Compression Right??
 

Hey guys, if you guys can help me out. Im running vitara pistons in a JDM D15B. I know the compression is 8.5:1, BUT i dont know how to find out what the actual lbs is supposed to be. Before i changed the pistons, the stock PO8's were at 155 when i ran a test, but not its 90. Now, it is 90 across the whole block, but that still sounds kinda low to me. Can anyone tell me what it is supposed to be or if im good?

RE: Compression Right??
 

hhmmm... 90 sounds awefully low. I just saw a chart showing what compression test readings should be judging by actual motor compressoin. Let me look around and see if I can find it

RE: Compression Right??
 

Now, i can think of two things, since the car has not actually started yet gas has been pumping in the cylinder, the rings got washed and i need to add some oil OR just because the car hasent started, there has been no vacume and the rings have not pushed against the walls properly. Im thinking of putting some oil in the cylinders to see if the compression goes up, but i have nothing to compare it to. I need a base number that im supposed to be at.

RE: Compression Right??
 

u mean u havent started the engine since u put the new pistons in??

if thats the case then u have to seat the rings first so they can seal properly

RE: Compression Right??
 

Correct, but if you have read my other posts, you will see my car wont start. I have tried everything, so i really am hoping when i ship it off to a shop and it cranks up, the comp numbers go up. But like i said, with this motor and pistons, what SHOULD it be?

RE: Compression Right??
 

The chart I posted in your other thread comes from a mechanical engineering and a recip engine vetern. Go off of it. And like I said in that thread, your rings haven't sealed yet, so compression readings will be low until they seal. Take a reading after the engine has been broken in.

RE: Compression Right??
 

I dident see a chart, but i cant break in the engine, because it wont start, because the compression is so low and the mixture is blowing by the unset rings. So, im going to try to put some oil in the cylinders to see if i can bump up the compression enough to get some combustion.

RE: Compression Right??
 

Here's a general guide to compression.

Engine—What is a healthy engine???
Compression test results should be as follows:

* 8:1-8.5:1 compression: 150-170 psi per cylinder
* 8.5:1~9.5:1 compression: 170-210 psi per cylinder
* 9.5:1~11:1 compression: 210-275 psi per cylinder
* 11:1+ compression: 250+ per cylinder (highly depends on cams being used)

Your rings aren't sealed yet I presume. Break them in and see what you come up with.

Was my post.

RE: Compression Right??
 

well, i guess that gives me a good general idea, but since i cant start the motor, i cant get the rings to set, therefore cannot get good reading.

RE: Compression Right??
 

I'm not an expert trouble shooter here, but could your af mixture be too rich?