Performance Tuner visits Piper Cams to separate camshaft fact from fiction.
Camshafts – frequently and criminally skirted over when talking through a performance tuned car’s specification, when ‘oh and a set of spiky cams’ is almost added as an afterthought...
Piper Cams is one of the most well-established and respected names in the field. Established in the mid 1960s, to meet the huge demand for performance camshafts for the likes of ye olde Ford Anglia and BMC Mini, the company started out using a modified crank grinder. “At that time we did a matched cylinder-head and cams” says Ian Cox, managing director of Piper Cams. “They were called Green (Stage I), Yellow (Fast Road) or Red (Race). They all had different specifications – the Green one would have standard valves, the Yellow would have an oversized inlet and Red would have the ports machined to match. These cylinder heads were then matched with each cam. It was quite successful, even then there was an air of sophistication about it, but the actual procedure for making it was relatively crude.”
All of which seems rather a long time ago now, with work undertaken for a wide range of clients from FIA GT racing teams, car manufacturers (no names please, client confidentiality), engine builders and of course the performance tuning market.
Treating the cylinder head and camshaft as separate entities is basically asking for underachieving trouble, because they depend upon one another to produce the figures you want. Think of them as an accomplished double-act upon which you are counting to get a good laugh; ignore this and it would be like Wise without Morecambe, Hardy without Laurel. In short, your tuned engine will be grossly compromised and nowhere near its optimum capabilities.
Just like a good performance cylinder head, a camshaft is all about airflow – get too little or even too much and you will have wasted money. In other words the cylinder head’s airflow dictates the camshaft specification – not the other way around.
“You’ve got to relate the camshaft to what’s been done to the cylinder head,” says Ian. “If it’s a standard head and you know that there’s a problem with the flow then you’ve got to use a camshaft that’s going to work.”
ENGINEERING THE CAM
John Crabb, Piper Cams’ Technical Director, explains the process behind engineering a new camshaft: “We basically design valve motion, we just go back to design the shape of the cam and that valve motion is all about how much air you flow with everything bolted on.
“The first thing we do with a new camshaft, is put the cylinder head on a flow bench to see how efficient the ports are. Generally we can always make it better because the standard OE parts have different design criteria – such as emissions, etc. After we’ve flowed the head, we then put the inlet manifold on to see where the weakest link is – to evaluate how efficient the standard port is – and then we do the same with the exhaust. There’s no point just flowing the head, because all the other components reduce the flow rate.
“You’ve got to address the engine’s needs, which is why we make all the exhausts too – and there’s hardly anyone who does that. Once you’ve sorted out the cylinder head and start reassembling it, you can see where the bottleneck is because you’re losing power – and that’s where you spend the money. It’s amazing how many people spend a lot of money on a cylinder head and then bolt the restriction back onto it afterwards.
“Ideally you don’t want the inlet port to be polished because the fuel droplets hang on the wall and you use that to break or mix the air with the fuel (unless you’re running fuel injection which runs under greater pressure of course). It’s all about the shape of the port, getting the mixture in as smoothly and quickly as possible, otherwise the airflow can vortex and break away. You can actually hear it in the port – it makes a horrible squealing noise when it all goes out of control.
“After that you do a curve which shows you when the air rolls over at a certain valve lift – this allows you to design a camshaft with the maximum lift for the airflow. The OE component will be quite a way short of optimised lift – say the airflow dictates a 10mm lift, the OE lift will be around 8.5-9mm. We can neutralise that lift and the area. As for exhaust flow, it should be at 80 per cent of the inlet flow.”
What about performance tuned cylinder heads? “The problem is that everyone ports their cylinder heads differently. Our Fast Road cams aren’t a problem because they’re designed for standard cylinder heads and we know what their flow rates are, so generally they’ll work quite well. Beyond that, after people have fitted bigger valves and changed the port sizes, you have to make a ‘guesstimation’. Although most companies know what they’re doing, so it should flow X-amount more air and it should peak over at 600 or 500 thou’. Unless you’ve got all the valve gear, inlet and exhaust manifolds you can’t get it exactly right, so you have to compromise,” says John.
“What we look at next is valve train geometry – whether it’s directly operated or whether it’s push-rod. If you start accelerating the pushrods too quickly, you get buckling and it all gets out of control. So after we’ve designed a camshaft profile, we go back and make sure that there aren’t any harmonics or problems with the push-rods, etc. The standard valve springs also have to be inspected, again to make sure that they can cope and if they can’t, then we have to design a new valve spring with a suitable spring cap.
“When we design the valve springs we make sure that they match standard OE fitted length with a spring cap, so the customer doesn’t have to machine the platform. This is because if you design something which requires machining then it’s expensive, plus it can be hard to find a local machine shop, so we try and package everything in without it needing machining.”
Lift and duration are probably two of the most commonly heard pieces of camshaft parlance (see sidebar), but is it possible to have too much of a good thing? Well, certainly with duration – which is the time the valve is open from the start to the end of the cycle. You want as short a duration as is physically possible (which also reduces the amount of overlap) and this is certainly the current thinking behind modern higher lift cams. The danger with a long duration is that the valves are open for longer at Top Dead Centre (TDC) so the mixture goes straight in and then out, making it very inefficient.
“The problem when you try to combine high lift with a short duration, is that there isn’t much time,” explains John. “This means that everything has to speed up and it can lead to problems with dynamics and positive acceleration where the valve tops can break off.”
Lift is also another thing which can be supplied in excess, particularly when airflow is dropping off. There’s little point in going for a huge amount of lift if there isn’t the available airflow to utilise it; in effect all that is happening is that everything is being put under unnecessary additional stress.
“Airflow is basically governed by the minimum port diameter and the size of the valve – there is a maximum volume it can flow. The smaller the inlet port, the faster the speed of airflow – an inlet with a 1 inch diameter equals an airspeed of 110 metres per second. Again it’s important to get the right port area to valve area for maximum flow,” says John.
Become conversant in cams and the message is a simple one. If you are intending to modify your head, install a cam which has been designed to suit the spec of your cylinder head. Then you can sit back and be confident that you are reaping genuine power gains from an optimised tuned cylinder head. Just remember to give the camshaft its fair dues...
