Cams have to be about the most complex subject in tuning, and you could write a (pretty damn boring) book on them to cover it all. But what do cams actually do?
Well, basically they operate your engine’s inlet and exhaust valves, opening and closing them at the right moments to allow your engine to run. By making changes to when your valves open – how far they open and how long they open for – you can transform how your engine performs…
LIFT AND DURATION
The two main things you can adjust by tweaking your cams are lift, which is how far your valves open. And duration, which is how long your valves are open for. In performance terms, higher lift gives improved power with very little loss of low rpm performance.
But you will be limited to how much is possible without the valves colliding with the pistons or causing excessive wear to the cams and valve train. Unlike lift, cam duration is a very give-and-take thing, and while increasing duration can boost top end power, it usually also decreases low rpm power by a similar amount.
For this reason full-on race engines that barely go below 7000rpm run super long duration cams. But most road-going engines run shorter duration cams for more useable low-rpm performance.
VARIABLE VALVE TIMING
Many cars these days have some form of variable valve or cam timing, such as the famous Honda VTEC setup. While we won’t bore you with how it works. This means you can have the best of both worlds from one set of cams. A sensible mode for low-rpm driveability and economy, and a bonkers mode for high-rpm mentalist power. Awesome!
SINGLE AND MULTI-CAM SETUPS
It doesn’t take a genius to work out how many cams a quad cam engine has, but why do engines have differing numbers of cams? The most basic is a single-cam engine, and this means the one cam controlling all the valves. On a straight engine it means you have two cams, one controlling the inlet valves and one controlling the exhaust valves.
The main advantage of this in tuning terms is that more adjustment is possible. In a ‘V’ or ‘flat’ engine design, twin-cam means one overhead cam per head, with each working like a single-cam. Finally, quad- cam is just like twin-cam on a straight engine, but a V or flat engine has two cams per head.
WHAT, NO CAMS?
Not all engines even have cams. Mazda rotary engines and many two-stroke engines have none at all. On a conventional four-stroke piston engine though, cams and valves are vital. Unfortunately, the force required to open valves is huge, in fact around 25 percent of most engines’ power at idle speed. Because of this, if there was no need for cams and valve springs, engines would be far more powerful and economical.
Unsurprisingly many manufacturers have realised this. Designs using electromagnets, instead of cams and springs, to open and close the valves are in progress. While none are available for production cars yet, it’s certainly the future. It will allow levels of valve tuning that’ll make a VTEC look like a steam engine.
DON’T GO TOO FAR
Like most fun things, with cams there’s such a thing as too much. In fact too much cam can make your car run really badly. The lumpy idle and a high rolling road bhp figure from some lairy cams might make people think your car is fast, but when you have no low down power and a tiny power band, it’s at best a pain in the ass to drive. And at worst, not actually very fast.
With N/A cars, especially ones without any form of variable valve/cam timing, you will always be giving away low down power to gain high rpm performance. So make sure the rest of the engine is just as wild, or all you’ll do is lose low-down grunt, without gaining anything worthwhile up top.
With turbos and superchargers it’s even easier to have too much cam. While a pair of fast road cams in your otherwise standard naturally aspirated engine may wake it right up, the same cams in your standard turbo or supercharged lump could make it lose a ton of low-rpm performance without gaining anything on the top end.
In some cases we’ve seen cars lose peak power with OTT cams. As your tuned turbo and supercharged engine specs get wilder, so do the worthwhile cam specs, but compared to a N/A engine, it’s always quite mild. It’s often possible to double the standard power on a turbo car with stock cams still fitted, and even fitting the cams from the lower power N/A version of your engine is usually an upgrade. Don’t go too crazy!
Pop in a set of cams and gain 25bhp? It’s rarely that simple. Here are a few more things that often need changing…
Uprated valve springs – These stop the springs becoming coil bound or being forced open by boost pressure or exhaust back pressure.
Adjustable cam pulleys – Used to precisely set up aftermarket cams, they look damn pretty too.
Notched pistons – Many wilder cams require modified pistons to stop the valves crashing into them at full lift.
Solid lifters – Most cars have hydraulic lifters, but these can’t cope with seriously wild cams, so a solid lifter conversion needs doing. More maintenance is required, and a bit more engine noise, but it’s worth it.
Uprated cambelt – Not vital, but when you’re revving your car higher and harder, it’s a wise and cheap upgrade on many cars.
Modified head – There’s only so far you can go with cams until your head needs work. From oversized valves and bigger ports, to a bit of grinding to stop the giant cam lobes whacking into the head. It all needs doing when you’re building an engine with wild cams.
ECU Remap – Even the mildest cam swap will benefit from the fuel and ignition settings being tweaked to take advantage of the increase in airflow the cams have given…