Does a cam effect compression

[MAD450r]

Honestly, I want to know if by changing the cam in my 450r did I cause the compression to go up ?

[plkmonster2]

Yes, it could have. With a longer duration, and more lift, the engine is able to grab more air, and the more air, the harder it is to compress the air. Although the actual compression may have gone up, your compression ratio would not.;) Does it seem harder to kick, or what?:)

[MAD450r]

no idea I bought it with the hrc installed added the pipe after the second oil change.

Was just wondering, a freind and I were discussing it is all

[wilkin250r]

Your compression ratio is theoretical. It's just a useful tool to describe the pressure inside your cylinder. Generally, the higher the compression ratio, the greater the pressure inside your cylinder.

Here is an analogy. Theoretically, a 450r will beat a 400EX on a race track. Is this absolute? No, it really depends on the setup of each machine and the skill level of the riders, along with a little luck. So what good is the theoretical? It's just a useful tool for description, but it isn't an absolute determination of real-world performance.

So, if compression ratio is just theoretical, what actually matters in the real world? Cylinder pressure. And to answer your question: Yes, a cam can cause the cylinder pressure to increase. In fact, you could say a cam always causes an increase in cylinder pressure, though usually only in the upper RPM range. They can actually have lower cylinder pressures in the lower rpm range as a side effect.

I can go into lots more detail if you're not bored already...

WOW am i stupid!!! i though compresion ratio was the ratio that gas and air that enter your combustion chamber were compressed. I didn't know it was theroretical. Thanks Wilkins!!!!!

[86atc250r]

Well, I wouldn't really say it's theoretical - there are two different things we're looking at.

The one we all go by is known as static compression. This is a hard number that is calculated from known values that don't change for a given engine design unless you change parts or grind on stuff. It gives you somewhat of a baseline to go by when making comparisons.

However, an engine is a dynamic beast - volumetric efficiency changes with pipes, cams, the way the head flows and any of a number of other factors --- not to mention that RPM changes the way everything interacts & causes volumetric efficiency to change "on the fly".

So -- dynamic (real) compression is definitely affected by the cam you choose. However, if you're just wanting to quote your static compression ratio to people - no, your "compression" doesn't change with a cam ---- if that makes sense :)

[pead_24]

You guys make me feel dumb lol :rolleyes:
but i understand what yous are saying