what makes copmression tests vary? Ive been doing a good number of tests lately since ive had a good bit of variation.

first off, motor is 84 mm gsr with 9.1:1 arias pistons- ringed at 18 top, 20 bottom (i think, what earl reccomended me) all the valve seats were recut when the motor was rebuilt (~1000 miles ago) Heads strapped down with arp head studs. thats about all i can think of that will change compression tests.

test one : 250 miles ago.... 180 175 175 180

test two : 100 miles ago.... 150 170 175 185

test three: 50 miles ago... 165 162 165 187

test four: currently... 167 175 175 180

test five: currently ( 5mins after the last) 160 180 170 185

After the test 100 miles ago i was obviously surprised the compression dropped 30 psi in one cynder. As of now i have no clue why. After seeing alot of variation, i figure maybe something was up with the gauge, so i got a brand new one, and the compression tests are still pretty random.

Any insight to this? Any thoughts on why compression would drop 30 psi in only one cylinder after 150 miles? (no over revs, no missed shifts, no change in tune, no over boosting.)

 

oh yea... tests always done with the ecu fuse out, wide open throttle, and no spark plugs in

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by adictionbass &raquo;</TD></TR><TR><TD CLASS="quote">oh yea... tests always done with the ecu fuse out, wide open throttle, and no spark plugs in </TD></TR></TABLE> Have you done a valve adjustment Latly?

 

was the engine warmed up first?

 

yes, the engine was always good and hot (wamed up, and driven at least 5-10 miles) before every test

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by OBRJosh &raquo;</TD></TR><TR><TD CLASS="quote"> Have you done a valve adjustment Latly?</TD></TR></TABLE>

i have not done a valve adjustment in the last 250 miles these tests were done.

 

well i'll have to ask, did you crank for the same amount of time on each cylinder?

i cant tell you how many times someone has thought they dropped compression because they didnt crank the right amount of time.

 

yes, i count the same every time, basically one mississippi two miss..... through 4. i crank it till the gauge stops going up.

 

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

i have not done a valve adjustment in the last 250 miles these tests were done.</TD></TR></TABLE> When was it done whent he motor was first built??? Did you do them or the builder did them, Cause my valvs were way off and it made a hugh change in compression when i did the valve adjustment, checkum out

 

def will do. I did it when the motor was first built (1000 miles ago). One about 200 miles after, and then one at about 500 miles.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by adictionbass &raquo;</TD></TR><TR><TD CLASS="quote">def will do. I did it when the motor was first built (1000 miles ago). One about 200 miles after, and then one at about 500 miles. </TD></TR></TABLE> Were they changing after that little bit of mileage???

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by adictionbass &raquo;</TD></TR><TR><TD CLASS="quote">def will do. I did it when the motor was first built (1000 miles ago). One about 200 miles after, and then one at about 500 miles. </TD></TR></TABLE> I was getting like 150-170 before the valve adjustment, after i did the valve adjustment went to 230-240 accros the board HAhA Mine ended up being way to tight and keeping the valves form closing all the way

 

however, i do know i have a good amount of blow by. There is a good amount of air comming out of the catchcan breather, and alot when you pull the oil cap off. (i understand that the little bit larger ring gap reccomended for turbo is the main cause of this correct?)

Ill give the valve adjustment a check and report back. (probably will have to wait till this weekend)

Still interested in other opinions/experiences

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by OBRJosh &raquo;</TD></TR><TR><TD CLASS="quote"> I was getting like 150-170 before the valve adjustment, after i did the valve adjustment went to 230-240 accros the board HAhA Mine ended up being way to tight and keeping the valves form closing all the way </TD></TR></TABLE>

damn, they must have been way off. Did you have any blow by at the time?

 

 

I just cant help but think its an issue with the piston rings.

 

I prefer a leakdown test.... its more accurate to guess the condition of a motor.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by OBRJosh &raquo;</TD></TR><TR><TD CLASS="quote"> I was getting like 150-170 before the valve adjustment, after i did the valve adjustment went to 230-240 accros the board HAhA Mine ended up being way to tight and keeping the valves form closing all the way </TD></TR></TABLE>

wait if the valves arent closing then you shouldnt have any compression right?

i am having this problem right now. I just did a valve adjustment to factory specs and my 9:1 motor is making 240 psi! wth!

 

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

wait if the valves arent closing then you shouldnt have any compression right?

i am having this problem right now. I just did a valve adjustment to factory specs and my 9:1 motor is making 240 psi! wth!</TD></TR></TABLE> They were set way to tight like .002 haha

 

I think I might do another compression test on my car tomorrow. From what I remember my test results yield varied #'s as well just like yours. I wander why as well?

 

the the valve adjustment. two vales were maybe .001 off from where i put them. Compression came out the same. Im going try to get a leakdown tester...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by adictionbass &raquo;</TD></TR><TR><TD CLASS="quote">the the valve adjustment. two vales were maybe .001 off from where i put them. Compression came out the same. Im going try to get a leakdown tester... </TD></TR></TABLE> Yea Leakdown time Good Luck