why does compression matter?
i always see something like 10:1 or so, what does that mean, and what do the numbers mean, and is higher to lower better... etc...

thank you!

 

compression is hard to put into just a few words...

compression is basically the area between the piston top and the head bottom(or combustion chamber).

but there are lots of variables that come into play with that, such as head, i have heard a b18 gsr head over a b16 head will raise the compression a bit...

it all depends on your setup, weither or not you want higher or lower compression

10:1 on an N/A setup - not so fast
10:1 on a good turbo setup - Can be fast(lost of variables)
14:1 on an good N/A setup - fast(but can go boom)
14:1 on a turbo setup - will go boom(i dont even think methanol would help it)


the compression numbers that people talk about alot are static compression numbers. or N/A numbers. But if you are turbo charged there is a Dynamic compression ratio that come into play, but people usually post about static compression numbers because this is the one you use when you order pistons.

i cant remember the conversion but this is close

9.5:1(static) compression turbo charged to 14psi is like 14:1(dynamic)

someone else need to chime in and explain the meaning of the numbers

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Ideal &raquo;</TD></TR><TR><TD CLASS="quote">why does compression matter?
i always see something like 10:1 or so, what does that mean, and what do the numbers mean, and is higher to lower better... etc...

thank you!</TD></TR></TABLE>

i dont really know all the physics in it, but this is what i do know...

compression like the word seems, is how much your motor is compressing air.
on a NA motor, you want high compression. the higher the compression, the more air being forced into your cylinders. the more air, combined with gas = more power.

now for a turbo car, we tend to go low so we have room for error. now there are poeople that go with higher compmression (such as 10.1, which is moderate for a turbo car), but for the most part, people that i know stick with 9.1. now the reason we can still make power with low compression motors on turbo cars is due to the turbo. the turbo compresses the air, and then it goes into your cylinders. due to the density of the air molecules being increase compared to a NA(more air molecules b/c it waas compressed) you will get bigger explosions, so more power.

if i went wrong somewhere someone correct me

 

You guys are right. I think the easiest way to explain compression is like this... pour some gun powder on the table and light it. What happens, a few sparks not much. Take that some gun powder and wrap it tightly with some paper light it. Now what happens. Boom that's what. Now whats a compression ratio. How much your compression your combustion chamber. The higher the number the more your compressing the chamber. More compression makes more power. However too much compression makes to violent of an explosion which can cause your motor to blow. Hence turbo cars run lower compression than NA cars. What effects your compression ratio? Lots of things. Pistons, rods, crank, head, head gasket, these all can effect your final compression ratio.