compression question

[quad_man08]

i pretty much know what 12:1 and 11:1 means....the higher you go the more power and stuff you get. but what do they actually mean? just wonderin if anybody can explain it to me

[400exfan19]

it tells u the size, bigger the better

[ride_red666]

the higher u go the bigger compression but i think 11:1 is the highest on pump gas 12:1 u can get by with a 50/50 mix of pump and race gas. not always better but definetly more power just less reliable

[ImplodedMindZ]

Degree to which the fuel mixture in an internal-combustion engine is compressed before ignition. It is defined as the volume of the combustion chamber with the piston farthest out divided by the volume with the piston in the full-compression position (see piston and cylinder). A compression ratio of six means that the action of the piston compresses the mixture to one-sixth its original volume. A high ratio promotes efficiency but may cause engine knock.

I just coppied that off some site. you will probably find the best answere if you just go to google and type in compression ratio so many sites will come up giving discriptions and wantnot.

[wilkin250r]

Yep, that's the definition, but it gets a little too techno-speak for most people to stomach.

Let's use a real simple example. Let's say you had an engine that pulled in 400cc of fuel/air mixture, and then compressed it to 40cc before ignition. What is the compressio ratio? Simple, it's 400 divided by 40, or 10:1.

If you had 400cc, and compressed it to slightly smaller, like 36cc? You'd have higher compression, 11:1.

When your engine is stock, it actually has 439cc of space inside it. The piston pulls in 397cc of air, and compresses it into 42cc of space in the head. (add the total, it's 439). This space is called the "combustion chamber". This gives a compression ratio of 397/42, or about 9.4:1

When you add a high-compression piston, it has a dome on top that takes up some of the space of that combustion chamber. Now the space is smaller, like instead of 42cc, you might have only 36cc. You still pull in the same 397cc off air, but squish it into 36cc. This would give you a compression ratio of about 11:1.

[pit/wood]

I tried to explain that in a thread once. You did it alot better than I did.

Now if you could go a little further and touch on strokers you will have a sticky to post:D :D :D :D :D :D

[blown331]

stroker would just allow MORE air initially to be brought into the cylinder then compressed to X ratio depending on piston.

[Kaleigh]

im not sure if this is right.. someone tried to explain to I would understand..12.5:1... it compresses at 12.5 times the pressure of what has came into the cylinder.. is that right??? this is one thing I was never good at.. so if someone can make me understand then anyone can understand..lol...

[44oEX]

it would mean that it would make the air go in a space that is 12.5 time smaller then the size of the original space.

[krt400ex]

Originally posted by Kaleigh
im not sure if this is right.. someone tried to explain to I would understand..12.5:1... it compresses at 12.5 times the pressure of what has came into the cylinder.. is that right??? this is one thing I was never good at.. so if someone can make me understand then anyone can understand..lol...


say u have 12 cubes that r one in around..u have 12 cubic in. then if u compess those 12 cubes together into one cube that is 1 in around, u will have compressed them from 12 to 1. get it?

[Kaleigh]

YEAH>>> thanks so much man.. thats a really easy way of explain..

much appreciated ^_^

[krt400ex]

no prob