Tag: Guides

We take a closer look at one sure-fire way to improve an engine’s performance potential; cylinder head porting.

We know that a better flowing cylinder head will improve an engine’s power potential, and we’re familiar with the terms porting, gas-flowing, and big-valve head but what do they actually mean. How do they work? And why do they give the power gains they do?

To answer these questions and get an insight into the world of head tuning we take a closer look at the world of cylinder heads…

What does the cylinder head do?

The cylinder head is what allows the engine to breathe. It allows air/fuel mixture into the engine through one set of valves, then seals the cylinder when the valves are closed so the mixture can combust and produce power, before expelling unwanted exhaust gases through another set of valves.

Specialists and tuners often refer to the cylinder head as ‘the lungs of the engine’, as air is drawn in, used to create energy and then expelled out again. And sticking with our anatomical analogy, the best way to think of a standard head is as the lungs from someone who has been smoking for 50 years. The airways are restrictive and could be better. A ported head, then, is more like the lungs from a long-distance runner; much more efficient and much less restrictive to performance.

Another way to look at it is to think of the bottom end of the engine as a big pump (as essentially that’s what it is), and the cylinder head is what allows air in and out of that pump. Obviously the more usable air/fuel you can get in, and the more exhaust gases you can get out, the more power that pump will produce.

However, sadly it’s not just a simple case of bigger is better. The head modifications need to work with the rest of the engine spec; there’s no point having a massively ported head if the rest of the engine (including induction, fuelling and exhaust systems) is more restrictive than the ports in the head. However, if the engine has got a host of other goodies like lairy cams, bigger injectors, and so on, the standard ports in the head can quickly become the most restrictive part of the entire gas flow in and out of the engine, and will therefore respond really well to porting and machine work.

Head ports

The ports are the passages that the fuel and air mixture travel along to enter the cylinder bores and the exhaust gases use to escape from the engine. The majority of standard heads have lots of excess material in the ports due to the costs involved with fine tuning each individual head after the casting process. Major improvements can be made to the head here. When you place the inlet or exhaust manifold gaskets on a factory head, for example, you will see that there is usually a good 1-2mm of material before the ports and the manifolds line up. This material can be removed to enlarge the port to offer less restriction to the flow of gases.

But it’s not a simple case of making everything bigger. A good flowing head will have the ports as straight as possible too, so the gases flow as directly as they can. This means that on some heads most or even all of the material needs to be removed from one particular area to straighten up the flow path as much as possible. The smoother and more direct the port flow from the manifold to the valve, the lower the restriction to gas flow.

In addition, some cylinder heads have valve guides that protrude into the throat area of the port, causing further disruption to the airflow. This is one key area that cylinder head specialists concentrate on; either ‘bullet-nosing’ the guides, or machining them back flush with the rest of the port can make a huge difference to the airflow, and therefore performance potential of the head.

Obviously, larger ports will flow more gases than standard ports, but it is as much about the shape and the flow of the port as it is about the physical size.

Traditionally this porting has been done by hand, and is something of an art-form – not something we’d recommend you have a go at yourself in your shed.

But modern-day technology does mean that specialists can use computers to help them out a bit. The first port and first set of inlet and exhaust valves are still ported manually (that’s where the art of porting comes in), but rather than worrying about multiple ports to deal with, they concentrate all their efforts on just one. This process can take several weeks; porting, testing, flowing, porting again, and so on until they are happy they have the best possible design. Once happy, the port can then be digitally scanned before the programme is loaded into a state-of-the-art CNC machine. The incredible accuracy of the CNC machine ensures that all ports are exactly the same shape and design, and therefore will flow exactly the same amount of air.

Combustion chamber

The combustion chamber is where the fuel and air mixture is ignited via the spark plug to cause combustion, and therefore energy. The more complete the combustion, in terms of burning all the available fuel and air mixture, the more efficient the engine will be and the more power it will produce.

The head doesn’t have an effect on how complete the combustion will be. Complex issues with the ignition and fuel timing through the ECU control that, but the combustion chamber itself can be smoothed and polished to make it less susceptible to coke build-up. And that coke build-up can cause hot spots within the combustion chamber, which in-turn can have an effect on how the fuel and air mixture combusts.

That’s why many specialists smooth out the surface of the combustion chamber at the same time as porting the cylinder head.

Cylinder head porting: Valves

The inlet and exhaust valves open to let fuel and air in, shut to create a seal in the cylinder, then open to let exhaust gases out.

Fitting bigger valves means the openings through which the air and fuel mixture enters, and exhaust gases exit, the cylinder are bigger. The bigger the opening the more gas can flow through. Simple as that, then?

Not quite. It’s not all about the size. Bigger valves have a lower gas speed entering the cylinder, which can cause problems with performance. Instead, specialists will work out how much air flow is needed to create the desired power levels, and then try to achieve this flow rate with as small a valve as possible, which in-turn helps to keep the gas speed as high as possible.

Typical ‘big valves’ in most applications are between 1-2mm larger diameter than standard, as this is the usual limit a valve seat in an alloy head will allow. With cast iron heads like the older Pinto engines, the valve seat is machined as part of the head so you can fit much larger valves without too many problems.

There are two types of valve; one and two-piece. Most OE valves are of a two-piece design where the head and stem are made from separate materials then fused together to become one. The easiest way to tell if a valve is a two-piece item is to put a magnet to it; two-piece valves have a magnetic stem and a non-magnetic head. One-piece valves are usually made of a high-grade stainless steel such as 214N.

On turbocharged engines, which can experience higher cylinder temperatures, the valves may be sodium-filled to help with heat dissipation.

The shape and design of the valve also has a huge effect on the way the head flows air/fuel mixture and exhaust gases. Some high-performance engines respond well to what are affectionately known as ‘penny-on-a-stick’ valves, so called because of how they look. They have a narrower throat to the valve, and the valve itself is flatter and thinner than standard. The area gained by removing material from the valve allows the gases to flow quicker and easier past the valve. However, it depends largely on the design of the port as to whether these valves will work or not.

Valve guides

The valve guides support the valve within the head. Most modern alloy heads have separate valve guides, but with the older engines, such as the Pinto and the Crossflow, the valve guides are actually part of the casting.

With alloy heads the valve guide is a separate piece because the head is too soft to withstand the opening and closing motion of the valve, meaning they would wear out rapidly. A steel guide insert is usually fitted.

With some performance engines such as the Cosworth YB, and many later engines, bronze valve guides are fitted as standard as bronze helps with heat dissipation. The valves, especially exhaust valves, get very hot and can expand, and the effect is even worse in turbocharged engines. The clearance between the valves and the guides is incredibly tight, typically between 1.5 and 2thou, so there isn’t much room for the valves to expand before they touch the guides. Bronze guides can deal with the heat better and help reduce the problem. They also wear much better than cast iron guides, and will last longer.

Valve springs

The valve springs’ job is to shut the valves after the camshaft has opened them, and keep them shut until the camshaft opens them again. In theory it is straightforward but there is a bit of science involved when choosing the springs to match the camshaft.

On a camshaft with high lift the opening and closing ramps on the lobes are usually quite steep and aggressive. As you can imagine, when the engine’s revving at 7000rpm the force at which the valve hits the seat as it closes is quite hard, and it is likely to want to bounce back off the seat a little. This is where uprated valve springs matched to the camshaft are needed, as they will keep the valve shut and eliminate this problem.

Also the valve springs have to be matched for height to avoid becoming coil-bound at full valve lift. A higher-lift cam will compress the spring more than a normal lift cam, so the valve spring will need to accommodate this. A valve spring should always have 40thou clearance between the coils when at full lift.

Double valve springs are also available for high-performance engines and work in the same way as single springs. The main benefit of double springs is they offer more strength to keep the valve closed, and it is not always possible to achieve this strength with a single spring. The second, inner spring, is always shorter than the outer spring. This means the valve is easier to open because there is less resistance at first, but when it closes it has the force of both springs pressing against it. This also helps keep the valve shut in engines with particularly aggressive camshaft designs.

Valve seats

The valve seat is what creates the seal when the valves are closed. Without an airtight seal the engine would have no compression and would therefore not run.

The part of the seat that creates the seal is the 45-degree angle that matches the 45-degree angle on the valve, and the thickness of this angle can affect a head’s performance. Narrower valve seats are less obstructive to the airflow, therefore a head with narrower seats is capable of producing more power.

The valve seat on the exhaust side helps dissipate heat from the exhaust valves. The exhaust valve seat needs to be significantly larger than the inlet seat because when the valve is shut, the contact between the two helps take heat away from the hot exhaust valve. If the contact area’s too small the exhaust valves would get too hot.

A lot of head specialists like to cut three angles in to the valve seats. The benefit means the seat is opened up to encourage the air/fuel mix and exhaust gases to flow around the valve rather than straight in at a 45-degree angle and potentially cause turbulence. Usually the first angle is cut at 60-degrees, the second angle is the sealing section at 45-degrees to match the valve, and the third is opened up to 25- or 30- degrees.

A valve seat is around 6mm thick, so the angles are typically divided up so that the first angle is about 3.5mm, the second is 1.5mm and the third is 1mm wide.

On high-performance engines specialists will sometimes cut five angles in the valve seat, or even cut ‘radius’ valve seats which further encourage the gases to flow around the valves.

Camshafts

The choice of camshafts is a world of its own, and is far too complex to go into detail here. You can check out our camshaft guide here.

However, the camshaft does have a massive influence on how the head works and reacts with different aspects of head tuning, so it’s worth summarising some of the key points while looking at cylinder heads too.

The camshaft turns rotational movement into linear movement to open and close the valves. The length of time the valves are open for (duration) and the height the valves are opened to (lift) are all determined by the camshaft design. These different designs will give an engine different characteristics, but as far as the head is concerned the camshaft dictates how much air/fuel mixture gets in and how much exhaust gases get out of an engine. Any modification carried out to the head, such as porting or bigger valves, needs a camshaft tailored to suit. For the best advice speak to cylinder head specialists or direct to the camshaft manufacturers, as they will be able to guide you specifically for your engine.

Camshaft followers

The choice of camshafts is a world of its own, and is far too complex to go into detail here. Which is why we covered it in its own feature back in the September 2017 issue (386).

However, the camshaft does have a massive influence on how the head works and reacts with different aspects of head tuning, so it’s worth summarising some of the key points while looking at cylinder heads too.

The camshaft turns rotational movement into linear movement to open and close the valves. The length of time the valves are open for (duration) and the height the valves are opened to (lift) are all determined by the camshaft design. These different designs will give an engine different characteristics, but as far as the head is concerned the camshaft dictates how much air/fuel mixture gets in and how much exhaust gases get out of an engine. Any modification carried out to the head, such as porting or bigger valves, needs a camshaft tailored to suit. For the best advice speak to cylinder head specialists or direct to the camshaft manufacturers, as they will be able to guide you specifically for your engine.

Cylinder head porting: N/A and forced induction differences

When porting the head of a turbocharged or supercharged engine, a different approach needs to be taken to that when porting a naturally-aspirated cylinder head.  With a turbocharged engine you can force a lot of air/fuel mixture through what is not necessarily a well-designed port, so the incoming gases are not too much of a problem. However, getting the exhaust gases out is.

On a traditional naturally-aspirated engine, the exhaust ports need to flow around 75% of the inlet ports. For example, if an inlet port flows 100cfm, the exhaust ports would need to flow around 75cfm. However, on a turbocharged engine the exhaust ports need to flow around 90% of the inlet ports. So, using our previous example, this would mean that the exhaust valves would need to flow 90cfm instead of 75cfm. Therefore, in short, a turbocharged head needs much more work on the exhaust ports, and a naturally-aspirated head needs more work on the inlet side of things.

Source

Having cemented god-like status in the car tuning community, the Toyota Supra Mk4 is about a strong a statement as you can make at a car event. Here’s our quick-fire Supra buying and tuning guide.

With so much excitement and disappointment right now around the new A90 Supra, there’s been a natural resurgence in interest for the old A80/Mk4. Of course, for people like us this enthusiasm never went away – we love these things, stock or modded, UKDM or JDM, subtle-and-smooth or big-power-and-boisterous, we’re well into a nineties Supra.

At launch, the Toyota Supra Mk4 offered a pair of fresh new engines: the 3.0-litre 2JZ-GE straight-six offered 220bhp, while the twin-turbocharged 2JZ-GTE amped this up to 276bhp. For the export models, Toyota saw fit to pump up the adrenaline a little, adding bigger fuel injectors and smaller steel-wheeled turbos to produce a peak 326bhp – the holy grail for the UK buyer today is to find a genuine UK TT6; that is, a twin-turbo with a manual six-speed gearbox in full-fat UK spec. Not easy to achieve, but they do exist! (Giveaway details are that the UK models had a bonnet scoop and glass headlights instead of plastic).

In all markets, the turbo models had the option of the Getrag six-speeder while nat-asp cars made do with the W58 five-speed manual – although the GT nature of the car means that a lot of them were bought with four-speed automatic transmissions, which does rather dull the fun.

Turbos got 17-inch wheels while nat-asps had sixteens, and with either engine you could option a targa Aerotop. The SZ-R, available from 1994, had the option of bigger 4-pot brakes, as did the RZ from 1995 – this was also the year that Recaro seats arrived on the option list. A mild facelift in 1996 introduced Sport ABS and made dual airbags standard-equipment, along with revising gear ratios and equipping the RZ with an aluminium radiator. Turbo models from 1997 had VVT-I along with revised ‘REAS’ suspension, and automatics had Tiptronic gear selection added. The Aerotop was discontinued in 1999, and Supra production ended in July 2002.

Buyer Beware!

It’s pleasing to know that Supras are pretty bombproof. Just look out for age-related wear such as warping of the dash top, boot rubbers perishing, and yellowing of the headlights on JDM examples. Naturally, being a 1990s Japanese car, you need to check thoroughly for rust – as a rule, fresh imports are likely to be less rusty than older imports or UK cars. You should also be careful to check through the history, particularly as very few Supras on the market are factory-standard: if it’s been modified, ensure that it’s been done by competent people with quality parts. There was a time when you could pick up Supras for relative peanuts, and some have been ham-fistedly modded by people who saw The Fast and The Furious and thought ‘how hard can that be?’. And finally, keep in mind that imported cars will have a 112mph speed limiter – better to know that in advance, rather than embarrassingly headbutting into it at an inopportune moment. Oh, and of course the easiest way to spot a proper UK car is by its functional bonnet vent, glass headlights and headlamp washer ‘horns’.

Toyota Supra Mk4 Top 5 Mods

Exhaust – from £450 (backbox)

The 2JZ responds well to exhaust upgrades (particularly if you throw in a decat, and we reckon Supras only look proper with a huge drainpipe poking out the back! The Blitz Nur is popular.
blitz-uk.co.uk

Fuel Cut Defender – £116.40

An essential for modded turbo models, the FCD changes the airflow signal to the ECU to trick it into thinking it never sees more than 1 bar of boost, which is the point where the computer cuts the fuel supply as a safeguard. Speak to the guys at Turbosmart.
turbosmart.com

Single turbo – £various

If you’re chasing big power (and remember, the stock internals should be good for well over 500bhp), swapping to a big single turbo is always a strong option.
garagewhifbitz.co.uk

Intercooler – £349

A bigger front-mount intercooler is another must for turbo Supras – Japspeed are the experts here.
japspeed.co.uk

Brakes – From £1,099

The stock brakes are pretty damn good, but you’ll need them to be even better if you’re throwing more power in. K-Sport offer a great range.
ksport.co.uk

Source

Each month we quiz a specialist with 10 quickfire questions about a product to give you the knowledge you need to not only make the right decisions when it comes time to upgrade, but also to have the ammunition to impress your mates at your next meet. This month we speak to Pipercross to get the lowdown on the humble induction kit.

What is an induction kit and what does it do?

An induction kit usually refers to the components used to replace the standard air box and cold air feed to the engine. Pipercross specialises in performance intakes of which the main function is to improve a vehicles performance, by improving its ability to feed cold fresh air to where the car needs it most.

Are induction kits all the same?

There are many different types of aftermarket performance air intake systems available.  Whilst the aim of all the intake systems should be the same (to increase the air flow the engine), the designs and final results can be very different.

What are they made of?

The two main components of an induction system are the airbox and air filter. The airbox provides a housing for the air filter and is used to channel cool air from outside the engine bay directly to the filter.  It also has the added function of isolating the air from the effects of heat generated by the engine.

An air filter is essential to ensure that air drawn into the engine is clean and free from any contaminants that would potentially be harmful to an engine.  There are many different shapes and sizes of filters used, dependant on the application (road car, desert rally car etc).  It is common for most OEM manufacturers to use pleated paper panel filters in the induction system while aftermarket performance products tend to feature a cone or cylindrical shaped filter to increase the available surface area.  The shape, size and material of the filter has an impact on the amount of air that is able to pass through it. Pipercross manufactures reticulated foam filters which are each hand made.

How do aftermarket induction kits differ to OEM intakes?

Usually they are larger and capable of flowing more air. Production cars are made up of a series of compromises, so they are able to deal with harsh environments and bad fuel. Where these are not factors, and people have the desire to remap and gain more power, the cold air intake will give the car the air it needs to cope with the extra fuel a remap will require.

Why, or when, would you need to upgrade your induction kit?

In engine performance tuning, a method of increasing a vehicle’s engine performance is to increase the fuel used in the combustion process.  This increase in fuel leads to an increased requirement of air to maintain the necessary air/fuel ratio. In some cases, the restriction posed by a vehicle’s standard intake system can limit the flow of air, hence the need for a performance induction kit.

How important is it to get the right type of induction kit?

There are several options when deciding what induction modification to make to a vehicle. There are three main categories: First up, a panel filter upgrade, which uses the vehicle’s existing airbox and replaces the standard pleated paper filter with high-flow filter made from cotton gauze, synthetic material or foam. Pipercross uses a unique foam system, which uses various thicknesses of finer or coarser foams, meaning these factors can be varied for different applications. Next is an open induction system, which removes the standard airbox and replaces it with a filter connected to the intake pipe mounted within the engine bay. As no airbox is used the air is drawn from within the bay where the air is warmer and less dense, so optimum performance may not be achieved. The use of a heat shield is often employed to segregate the filter element from the engine. In the case of Pipercross’s performance intakes for instance, the filter and pipework can been routed low down behind the front bumper to ensure that the filter receives cold air despite not being housed in an airbox. The final option is closed cold air intake, where a performance airbox is designed around the optimum sized filter for the performance gain required.  Housing a filter in an airbox provides a constant flow of cool air to the filter, whilst shielding the filter from the high engine temperatures.

What are the limitations of OEM intakes? Do aftermarket induction kits suffer the same fate?

Compromise. The limitations of the OEM intakes are often due to the regulations that are imposed on the car manufacturers. A lot of the restrictions in the standard airboxes are due to the need to remove noise from the induction system, which often disrupts airflow. The OEM induction systems are designed to do a specific job to a specific power output. What the designers didn’t have in mind was when the cars are tuned and need to flow more air. This is where the Pipercross kits take over.

What other mods should you consider when uprating your induction kit?

Just like many other aspects of your car, its induction system will work at its best when the rest of the car’s breathing is optimised. This means it is essential to ensure that every element of the engine’s breathing system is also uprated to be freer flowing, from intercoolers, to pipework, throttle bodies, manifolds, exhaust system and even the head ports. Things like an uprated turbo, if applicable, would also be worthwhile, as would an ECU remap and possible fueling upgrades to match with the increase in airflow.

Are there any downsides to aftermarket induction kits?

When an aftermarket induction system is fitted it removes the restriction of air flowing to the engine.  Due to this aftermarket intakes can be considerably louder than the standard one fitted to the vehicle.  For the majority of people this is part of the allure of an induction kit, however some people may find this a nuisance. Also, some open induction systems, without the correct ducting to ensure a strong cold air feed, can actually end up losing power due to drawing in the hotter, less dense air from the engine bay.

Other than ensuring you get the right one for your application, what are the most important things to look out for when buying an induction kit?

Always look for a trusted brand with experience in all forms of motorsport, as the development path taken by these large teams eventually ‘filters’ down to road car applications. You should also consider the purpose of what you want the car to do. Street cruiser, trackday warrior, will noise be an issue? Consider warranties too, an established company with a good reputation will be far easier to deal with should you encounter any issues. Your engine bay is exposed to heat cycles daily, add in the worst the weather can throw at it and a component may fail. It’s then you want a company like Pipercross who will help you when you need it most.

Source