As we further break down modifications we focus on the Camshafts for this article many of us may know the ins and outs but some of us don't!
If cylinder heads are the heart of an engine, then the camshaft and valve train have to be the brains of the operation. Timing the opening, closing, lift, and duration of each valve event are central to increasing power and torque.
A valve train consists of valves and a mechanism which opens and closes them. The opening and closing system is called a camshaft. The camshaft uses lobes (cams) that push against the valves to open them as the camshaft rotates; springs on the valves return them to their closed position. This is a critical job, and can have a great impact on an engine's performance at different speeds.
The key parts of any camshaft are the lobes. As the camshaft spins, the lobes open and close the intake and exhaust valves in time with the motion of the piston. It turns out that there is a direct relationship between the shape of the cam lobes and the way the engine performs in different speed ranges.
The most commons camshafts are:
Single overhead cam (SOHC)
Double overhead cam (DOHC)
Pushrod
Single Overhead Cam Engines (SOHC):
This arrangement denotes an engine with one cam per head. So if the engine is an inline 4-cylinder or inline 6-cylinder, it will have one cam. If it's a V-6 or V-8, it will have two cams (one for each head).
Double Overhead Cam Engines (DOHC): A double overhead cam engine has two cams per head. So inline engines have two cams, and V engines have four. Usually, double overhead cams are used on engines with four or more valves per cylinder. A single camshaft simply cannot fit enough cam lobes to actuate all of those valves.
Pushrod Engines: Like SOHC and DOHC engines, the valves in a pushrod engine are located in the head, above the cylinder. The key difference is that the camshaft on a pushrod engine is inside the engine block, rather than in the head.
A Standard Camshaft
Why change your stock camshafts to higher performance ones?
They "CAN" give some performance benefit at higher revs though, but only if the rest of your engine and induction system and exhaust are also modified to take advantage! If not, the extra valve o "overlap" makes them sensitive to exhaust back pressure and your car may well be slower! Valve overlap happens when your engines inlet valve opens whilst the exhaust valve is still open. This aids airflow at high engine rpms
Cams types can be described (very general guide) :
(a) Stock - smooth, long lasting, good emissions, good economy, good low down power for smooth easy driving in traffic. The main manufacturers are not stupid! Think carefully before you decide on a "race" cam. Power falls away at higher RPM's.
(b) Towing, mild, or whatever - these will give good economy and will work much like the manufacturers stock cams. Standard lift and duration Usually expected top give more torque than stock ones at low RPMs Smooth tick over.
(c) Fast road camshaft - Usually works OK with stock head/valves and a good free flow exhaust system, and bigger better multi carbs. These will give a higher RPM peak power than stock and usually at the expense of some low down power. Remember that low down power is where you spend the most time in a road car. Usually a touch more lift and duration (about 260 / 270 degrees) Slightly lumpy idle in some cases. Gas flowed head and bigger valves helps if you can afford to do it, but generally not essential.
(d) Sport Cam / Very fast road - Not a sensible choice for road use, unless the car is also a race car and you can suffer a bit! Very lumpy idle on some engines, not smooth or powerful at lower 25 percent of RPM range. Peak power typically 1000 RPM higher than stock camshaft, big valves, ported head, free flow exhaust, multi carb or big throttle body, needed really to take advantage. Probably 20 percent more peak power than stock cam would give if the engine is as described. Lots of overlap, so high emissions likely. free flowing exhaust essential. 280 to 290 degrees, usually more than stock lift.
Cams in engine
(c) Race... Speaks for itself. in a road car far too much! To work, you need to have a totally "built" motor, with strong bits to stand much higher RPM than stock. And good head, big valves, open big bore exhaust (loud) and good free flowing induction system. High compression ratio needed as there is less time to "trap" the gasses. Much power! At high rpm only.
(d) Turbo or Nitrous Cams - These have stock (ish) intake timing, but less overlap, and high lift long duration exhaust timing, to get rid of all the extra gasses.
There are LOTS of aftermarket Camshaft manufacturers to choose from.
Companies such as:HKS, Greddy, Kent, MTS, ISKY, MAHLE, Comp Cams, Crane, Edelbrock among others.
