Ran a compression test.. thought I was going to be disappointed.. seeing as my last GSR with 150k dropped 230 across the board..

Either my tool reads high *** #'s or I just luck out on strong motors..

This GSR has about 75k on the dot and I did 235-240 depending on whether or not I gave it that 7th crank...

guess it's a good canditate for boost

 

As long as you're consistent across the board your in good shape. 28 psi is max variation psi before you have to do something.

 

Can someone explain to me what a compression test really is? For instance, what do the #s mean? My friend did one on a SR20DET motor and it read 175 all across which is supposed to be very good, how come it's so different between these 2 engines?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 94TealCivic &raquo;</TD></TR><TR><TD CLASS="quote">Can someone explain to me what a compression test really is? For instance, what do the #s mean? My friend did one on a SR20DET motor and it read 175 all across which is supposed to be very good, how come it's so different between these 2 engines?</TD></TR></TABLE>

 

It tells you the condition of your motor after you do all of the cylinders in the motor. Low numbers can be various things such as bad piston rings, a bent rod, or have a bent valve. Doing a valve adjustment may bring up your numbers a few points depending on how out of spec they are. The main thing you want to have is numbers that are as close together as possible across the board. 20-25 psi being the maximum variation between cylinders before you should look into replacing internal stuff.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VTECorona &raquo;</TD></TR><TR><TD CLASS="quote">It tells you the condition of your motor after you do all of the cylinders in the motor. Low numbers can be various things such as bad piston rings, a bent rod, or have a bent valve. Doing a valve adjustment may bring up your numbers a few points depending on how out of spec they are. The main thing you want to have is numbers that are as close together as possible across the board. 20-25 psi being the maximum variation between cylinders before you should look into replacing internal stuff.</TD></TR></TABLE>


hmmm.. valve adjustment has no effect on compression

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 91integraLSVTEC &raquo;</TD></TR><TR><TD CLASS="quote">


hmmm.. valve adjustment has no effect on compression</TD></TR></TABLE>

How do you figure? Do you know what makes compression possible?

Let me fill you in on what valves do. Ok as the piston goes up, depending on what stroke its on, close or open. If it is on the compression stroke then all valves close creating a seal in the cylinder. If valves are not to spec, they will not create a perfect seal, thus not creating max compression. If you don't know what you're talking about, don't comment and make people believe false info.

 

what do the #s mean? I mean what are they a measurement of?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 94TealCivic &raquo;</TD></TR><TR><TD CLASS="quote">what do the #s mean? I mean what are they a measurement of?</TD></TR></TABLE>

The amount of pressure in each cylinder. Since a motor functions like a pump, you want a good seal in each cylinder, which will result in better compression numbers. If a cylinder is lower than the others then there is not a good seal which means you have a problem somewhere.

 

When I did mine, i got 225-230 across all four cyclinders, however the next day I couldn't remember if I turned the engine over while the gas pedal was pressed... will this make a difference in compression numbers? Are my numbers inacurrate?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by r4integra &raquo;</TD></TR><TR><TD CLASS="quote">When I did mine, i got 225-230 across all four cyclinders, however the next day I couldn't remember if I turned the engine over while the gas pedal was pressed... will this make a difference in compression numbers? Are my numbers inacurrate?</TD></TR></TABLE>

You may still get the same numbers but it will take more cranks to get to since the throttle body isnt fully opened allowing air to easily get into each cylinder.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VTECorona &raquo;</TD></TR><TR><TD CLASS="quote">

How do you figure? Do you know what makes compression possible?

Let me fill you in on what valves do. Ok as the piston goes up, depending on what stroke its on, close or open. If it is on the compression stroke then all valves close creating a seal in the cylinder. If valves are not to spec, they will not create a perfect seal, thus not creating max compression. If you don't know what you're talking about, don't comment and make people believe false info.</TD></TR></TABLE>

okie mr know it all so .3 or more mm off make a really big huge diffrence.. i guess my machine shop guys are big liars then

 

your valves would have to REALLYYYYYY be out of spec to keep a valve open when its not supposed to be.

 

It will affect the numbers, whether it be 1 or 5 psi, chief.

I guess you go to a half-*** machine shop if they don't know that out of spec valve clearances can lower compression.


Modified by VTECorona at 7:12 PM 10/6/2003

 

On a stock gsr, how do you know what compression it's supposely be at?

 

It says in service manuals. I believe it is 270 stock.