Hey guys. I am not sure what Compression is? What should it be at? Also, if I am only planning on 380 horses max on my car, should I change pistons? A guy told me that. But since stock internals hold up to 400, thats why it made me wander a little bit. I am just confused on this COMPRESSION stuff? I am not sure what Exactly it is?

 

Do you have the 420A or the 4g63? Have you done any mods so far?

 

mods dont have anything really to do with your compression. With your engine a good compression should be somewhere around 178psi. Most likely it will be alittle lower because of age but the service limit of the engine is 133psi. And when measuring the general rule is no cylinder should be further than 10% off. All the test is telling you is how well each cylinder is holding compression. Basically as you know cylinders will compress the air in each chamber. The compression ratio is just the volume in the chamber when the piston is at the bottom over the volume at top dead center. So if one or more cylinders are not holding this compression perfectly then you have a leak somewhere

 

How can I find out what my compression is?

 

Get a compression tester.

The compression for a turbo model should be 140-150ish

For the non turbo should be around 180.

 

From what ive read the compression should be around 145-170psi.

 

I am just a little confused on this stuff. But my friend said something about his compression being 9:01 ratio. and he said he though mine was like 16:1. Something like that. What is this ratio stuff?

 

woa thats not even close your compression ratio is 8.5:1 and if you read my first post i said what a compression ratio is basically once you know the compression ratio that will tell you what compression you should read. The general rule is...

(CR)(17-20) = compression

so if your car has a compression ratio of 8.5 (which is does) then you should read somewhere between 145-170psi. The service limit of the car is supposedly 133psi which means you read below that then you know the engine needs to be rebuilt. Or you might only get one or two that are bad, then you have a leak

 

So is it the higher the compression the ratio the better? Or the lower the better? Or does that not matter?

 

turbo models... lower.... and N/A engines higher