How do uprated cams work?

[Byard]

Do they just open the valves more than normal and therfore let more air and fuel in and let gasses escape quicker?

[Colin]

They hold the valves open for longer and further, so more air/fuel is drawn in. Tuning the valve "overlap" is key to good running too. In a nutshell.... :p

[Sparco_Tom]

nail on the head ^

[Byard]

Thought so, thanks Colin :y:

[Toad]

If you look into it a little deeper, it's quite interesting how performance camshafts work. They change the valve opening and closing times in such a way, that they help keep a constant acceleration of the air / fuel mixture into the cylinders.

When the piston moves upwards on the exhaust cycle, the inlet valve opens a little early, allowing the flow of fuel / air to maintain momentum. The exhaust valve will be open at this time too, so there'll be some waste, and also a rough idle. "overlap" is actually really difficult to describe IMO.

Take a look here, this web site is excellent: http://auto.howstuffworks.com/camshaft.htm

[Saaamon]

http://www.motorsport-developments.co.uk/tech_articles/FAF245_tech.pdf