Performance camshaft

For an engine to make more power, it has to take in more air. In most four stroke engines, the air must enter the combustion chamber through the valves. The camshaft controls the opening and closing of the valves by regulating the time that the valve is opened and closed, and how much the valve is opened by. An easy solution to have more power, would be to alter the characteristcs of the camshaft so that it either keeps the valves open for a longer period of time, or lift the valve higher off it's seat so that more air can pass into the combustion chamber. It all sounds very easy, but once again, there's more to it than meets the eye. Like most engine mods, this one is also a compromise.


In the perfect engine, the inlet valve will open when the piston is at TDC (top dead center), and as it travels down the bore, it will suck in a full charge equal to it's displacement. The exhaust valve would open at BDC (bottom dead center), and the full displacement of spent gasses would be pumped out of the engine - the perfect engine running at 100% volumetric efficiency. In practice, the stresses on the valvetrain would just be too much for the materials to handle. To lift a valve of say 50g some 10mm off it's seat in less than a millisecond (at 6000rpm) without it bouncing or doing anything untoward in the next 100 000km of it's life, simply doesn't work with the materials in use today. So, the manufacturers used their multi-million dollar research budgets to come up with a simple solution.

The piston travels rather slowly at TDC compared to the middle of the stroke - there's not much of the pumping action being done in the 10 or 20 degrees around TDC. So, they start to open the valve gently while the piston is still on it's way up on the exhaust stroke. Although this creates valve "overlap" (time in which both the intake and the exhaust valves are open), it does allow the engine to breathe better and create more power.

When the time that the inlet valve stays open is made longer, the overlap starts to become a problem at low engine speed. The exhaust gasses get pumped into the inlet tracts, substantially diluting the incoming charge and causing the engine to run very poor. That's why an engine with a wild camshaft runs uneven at idle - it's choking in it's own exhaust gasses. However, when the engine speed goes up, the exhaust gasses pick up momentum, and during the overlap period, the departing exhaust charge creates a partial vacuum behind it, sucking in more of the fresh intake charge.

This leads us to two important conclusions: Firstly, the wilder the camshaft, the less power the engine will make at low rpm. Such wild engines will normally not have enough power at regular "civilised" driving speeds to pull the skin off a rotten banana. To pull away from a stop, you will have to rev it up to come "on the cam", or stall the engine at every attempt at a civilised getaway. Secondly, the engine will only produce more power at the very top of it's rev range. These are important points to consider when choosing a racy camshaft for your engine. Are you willing to sacrifice low speed drivability in exchange for more top end power? It's up to you to decide.

No, I m not against performance camshafts and want to point out the facts to you so you won't end up wit a car you hate. Driving such a car to work every day soon starts to get on one's nerves. And if you transport passengers in your vehicle, be warned : they are usually not very sympathetic towards the neck-wrenching style of driving that such a vehicle demands to keep it "on the boil". If you do decide to go with a hairy cam, there are a few things you can do to slightly alleviate the associated low speed problems.

A good free-flow extractor exhaust with long primary pipes tuned to low engine speed optimisation can make the engine come on the cam a little sooner. The long 4-into-1 systems seem to be able to "pull the engine on the cam" a little sooner than the regular banana style 4-into-2-into-1 systems.

Long ramstacks on the intake. What is a ram stack? It's those shiny flared tubes you often see on the carburettors of high-performance engines. These artificially create a longer intake path for the air, allowing it to build up some momentum. They also have an added benefit that they can allow up to 8% more flow into the carb when compared to the usually blunt ending of the carb mouth.

Proper gas-flowing of the cylinder head. A lot of cylinder heads out there flow more air in the wrong direction than they can flow in the right direction. Most people who gasflow cylinder heads don't even realise that they are making it easier for the gasses to also flow well in the wrong direction! Remember that the main problem is that the exhaust gasses flow into the intake port during the increased overlap period. I can put you in touch with people who can do special things to a cylinder head so that it is difficult for the exhaust gasses to pop out through the intake port in the camshafts' overlap period. There's a whole science behind optimising the head to make it "cam-friendly", and usually there is a substantial improvement in the low speed range if the cylinder head is flowed properly, by a person who knows what directional flowing is about. Note that it is easy - even for experienced "port grinders" - to completely ruin the reverse-flow characteristics of your cylinder head.

Match the engine controls to the camshaft. The different profile of the camshaft plays havoc with the fuel injection's standard factory mapping. The ignition timing and mixture requirements of the engine is vastly different to that of a standard engine. The way I would recommend to do this, is to fit a CHIP. The engine can be run on a loading type dynamometer, and the engine management system can be reprofiled to match the specific engine's state of tune. The unichip is perfect for modified engines, because of it's ability to be reprogrammed whenever needed, i.e. if you decide to make more mod's, you simply have the unichip reprogrammed to match your new requirements. You don't have to throw it away like a conventional, old style "chip".

See how the camshaft is born by Comp Cam.