Okay, so I've been trying to understand this whole compression ratio thing and whatever, but I dont get it. What IS the compression ration?

 

Basically, it is how much the air is "crushed" from it's original size. The difference in volume of air before and after compression.

 

The ratio of the cylinder volume with the piston at bottom dead center to the cylinder volume with the piston at top dead center.

 

So that means the higher the compression, the more power. Does that mean that if the compression is higher, there has to be more fuel?
How is high compression achieved? By making pistons drop lower and then rise higher so the air is compressed even farther?
How are cams and valves and valve springs related to the compression?
How what affects does forced induction have on high compression engines? And what compression rate is too high?

Lol, i know that's a lot of questions, but I really want to learn all of this and I don't have the time or money to go buy books

Thanks!~

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Commiecircusbear &raquo;</TD></TR><TR><TD CLASS="quote">So that means the higher the compression, the more power. Does that mean that if the compression is higher, there has to be more fuel?</TD></TR></TABLE>

Yeah, if adding air, you have to add more fuel at the correct ratio

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Commiecircusbear &raquo;</TD></TR><TR><TD CLASS="quote">How is high compression achieved? By making pistons drop lower and then rise higher so the air is compressed even farther?</TD></TR></TABLE>

No, you are referring to the stroke, although compression ratio changes can be made by where the wrist pin is located. It is mostly designed into the quench area and or dome of the piston and the shape/size of the combustion chamber in the head.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Commiecircusbear &raquo;</TD></TR><TR><TD CLASS="quote">How are cams and valves and valve springs related to the compression?</TD></TR></TABLE>

Well, for the most part, the have little effect as far as actual compression, but if they are not sized correctly for how much air the piston can pull in, then that could lower compression.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Commiecircusbear &raquo;</TD></TR><TR><TD CLASS="quote">How what affects does forced induction have on high compression engines? And what compression rate is too high?</TD></TR></TABLE>

Forced induction increases the likelihood of detonation in high CR engines, because a static compression ratio is just that, a ratio. So if you start with compressed air to begin with, when increasing it, the pressure can get too high(increasing heat) and cause the mixture to ignite before the spark plug does this. That is called detonation, or pinging, or knock.
This same symptom is when you know compression rate is too high, because the mixture cannot stay cool enough to ignite at the correct time. Retarding the ignition timing or running cooler plugs can help alleviate this, but only so much.