Camshafts: tuning’s forgotten fundamentals. Let your engine sing in the right rev range.

A bigger turbo, a better intercooler and a fresh tune. Familiar territory for anyone building a turbo engine. Keep winding up the boost as you chase that power target. If the horsepower won’t come willingly, a little more pressure should persuade it.

But at some point in a serious build, it’s worth stopping to think about the openings you’re trying to force all that air through.

Camshafts have a major influence on how an engine breathes and where in the rev range it does its best work. The right profile can deliver more usable torque and unlock power like pulling a sock out of the exhaust. Choose poorly, though, and your daily driver might only wake up properly once you’ve already reached your destination.

Performance cams are still very much a thing. Good ones, too:
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Why do camshafts change an engine’s character so much?

The camshaft controls valve movement. Its profile and timing determine when a valve opens, how long it stays open and how far it lifts. Together, the intake and exhaust valve events determine how efficiently the cylinder fills and how effectively the exhaust gases escape.

It’s not just about getting more air into the engine. That air needs to move, and it needs to move at the right time. Changing the cams can therefore affect throttle response, idle quality and the entire torque curve. The same engine can feel completely different, even when the difference in peak horsepower isn’t enormous.

In a turbo engine, the right cams can also change how the turbo spools and make power considerably easier to find.

Speed and driving enjoyment don’t live exclusively at the highest point on a dyno graph, either. If the engine pulls harder where you actually drive, and where the revs land after each gear change, that can be worth far more than a few extra horses a whisker before the rev limiter.

Turbo camshafts: can more boost fix everything?

Many modern turbo builds retain the factory cams. A tune and a turbo upgrade can take you a long way without much fuss, while changing camshafts requires more dismantling and a closer look at the whole setup. That’s understandable. Opening the valve cover isn’t quite the same Friday-night job as swapping an air filter.

Increasing boost can push more air into the cylinders with the stock cams, too. What it doesn’t do is change the physical cam profile. A well-chosen cam upgrade can deliver more power at the same boost pressure, leaving your mates wondering why your Stage 2 setup pulls like a Stage 4.

And just as we want air to enter the cylinder, we also need it to leave. This can work rather differently in naturally aspirated and turbocharged engines. Exhaust manifold pressure, for example, influences how much valve overlap is useful. If exhaust-side pressure is high relative to intake pressure, excessive overlap can send exhaust gases charging in the wrong direction.

Factory cams are often quite capable, particularly in performance engines. Modern variable valve timing and, where fitted, variable lift systems also offer much more flexibility than the engines of years gone by.

But as your appetite for power grows, camshafts deserve a place on the shortlist.

 

Reading a cam card without reaching for a dictionary

Duration: how long the valve stays open

Duration is measured in degrees of crankshaft rotation. Longer duration can improve breathing at high engine speeds, but low-rev torque and drivability may suffer. A bigger number alone doesn’t tell you whether a camshaft suits your engine.

Compare figures measured using the same method. Advertised duration and duration measured at, say, 1.0 mm of valve lift are different things. Two cams both labelled “272 degrees” can behave quite differently. Besides checking the measurement lift, make sure the specification refers to cam lift or valve lift.

Lift and net lift: how far the valve opens

Cam lift and valve lift aren’t always the same figure. Rocker ratio affects valve movement, and valve lash must also be taken into account in a mechanical valvetrain. On Kelford cam cards, for example, Nett Valve Lift means the net lift at the valve.

Take Kelford’s 188-A2 profile for the SR20DET S13 as an example. Cam lift is 7.10 mm, rocker ratio is 1.55 and the specified net valve lift is 11.00 mm. Compare that 7.10 mm figure with another cam’s valve lift and you’re already comparing apples with something distinctly less apple-shaped.

More valve lift can help make use of the cylinder head’s airflow potential, but maximum lift doesn’t describe the whole profile. How the valve moves, and how long it spends at useful lift, matters too.

The famous OVERLAP

Overlap is a term you’ll often hear around those lumpy, choppy-idling American V8s. It describes the period when the intake and exhaust valves are both open as the exhaust stroke transitions into the intake stroke. Under the right conditions, it can help the engine exchange gases more efficiently. Its effect depends heavily on factors such as engine speed and intake and exhaust pressures.

A cam card may also list LSA, or lobe separation angle: the angular separation between the intake and exhaust lobe centrelines. In a single-cam engine, this is ground into the shaft. With separate intake and exhaust camshafts, their relative timing can be adjusted within the limits of the design. LSA alone doesn’t tell you everything about overlap, though, because duration and profile shape also play a part.

Doesn’t variable cam timing already take care of this?

Variable cam timing does help modern engines adapt their valve events to different engine speeds and loads. A conventional cam-phasing VVT system, however, shifts the timing of the existing profile. It doesn’t increase the cam’s physical lift or change its duration.

Some engines also have switchable cam profiles or variable valve lift. That’s why you need to understand your engine’s valvetrain before choosing parts. New cams may also require changes to the cam timing maps to make proper use of the mechanical upgrade.

Choose cams for the way you actually use the car

Before choosing a profile, ask yourself one practical question: where does the rev counter needle actually spend most of its time? A commuter, a track-day car and a drag car have very different needs, tempting as it is to roll all three into one. A rough idle and a high-revving race engine might sound brilliant, but they won’t necessarily do much for your trip to the supermarket.

• Street driving: prioritise throttle response and a broad, usable powerband.
• Track and drifting: consider the revs when exiting a corner and after each gear change. You may be looking at a very different profile.
• Drag racing: even a very narrow powerband can work if the launch, gearbox and gearing keep the engine right where it needs to be.

We offer different cam profiles for different applications. If you’re unsure which way to go, ask us for advice.

A cam upgrade needs supporting parts and tuning

Your cam upgrade budget needs to cover more than the shiny sticks themselves. The valve springs must keep the valvetrain under control with the new profile. Valvetrain mass and boost pressure also affect the requirements. Stiffer doesn’t automatically mean better. The spring package needs to suit the whole combination.

Some Kelford Cams profiles, for example, are designed for factory springs, while others require a spring upgrade. Always check the requirements for the specific profile you choose. Lifter and follower compatibility, along with any required valve lash adjustment, are part of the job too.

• Check mechanical clearances: piston-to-valve clearance and, where relevant, valve-to-valve clearance. On a VVT engine, check throughout the cam timing range you intend to use.
• Check the spring installation: correct installed height, spring pressures and sufficient clearance before coil bind. Retainer-to-valve-seal clearance must also be checked.
• Measure the cam timing: lining up the timing marks alone doesn’t guarantee the valve events specified on the cam card. Cylinder head machining, for example, can alter the timing.
• Tune, tune and tune again: the ECU calibration and cam control need to suit the new setup if you want to get the most out of the changes.

 

Kelford Cams: the right profile makes the difference

Kelford offers profiles ranging from mild upgrades to dedicated competition applications. The manufacturer’s application recommendations, cam card and valvetrain requirements tell you more than a single duration figure or a Stage label. Read them before the shopping basket starts filling up.

Well-chosen cams can give you exactly the engine character you’re after: a responsive street engine, a strong-pulling track companion or a race engine that loves the upper end of the rev counter. Not every engine needs to sound like there’s a drum lesson taking place under the bonnet at idle.

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