Automotive Performance Information
Automotive Performance Information

Friday, November 16, 2007

Cams, or camshaft, and effect on performance

Wild or "race" cams are just not suitable for a road car. They do not allow you to drive smoothly in say 4th gear in town because they make your engine run "lumpy" at low revs! And you will have an uneven idle like a bike engine.

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.

On the other hand, if you have just spent a fortune building a "big valve" race engine with lightened and balanced internals etc it would be stupid to fit a standard camshaft, as most of your hard work would be wasted! Like everything in life it has to be a balance. So its best to know what you are looking for and plan for that! Its no use just putting a few go faster bits on your car and hoping! That does not just apply to camshafts but to the complete engine. All the bits need to be matched and work together! You must have a plan before you start.

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.

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. Think "Bike engine"!

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:

Kent, Piper, Crower, Holbay, MTS, ISKY, MAHLE, Comp Cams, Crane, Edelbrock, Erson, H.O., Indian Adventures, Iskandarian, Lunati, Speed-Pro, Summit, Ultradyne, Systrand , Schrick Camshafts, Wolverine, Lazer Cams to name just a few!


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Automotive Performance