turbine. The larger the exhaust turbine, the less restrictive it becomes, but it also gets heavier and takes more energy to get it to accelerate (spool-up). A smaller turbine will have less mass, and accelerate faster, but will eventually become more and more restrictive, limiting the available top-end rpm flow and power. As we will discuss, this has a major effect on the suitability of any specific turbocharger against the intended use of the vehicle.

Who founded the turbocharger?

All hail the great man Alfred Büchi who invented the turbocharger and received a patent for his efforts in 1905. The technology was introduced into aircraft development way before it hit the automotive market. The first to use it in a production car were General Motors in 1962, while Porsche made turbos sexy by creating the now legendary 911 turbo in 1974. Turbos are now used widely in both tuning and economy vehicles.

Turbocharger guide: what turbo should I buy?

So how do we select the correct turbocharger for our application? Well, we need to consider several factors: the selection of the compressor, the turbine and how we are going to use the vehicle. Getting these factors wrong can make the car a complete disappointment with dreadful turbo lag and a very narrow, extremely peaky powerband. We also need to consider shielding nearby components from the glowing red-hot turbine housing(s), and managing an appropriate oil supply to and drain from the turbocharger. We also need to fabricate an exhaust manifold to mount the turbo, and an exhaust system of the appropriate size to remove the expelled exhaust gasses from the turbo, generally much larger in diameter than the original exhaust.

As with any centrifugal compressor, we need to examine the compressor maps for the correct selection of the compressor wheel and we need to calculate the airflow requirements of the engine. We can then plot this requirement on our compressor maps to find the most suitable compressor wheel that will operate in its highest efficiency island to reduce excessive charge temperature increases.

Turbo lag is the biggest bugbear of the turbocharged car and occurs where the throttle is opened, and there is a delay before there is any response from the turbo. This can be caused by using a turbine that is too large or an excessive turbine housing A/R (Area to Radius) ratio.

We then need to try and select the correct turbine wheel and housing for our engine. The turbine needs to be large enough to flow a large volume of exhaust gas without causing any significant restriction at peak rpm but this leads to a turbine that will be very heavy, requiring large exhaust flow to get it spinning fast enough to produce boost. However, this also has the downside of meaning this install may well be almost halfway up the rev range with absolutely no low rpm boost and dreadful turbo lag.

If we decide to opt for a much smaller turbine wheel, then it will spool up to speed, as much as 200,000rpm, much faster, enabling boost from much lower engine speeds, but can then effectively block the exhaust at high rpm, limiting power production and increasing fuel consumption. We, therefore, need to select a turbine somewhere in between the two so that, on a performance road car, we start to build boost around one-third of the maximum rpm of the engine and continue to do so up to the redline. We then need to consider the turbine A/R ratio we require for our selected turbine. The A/R ratio is the ratio of A (Area of the turbine housing inlet) to R (Radius of the centre of the turbine to the middle diameter of the turbine inlet). A small A/R ratio will give better low-speed boost whereas the higher A/R will flow better at high rpm. It is this combination where road car manufacturers tend to choose mid-range power and a conservative turbine/housing selection rather than an all-out power combination.

Twin turbos and more!

There are however ways of having your cake and eating it, and that is with the use of multiple turbochargers. The use of two (or more) turbochargers can give the advantages of both a single large and a single small turbo. The inertia of the multiple small turbine wheels, combined with the pulsing flow of a reduced cylinder count to each turbine, means boost will be produced early, and the additional flow capacity of them combined means less or no restriction at high rpm. When we get to larger V engines, eight, 10 or 12 cylinders, then twin, identical turbos, one on each bank, is the preferred combination whereas on smaller in-line engines a single turbo makes the installation far more practical with little requirement for
multiple turbos.

You also have sequential turbos, something which only BMW’s multi-turbo diesel engines utilise. The basic principle is that you have a small turbo that spools up quickly to deliver good low-end response and performance and a second larger turbo that takes over at higher rpm. On the M57 engine, BMW actually put the large turbo first in the setup, so air was already flowing through it to reach the small turbo and this was done so that the transition from small turbo to big turbo was much smoother. On the triple-turbo N57 in the M50d models, a small turbo operates at low revs, with a large turbo joining in the mid-range and then, finally, the second small turbo comes online at higher revs with all three working together, while the B57 uses an even more complicated quad turbo setup.

Another sequential turbo system we should mention is where we direct all the output from one compressor into the intake of the second compressor, known as compound turbocharging. While only really seen in racing, this can produce enormous levels of boost: consider that a single turbo can only produce around a 3:1 pressure ratio, so, let’s say three times atmospheric pressure or 3 bar (45 psi) of boost. If we now feed the second turbo with this 3 bar air pressure, and it then further adds a 3:1 pressure ratio, we can achieve around 105 psi boost!

What are twin-scroll turbos and how do they work?

Turbochargers respond better to a pulsed exhaust input, so when multiple cylinders combine into a single flow, this pulsing is smoothed and lost. This is where twin-scroll (BMW, for example, calls it TwinPower) housings and manifolds come in, which keep exhaust gasses from multiple cylinders separate from each other, retaining the pulsed exhaust input. The exhaust streams from the cylinders are grouped together in such a way that ensures the turbo receives these pulsed inputs. Twin-scroll setups offer quicker boost response, improve low-end performance and reduce fuel consumption, so you can see why manufacturers use twin-scroll setups in single-turbo applications.

Turbocharger guide: technology

There have been other developments in turbocharger design in an attempt to reduce the spool-up time and hence lag with the use of ceramic bearings instead of the more usual oil-filled plain bearing bushes, and of ceramic, lightweight turbine wheels. These are proven to decrease inertia by up to 40%, reducing lag by around 30% but are more fragile, allowing only around 1 bar boost before mechanical failure of the material occurs, although this is easily enough for most road applications.

Another successful design for anti-lag has been the adoption of VGT (Variable Geometry Turbochargers), VAT (Variable Area Turbines) and VNT (Variable Nozzle Turbines), where the actual geometry of the turbine is altered in use to change the effective way in which the turbine reacts. The Garrett VNT system uses multiple moving vanes in the turbine housing that, at low rpm, direct the exhaust to flow through a smaller passage to rapidly accelerate the turbine wheel to make it act like a small housing, but then with the vanes gradually opening as rpm rises to minimise exhaust flow restriction. These VNT turbos can reduce spool-up time by around half that of a similar-sized non-VNT unit. Another development is the twin-scroll swing flap turbocharger where a plate directs flow into a small A/R scroll at low rpm for faster spooling of the turbo, then opening a larger A/R scroll for higher rpm, or the alternative arrangement is a flap that blocks the flow from the secondary scroll to the turbine and then gradually opens it into the twin-scroll operation position. The VAT turbocharger from Garrett was another design, this time altering the area of the turbine inlet, reducing the area to increase the speed as it hits the turbine, accelerating it faster, then gradually opening as speed increases to increase flow.

What does a turbocharger wastegate do?

A wastegate controls boost by allowing exhaust gasses to bypass the turbine once the required boost pressure has been reached in order to maintain the desired level of boost. Let’s get one thing out of the way – wastegates don’t actually make any noise, there’s no such thing as wastegate chatter, a wastegate is literally a flap that opens to vent exhaust gasses, that’s it. If it’s making any sort of noise, like the old N54 turbo rattling wastegate problem, that’s not a good thing. The wastage is controlled by an actuator which physically opens the flap – there are mechanical ones which measure boost pressure directly from the turbo and, once the desired pressure has been reached, the air pressure itself forces the actuator to open the flap, and the more pressure there is the more the flap opens in order to regulate the boost pressure. Electronic ones, meanwhile, use a sensor to read the boost pressure and this then sends a signal to the wastegate actuator when it’s time to open the wastegate. On some setups the wastegate is actually normally open and only closes once it receives a signal from the vacuum pump to close it and allow the turbo to spool, but the basic principle is the same and it functions in the same way as a more traditional wastegate setup once the desired boost pressure has been achieved. Boost controllers, meanwhile, raise boost levels by modifying the amount of pressure that the actuator ‘sees’ before it opens, allowing the turbo itself to generate higher levels of boost before the wastegate is called upon to regulate it, but they can’t raise boost pressure beyond the specific maximum that a turbo is able to generate.

Wastegates can either be internal, that is built-into the turbo exhaust housing which is what you’ll find on a factory turbo, or external, where the wastegate is literally a separate physical item that has to be mounted to the turbo, and this is what most aftermarket turbos use. The downside of internal wastegates is that the exhaust gasses are dumped into the path of the exhaust gasses coming out of the turbine and this disrupts the flow, causing turbulence and back pressure, which is bad when you’re going for power. With an external wastegate, you can have these gasses re-enter the exhaust at any point you want, minimising turbulence and back pressure, or you can vent them directly to the atmosphere using a screamer pipe, so called for obvious reasons. External wastegates also make it easier to change the internal spring, allowing you to increase (or decrease) the amount of boost it can comfortably hold.

Turbocharger guide: Blow-off valves

Blow-off valves, commonly referred to as dump valves, also known as diverter valves are placed somewhere after the turbo and ahead of the throttle body and they give the compressed air somewhere to go when you come off the accelerator and the throttle shuts. Without a blow-off valve (BOV), all that air is now trapped and while the turbo is no longer under load it is still spinning, so the air that gets backed up against the throttle plate gets chopped up by the turbo and you get a fluttering sound (compressor surge). A blow-off valve is held closed while you’re accelerating and when you let off the throttle it opens and allows the air to escape – an atmospheric blow-off valve will make the various chirping, chuffing and sneezing noises associated with turbocharged cars, while a recirculating one doesn’t, simply recirculating the excess air until the throttle is opened again, the valve closes and the air can now pass through the throttle body and enter the intake manifold once more. If your engine uses a MAF then you shouldn’t use an atmospheric blow-off valve as air that your MAF has already accounted for will be being vented to atmosphere and your engine will end up running rich, but if your engine uses MAP (manifold absolute pressure) then the sensor measures air pressure at the intake manifold so venting before this won’t cause any problems.

Source

June 18, 2021