Tag: Tuning

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.

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June 18, 2021
AIR RIDE SUSPENSION GUIDE: ALL YOU NEED TO KNOW

So here it is: the, ahem, lowdown on everything air ride suspension has to offer… it’s time to get down.

It’s true to say that nothing has changed the show scene over the past decade quite as much as the availability of amazing air ride kits. But, while there are plenty of modern innovations, that’s not to say that the idea of air suspension is a new thing. Air ride systems have been around for about as long as cars themselves. Initially conceived to allow carrying heavy or uneven loads in relative comfort, there are examples as far back as the early 1900s. Various aftermarket kits have been on sale since the 1920s, and it became extremely popular with American bootleggers and whiskey trippers in the ‘30s and ‘40s for maintaining stock ride height with a boot full of moonshine.

Nowadays, of course, you’ll find OEM applications on everything from buses and HGVs to expensive SUVs and saloons. In short, air ride is far more common than you might think; it’s not some sort of underground dark art and, to be honest, it’s not particularly special either… until it comes to the world of modified car culture, of course.

But the question still remains, why should you look at air ride suspension as an option for your weapon of choice? Well, if you’ll excuse the pun, here’s the FC lowdown.

What is air ride suspension all about?

Air suspension is the only truly practical way of drastically changing your ride height on the go but, although many forum ‘experts’ will scoff, it comes with more benefits than simply being able to dump your car into the weeds. Yes, of course it makes your car look cool, there’s no denying that, but that doesn’t mean it has to come with a huge compromise on performance. Old skool hydraulic systems tend to offer a whole load of compromises but air? Well that’s a different animal. The best quality modern vehicle-specific kits are built with performance in mind and, in most cases, will not only offer better handling than standard, but very often they’ll boast greater tuneability than coilover or spring and damper set-ups too.

The truth is that, just like performance springs, modern airbags are progressive – the more they compress the stiffer they get – and this dynamic spring rate offers plenty of performance potential, especially combined with an optimal damper set-up. In fact, air ride was popular in drag racing and NASCAR as far back as the 1950s. There’s also plenty of race cars and drifters running air suspension right now, more than you may think.

When it comes to tuneability, with air suspension the ride can be firm and tight, soft and comfortable or anywhere in between. You can increase the pressure to firm up the ride for the circuit and then drive home in the lap of luxury, all at the push of a button. Then again you could just want to run your car super low but with the benefit of actually being able to get on your drive – a really novel concept we’re sure!

How does air ride suspension work?

There may be a few different configurations out there but the principle of how air ride works is always the same. Unlike ‘closed’ system hydraulic suspension, which uses a specific amount of fluid pumped (at extremely high pressure) from a sealed reservoir to rams on each corner, air suspension employs an ‘open’ system where air is used, expelled and replaced.

In a street-car system this cycle all centres around an air tank. The air is transferred via valves or solenoids to each airbag, lifting the vehicle as the pressure increases. The same air is expelled to the atmosphere when the time comes for lowering.

The idea is that a compressor will keep the tank topped up at all times, and the tank acts as a reservoir for the bags. Obviously, a bigger tank means more air in reserve for numerous rounds of lifting and lowering, while a larger compressor (or multiple compressors) will fill the tank to the optimum pressure faster.

Theoretically it is possible to run a system directly from a compressor, although it would take almost forever to ramp up enough pressure to raise the car. Some race cars and trucks have also been known to employ a type of closed system by doing away with everything bar the bags and using an externally mounted valve to fill them. On a road car, though, this isn’t exactly practical – after all, in-car adjustability is the whole point.

What components are needed for air ride suspension?

Airbags

An airbag, or to give it its proper name, an air spring, is just that – a simple pneumatic spring. Its job is to replace the standard coil, whether that’s in a coilover-damper configuration or a separate spring and damper set-up. Essentially this process is simply swapping out a coil for a spring that can be adjusted with air pressure.

There’s two common types of bag design – double convoluted bags and sleeves. The former, also known as bellows bags and donuts, are the most common these days and nearly always found used on the front suspension. These have a shorter stroke than sleeves but a superior load capacity and a more progressive spring rate. Tapered or rolling sleeve designs may turn up on the rear where clearance is an issue or if a higher lift is required. These are smaller in diameter than bellows bags and generally have a smaller load capacity.

Nowadays, all bags are designed specifically for liner travel and this means that they’ll expand and contract upwards and downwards rather than simply blow up like a balloon. They’re also suitably durable and contrary to popular belief they’re not at all easy to burst and will hold well over 100psi. On a road car that’s more than you’ll ever need.

Shocks

The big advantage of air ride systems over hydraulics is that standard handling can be improved or, at the very least, be retained. This has a lot to do with air being easily compressible to absorb bumps (unlike hydraulic fluid) but has even more to do with the system being able to retain a proper damping set-up.

All modern vehicle-specific air ride kits come with matched shock absorbers; many are supplied by well-known aftermarket manufacturers in the form of stripped-down coilover units. Some even have camber-adjustable top mounts and, as you’d expect, come with multi-stage adjustable damping and all the trimmings.

If it’s an older car you’re building, then there may be the rare occasion where a specific kit isn’t available. In most cases universal items can be adapted for your application relatively easily. Some universal kits will come with a range of dampers already installed, others will have bags with a simple provision (like a hole in the middle) to retain a shock absorber. The point is, with air ride you’ll always keep some sort of damper, and that’s obviously pretty vital for handling.

Tanks

The air tank is the business end of the operation – it’s the air supply to the bag on each corner. It’ll be no more complicated than the air tank on your average workshop compressor, though, albeit with a few more fittings. All you really need to know is which one to choose for your particular application.

In the old days, tanks were mostly made from steel and hidden away from view but now we tend to regard them as more of a showpiece. For this reason there’s also plenty of alloy items available in a number of bare, polished and painted finishes. Some are even skinned in carbon fibre or have all their welding polished out for a seamless look. Of course, it doesn’t hurt performance when all these are relatively lightweight too.

Generally speaking, air tanks are universal items and available in a range of sizes; this offers a trade-off between boot space and a system suited to repeated use. The more air in the tank, the more you can mess about with that ride height without waiting for a top-up. Some companies also offer tanks that are specifically designed to save space by fitting in a spare wheel well.

It’s worth remembering that every kit will come with a tank, some will offer a choice, but custom tanks are also getting more popular than ever. We’ve seen everything from adapted nitrous bottles, scuba tanks, fire extinguishers and even beer kegs. Anything that can safely hold air at high pressure could be a viable option.

Compressor

The simple job of keeping enough air in the tank is one that falls to a 12-volt compressor. Various sizes are available, and many people use more than one for rapid tank filling. After all, the faster the air is replaced, the more you can use your suspension. Compressors are inherently noisy too; another argument for using multiple units and keeping them running for an absolute minimum of time. At the very least you’ll want to take this into consideration when you’re looking for a place to mount yours.

Controlling how much pressure the compressor pumps into the tank is also crucial. On the more basic systems a pressure switch between the compressor and tank is used to cut power when the optimum psi is reached. Systems with digital management will often have the pressure switch incorporated into the manifold and a tank pressure display on the controller. In both cases, though, this will make refilling the tank to the desired pressure automatic.

Valves

The valves have the purpose of controlling the airflow from the tank to the bags and, in many cases, they also have the job of expelling the air upon lowering the car too.

The simplest manual systems come with paddle valves, which look like switches and are designed to be mounted within easy reach of the driver. On the back they’ll have a feed from the tank, an output for the relevant airbag and an exhaust port to dump the air. It’s a simple, reliable and cost effective set-up but one that does come with a few compromises.

Because the airlines need to go through the valves it requires running them into the cabin during instillation. If your tank is in the boot, for example, you’ll have a feed from the tank to the dash and then another back out to the rear bags. Due to the small diameter of the paddles, raising the vehicle can be a little slow too.

Solenoids

These are simply electrically operated valves and designed to eliminate the need for paddle valves in the cabin. They’re a little more expensive, of course, but enable the use of electrical switches, or switch boxes, and don’t require any airlines being routed inside the passenger compartment. In some configurations these are individually mounted directly to the air tank (that’s why you see some tanks with four threaded fittings in the front) and in other kits solenoids are supplied mounted-together in a manifold (or solenoid block) with an exhaust port and single tank feed. These make installation a far easier job.

Digital Manifolds and Management

To be honest, nowadays you’ll likely be wanting one of these. Designed not only to make instillation as easy as possible but to ensure day-to-day use is much more user-focused, digital management is fast becoming the norm, especially for daily-driven modified projects. Again, a digital management system will incorporate a manifold containing a collection of solenoids to control the airflow to each corner. But they’ll also be designed to work with a simple plug ‘n’ play wiring loom to take over management of the compressor functions and the power to the whole system. Many also include a handy feed for a second compressor and, although they’re all essentially universal systems, very often these are engineered so there’s only two or three wires that needed to be hooked up to the actual car. In other words, for DIY installations, they make life much easier – although that will inevitably come at a premium price.

Most professional installers will admit that home mechanics who can fit a set of coilovers and wire in an amplifier will have little trouble fitting a digital air ride kit.

Each system works around an electronic control module designed to add a whole host of extra features. These digital set-ups are on the cutting edge of functionality and allow trick touches like automatic levelling and adjustment, pressure monitoring, physical height monitoring (via height sensors), lift-on-start and emergency auto top-up.

Digital Controllers

Designed to work in conjunction with the management system, the controller negates the need to mount paddle valves or switches in your dash.

Some of the high-end management systems – like the 3H and 3P kits from Air Lift Performance – also employ Bluetooth so you can use your smartphone or tablet as a digital controller (via an app).

Perhaps the most important feature on digital controllers, not to mention the main reason why they’re so popular, is the ability to program a number of ride height pre-sets. This means you can reach the desired level either automatically on start up or at the touch of a button; something that definitely can’t be achieved with a paddle or simple solenoid-based system. Gauges

Pressure gauges are important in any budget paddle system to keep a check on what’s going on at each corner. These offer the only way of knowing the ride height without physically getting out and having a look… assuming, of course, you know the optimum pressure for each bag. Most air ride gauges offer a dual readout so it’s rare that you’ll need a separate item for each.

Height Sensors

The vast majority of air ride systems, including those with digital management, are based purely on monitoring and maintaining a pre-set pressure in each airbag. There are a few, however, that rely on electronic height sensors mounted to each corner of the chassis to automatically maintain a constant ride height no matter the load, distribution or amount of passengers. This is a well-established idea that works well in changing vehicle conditions, but the best next-generation systems can monitor both ride height and air pressure. The latest 3H Management kits from Air Lift Performance are designed for exactly that and use a complicated algorithm incorporating height and pressure information to keep the level constant at all times.

Airline and Fittings

The airlines have the job of connecting all the other components together, and most air ride kits include a good few meters made from commercial, DOT-approved plastic. Now, although no one likes to hear the word ‘plastic’ when it comes to holding their pride and joy up off the tarmac, it’s actually far safer than it sounds. After all, they’ve been using exactly the same stuff on HGVs for years – and that’s usually on the brakes!

Commonly available in 1/4-inch and 3/8-inch diameters, the thing to consider is that bigger lines equal faster inflation of the bags, but this may come at the cost of overshooting your target pressure more easily. Whatever size you use, all modern airlines are designed with simple instillation in mind. Kits will always include premium-quality, push-fit hardware making it a simple case of cutting the line to the correct length, and pushing each end into the fittings. That’s about it.

Hard Line Installs

For maximum flash at the local show ‘n’ shine, many prefer a ‘hard line’ install which, for the most part, is exactly what it says on the tin. What they don’t tend to shout about so loudly is that replacing some or all of your plastic lines with copper or stainless steel piping is easier than you might think. In fact, it’s not unlike making up a brake or clutch line and, provided they are the same diameter, they’ll even push into the same fittings. Simple.

Arguably hard airlines offer no real performance benefits because there’s no noticeable flex in the plastic airlines anyway. They’ll almost certainly require more fittings (with an increased risk of leaks around the joints) too, but there’s no denying they can make any boot install look amazing.

Air ride suspension configurations

2-Way and 4-Way systems

The first thing to consider is exactly what type of kit you’d like to go for. Nowadays 4-Way systems are by far the most popular and, as you’ve probably guessed, these allow for precise adjustment of each corner individually.

2-Way systems, in which the bags on each axle are hooked together, were popular in the past, particularly in the US, because of the ease of fitment and the fact you only need two valves or solenoids – one for the front and one for the rear. The downside is that we actually have corners and roundabouts here in Europe, and a 2-way system can magnify body roll in any bend because the loaded airbag on the inside will always try to transfer the air to its unloaded partner. To put it bluntly, 2-Way systems aren’t always the most practical in performance cars and everyday drivers… although if you’re building a quarter-mile-munching hot rod they could still be useful.

Basic 4-Way set-ups

Nowadays most cars go for a 4-way system. We’ve also talked about the fact that some systems incorporate digital management and others use valves or solenoids, but what’s important is that each configuration takes a different approach to installation.

It’s also good to remember that each of these set-ups can be adapted to your particular application with different size airlines and tanks, or the use of multiple tanks and compressors. In their very purest forms, though, there’s four basic ‘single-tank-single-compressor’ set-ups: manual (paddle valve), solenoid-controlled, digital-pressure and pressure/ride height-sensing digital management systems. Here’s what they look like…

Air ride suspension maintenance

Air suspension systems don’t require much more maintenance than a set of coilovers – just a quick check over once in a while to make sure nothing is rubbing, worn or broken. Despite what you might hear, leaks and split bags are extremely rare. A properly-installed kit should last a lifetime as long as you remember one little rule – moisture in the system is the enemy. Basically speaking, fluid getting into a digital manifold is bad news for your wallet and things will get even worse if that fluid freezes in the airlines – the worst case is that it’ll expand and split the plastic pipes.

The problem is that all compressors create moisture and it will often accumulate in the tank before being pushed around the whole system. Luckily all modern tanks should utilise a separate valve at the bottom, which should be periodically drained. It’s best to do this after ‘airing out’ your car and, in most cases, this will shed any fluid lurking in the system. Some kits also come with various water traps to be installed in between the compressor and tank or the tank and manifold.

Top contact: www.airliftperformance.com

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June 16, 2021
CLUTCH GUIDE: EVERYTHING YOU NEED TO KNOW

It’s rare to see a tuned car without an uprated clutch, so we spoke to Competition Clutch to find out why in our performance clutch guide.

The main purpose of an uprated clutch is to replace the standard item which can’t handle the level of torque the car is producing. It generally depends on the car and driver, as a hard used, but less powerful engine will wear its clutch out far faster than a more powerful engine driven gently. Clutch wear can be as extreme as slipping instantly under load, or it can occur when you use full power for short periods including drag racing, drifting, or during fast road use.

Standard clutches are designed so that even the least talented motorist can drive smoothly. But the payoff is a shorter life and inability to handle extra power. Many supercars for example struggle to launch hard more than a few times without destroying the clutch for this exact reason. But if the manufacturer had installed a clutch that could effectively handle the power under hard use, it would be too difficult for most owners to use.

Read on through our clutch guide and you’ll become an expert in the field!

What is a clutch and what does it do?

In simple terms, your clutch is the component that connects the engine to the transmission to drive the wheels. It works by using a friction disc (connected to the gearbox) that is pressed by a sprung pressure plate against a flywheel (which is connected to the engine) to transfer drive between the two. Disengaging the clutch, by pressing the clutch pedal, separates the friction discs and the flywheel, stopping that transfer, allowing the engine to continue turning without the connection to the wheels, this in turn allows you to change gear or stop altogether.

Clutch guide: Are they all the same basic design?

Most automotive clutches use the same principle of some form of spinning friction disc clamped to a flywheel by a pressure plate to transfer power, but the types of friction materials used, the size and design of the discs themselves and the number of friction discs used in any platform or application can vary. You start with an OE replacement clutch for non-modified vehicles. However, once you begin to increase power, you will need a clutch with stronger pressure plate and more aggressive and hard-wearing friction materials. These generally come in stages, such as 2, 3 and 4, and allow good street driveability. Next is multiplate clutches, which increases the torque capacity without the need to increase spring strength or clutch diameter. This uses multiple (usually two or three) clutch discs, with friction materials on both sides of each and makes for a lighter clutch pedal than an equally-strong single plate application. The final option is what is known as a ‘paddle’ clutch, which instead of the clutch plate being a circular disc, it is made up of a number of fiction ‘paddles’ or ‘pucks’. Known for their snatchy nature, but also an ability to hold high power without slipping, they commonly come in 3, 4 and 6 puck configurations.

What are clutches made of?

While the outer pressure plates are generally always a sprung metal design, the clutch discs themselves will use various friction materials depending on the application and power handling. Here are the most common materials and their qualities:

Organic

Smooth, durable (and usually quieter) and easy on the opposing mating surface, organic materials are common but suffer in high performance applications due to their intolerance to heat build-up and shorter lifespan.

Carbon/Kevlar

Similar clamping properties to organic materials with smooth operation, but able to withstand heat more vigourously when mated to a highly-rated pressure plate.

Ceramic

Offering the highest friction co-efficient, ceramic offers a lower necessity for high clamping force as the material provides more grip. The flipside is that ceramic materials wear the flywheel’s surface more quickly, sometimes causing shudder and a harsher feel. Mainly for competition use and applications where you are doubling or tripling your car’s stock output.

How do aftermarket clutches differ to OEM ones?

OEM clutch kits are designed to work with the factory power output of the vehicle and most will begin to fail if you substantially increase the power through tuning. Aftermarket clutches are available in different ratings to be able to work at much higher power and torque levels, meaning whatever your car’s power or driving style, there will be a clutch available to suit. Also, many aftermarket performance clutch options are lighter than stock clutches too (especially when combined with a lightweight flywheel) meaning less rotational mass for the engine to turn, equating to freer revving and lower transmission losses.

Why, or when, would you need to upgrade your clutch?

It is worthwhile upgrading your clutch if you are planning a considerable increase in power and torque – for example, boost increases, re-mapping and engine builds – as this will place more strain on the whole drivetrain and wear out a stock clutch more quickly. This is when you need a performance clutch.

The options available to you will depend on your level of power upgrade and intended usage.

How important is it to get the right clutch?

Aside from making sure you get a clutch that physically fits your car’s transmission, you also need to consider your car’s power and torque, plus your driving style and how you intend to use the car. While there is no point simply buying the strongest paddle clutch available if you are not going to have the power to warrant it, under specifying your clutch can lead to it wearing out prematurely and not being fit for purpose. Just bear in mind that for street driving, pedal weight and ease of modulation are also a concern if you want your car to drive well and be useable in traffic etc., whereas in racing conditions an aggressive, snatchy clutch is less of a problem as long as it can take the abuse.

Clutch guide: What causes clutches to fail?

Clutches are fairly durable, but heavy abuse or increases in power will mean they wear much more quickly and need replacing more often. If the clutch slips (doesn’t fully engage), the linkage could be out of adjustment, or the clutch disc could need replacing. You can tell if your clutch is slipping by flooring the pedal in a high gear at low revs and seeing if the revs rise without a corresponding increase in speed. If this is the case, your clutch is on its way out.

What other mods should you consider when uprating your clutch?

You should consider upgrading the flywheel, if it is available for the vehicle, and always replace the throw-out bearing and flywheel bolts when installing a new clutch. If you are upping the power considerably, you may also want to consider fitting a limited slip differential, uprated driveshafts or even an uprated gear-set.

Are there any downsides to uprated clutches?

With single-disc clutches, the ‘in traffic’ drivability tends to suffer if you move past organic and segmented ceramic setups and onto paddle clutch setups. This is because of the snatchy, all-or-nothing nature of high performance paddle clutches meaning useful clutch slip (to aid modulation when engaging) is all but non-existent. The solution to the downsides of a heavier paddle-style clutch are solved by using a multi-plate organic clutch such as the MPC from Competition Clutch. They have the same power holding capabilities as a racing twin-disc clutch, but the ‘in traffic’ drivability of a Stage 2 street clutch.

Other than ensuring you get the right clutch for your application, what are the most important things to look out for when buying uprated clutch?

Look for a reputable brand (such as Competition Clutch) that you know or have seen in many magazine articles and that is used on race cars and enjoyed by fellow enthusiasts across the globe. That way you know you will have great customer service and back-up should you have any problems. As far as price is concerned, you really do get what you pay for, and that unbranded Ebay-special may end up costing you a lot more in the long run if it fails to live up to expectations. We’d also recommended a professional installation because clutch installs (especially the alignment) can be more a difficult job than you may think. The right tools really make all the difference in the world.

Clutch guide: What makes up a clutch?

A clutch is fairly simple with three main components in a single plate example. It basically consists of two surfaces; one connected to the engine and one connected to the gearbox, and a central friction disc that transmits torque between the two.

Flywheel

This is the part that is bolted to the crankshaft of the engine and therefore spins at engine speed at all times. With the clutch engaged, the flywheel friction plate and the clutch plate are pressed together, sending torque from the flywheel to the gearbox. Different weights of flywheel are available, and although these are mostly used for other performance reasons, a lighter flywheel will also have an increased clamping effect. We’ll explain the effects of flywheel weight later on in this feature.

Clutch plate

This is the part connected to the gearbox. When the clutch is engaged the clutch plate is pushed against the flywheel to transmit power between them. There are various materials and styles of clutch plate friction pads depending on the use of the car and the torque the clutch is expected to transmit, and this will be talked about in a separate section.

Clutch cover

This is the part that pushes the clutch plate on to the flywheel when you engage the clutch. It has sprung metal fingers arranged in a circular fashion facing inwards that give the clamping force that helps stop the clutch plate and flywheel from slipping. An uprated clutch usually has an uprated cover which increases the clamping force of the clutch cover fingers. The downside of more clamping force is a stiffer clutch pedal, which can range from slightly stiffer to something barely useable on the road.

Paddle clutches

The majority of uprated clutches are actually what is known as a paddle clutch. A paddle clutch, rather than having 360 degrees of friction material like a standard clutch, is segmented into sections, usually four or six, but other combinations are available. These are commonly known as a four/six paddle clutch, or sometimes four/six puck in the USA. The reason for this segmented design is to help with heat dissipation. With increased power you are more likely to overheat the clutch, potentially warping it or simply ruining the friction material. Making it less effective.

Sprung plate or not?

Almost all uprated clutch plates for road cars, even ones intended for enormous power levels, are ‘sprung’. This means they have springs between the centre plate and the friction pads to dampen the shock load as the clutch is engaged. This makes driving it on the road, where the clutch is constantly being engaged and disengaged, much smoother than without springs. On race cars smooth clutch operation isn’t so important so these are generally unsprung to give the most positive action possible, less weight, and less potential failure points.

Multi-plate clutches

Multi-plate clutches are commonplace these days on uned cars. They have more than one clutch plate with metal plates sandwiched between them. Using multiple plates spreads the load and increases heat dissipation, giving increased grip for the overall diameter of the clutch. This means a twin plate using friction materials that are more road-friendly can handle similar levels of torque to a single plate race-only sintered clutch for example. In race cars they use multi-plate clutches to save weight and rotating mass by using the smallest diameter clutch possible with a huge number of plates. Conversely, cars with very large diameter clutches as standard, V8s for example, tend to not need multi-plate clutches until a much higher power level than most four cylinder engines with smaller clutch diameters.

Flywheel weight

There’s a lot of talk about the effects of a lightweight flywheel, but to put it simply, on a high performance car there are many benefits. The first thing to remember is as it’s a rotating mass you are not simply removing 5kg. The effect is magnified by the speed of rotation and the gear ratios, meaning it can be the equivalent of a 150kg weight saving in a low gear, though in high gears it can be less than 10%. From a performance point of view it is why cars tend to rev faster and more freely with a lighter flywheel, especially in lower gears and of course out of gear. From a clutch point of view this lighter rotating mass makes it easier for the clutch plate to grip it, further increasing the clutches’ performance.

As ever with tuning, there is a downside, and that is a slight drop in drivability due to this decreased clutch mass as the revs drop more easily, making it harder to drive smoothly and easier to stall. Sometimes a slightly higher idle speed is used to stop a car with a very light flywheel from stalling when the clutch is disengaged.

Hydraulic or cable operated clutch?

The vast majority of cars these days come with a hydraulically operated clutch. But there are still many popular cars with a cable clutch, Cosworths and Mk2 Golf GTIs for example, and this can cause problems when going for a high performance clutch. In a similar way to brakes without servo assistance need to be pushed harder to operate, a clutch with cable operation is much harder to use than the equivalent clutch with hydraulic assistance. With organic clutches and standard covers it isn’t an issue, but once the cover is stiffer you need a strong leg to operate the clutch. And once the plate material is uprated you need extra care to pull off smoothly. Single plate clutches can just about be driven on a cable clutch, but anything more will need a hydraulic clutch conversion to maintain any hope of road drivability.

Source

June 8, 2021