compression ?

[EFeffect]

i would like to know if any one can explain compression ratios to me... and how you tune it? by the way i love this forum and have learned some much information... keep up the good work!

[drivinacivic88]

I will explain.

Compression ratio is basically the ratio of the volume in a cylinder from bottom dead center (BDC) to top dead center (TDC).

This picture shows an engine with compression ratio of 15:1.

The volume of the cylinder when the piston is at TDC is always 1. This is the second number in the ratio.
The volume of the cylinder when the piston is at BDC is dependent on the volume at TDC.
Basically, if you have a 15:1 compression ratio, it means that your pistons are compressing the volume of air in your cylinder by 15 times.

Does that make any sense? Hope so...

As for tuning your compression ratio, there are a few ways you can do it:
1. Swap your crank shaft out with one that offers a longer stroke than your current one. (this uaually requires changing your connecting rods out to shorter ones so that you don't send the piston through the block)

2. Swap your pistons out. (pistons usually have an inverted dome on the top to allow for valve clearance. If you swap them out for something with less of a dome, or even a flat top, that will boost your compression ratio a little)

3. Adjust your valve overlap. (easiest to do on DOHC engines.) Less valve overlap will give you slightly higher compression, while more overlap will lower compression. This is not a method i would suggest for anyone who doesn't have some serious knowledge about their engine.

[EFeffect]

what would you recommend doing for a 1.6 sohc non vtec zc motor

[drivinacivic88]

Sadly, I don't know enough about the ZC to even guess how to get better compression out of one. Sorry

[el_jelly]

I haven't seen many high compression na builds on the zc, most of them are turbo which responds very well on that engine.

[momo182]

get a compression tester!! these things are amazing they show you the condition of the cylinders without having the engine run... a must have for all techies!!

[cougar289]

get a compression tester!! these things are amazing they show you the condition of the cylinders without having the engine run... a must have for all techies!!

Even better: a leakdown tester.

[drivinacivic88]

get a compression tester!! these things are amazing they show you the condition of the cylinders without having the engine run... a must have for all techies!!

Even better: a leakdown tester.

Both have their advantages. I like the leak-down better though. But neither of those will help increase your compression ratio.... Lol