Books.

[Mr Speirs]

This is great!!! Im learning stuff too. At a guess a short cam duration would give better torque low down in the rev range and prevent the bike from bogging gown giving the rider a smooth response across the rev range and better fuel economy.
When the rider is looking for a more swift ride the long duration take over after a specific rev count and deliver more fuel and extract more gases and therefore more performance.
Am I way off the mark?

Timwilky suggested looking at 2-strokes and four-strokes, and I was gonna say that too; also, I was going to add that you should take a look at an uncommon engine design, the rotary engine. Norton used these in some bikes, and Mazda use them on the RX7 and RX8. An intresting engine, and retains those basic principles of how to generate power...but has some fundamental flaws which make the conventional 4-stroke engine favorable (identify these flaws, if you will!)

good website I used to read alot: www.howstuffworks.com

Matt

Okie doke matt, that's something for me to do when I get home

Mr speirs, it sounds like a vtec engine you're describing. Two different lobes, the other is pushed into place after 7k rpm (If I remember from riding dads) by higher pressure oil moving the shaft along. (I think)

[yorkie_chris]

Nonono ... you misunderstood the question, perhaps I should have phrased it in more than one word...

Why does a short duration cam give better bottom end, and why does a long duration cam give top-end?

[yorkie_chris]

P.s ... matt, the rotary engines use exact same flow cycles as a normal 4 stroke, just doesn't have any cylinders.

Wow, I'm liking the look of this thread already, I can see I'm going to learn lots yey!

Originally Posted by yorkie_chris

Nonono ... you misunderstood the question, perhaps I should have phrased it in more than one word...

Why does a short duration cam give better bottom end, and why does a long duration cam give top-end?

Ah, ok.

A short duration cam gives better bottom end because the exhaust gases don't have enough time to move back up the intake tract, as happens on a longer duration cam.
With long duration cams, there is overlap (where both intake and exhaust valves are open at the same time). With higher engine speeds, the gases don't have enough time to go anywhere but out the exhaust valves, like they do at lower engine speeds.. Then when the intake valve opens, the overlap helps get the air into the cylinder faster. Because both are open at the same time, the intake valve is getting the mixture into the combustion chamber while the gases are still going out of the exhaust valve, so by the time the exhaust valve closes, the intake stroke has had a head start, if that makes any sense. Thus, it makes more power at higher revs than lower revs.

At least, I think so

[yorkie_chris]

Yarp.

What is ignition advance, what are the effects of advance, what happens with too much advance, how is this related to the fuel used?

Matt-
Because there is such a long combustion chamber and low compression, the engine is much less efficient

I like the engine though, its very smooth

[yorkie_chris]

Why does long combustion chamber reduce efficiency then?

(p.s trying to get you to think about cause and effect rather than just "what happens when you do "x""...)