acurateg96

i have a jdm gsr motor and finally got the compression checked on it. it read #1 239, #2 225, #3 211, and #4 207. my question is why would it be dropping in that order?

blinx9900

239 is extremely high but good none the less, are you sure you kept the throttle open for the last 2 tests cause there a lot lower... not sure why it would decrease in that order though, may just be a kawinky dink...

Scott_Tucker

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by acurateg96 &raquo;</TD></TR><TR><TD CLASS="quote">i have a jdm gsr motor and finally got the compression checked on it. it read #1 239, #2 225, #3 211, and #4 207. my question is why would it be dropping in that order?</TD></TR></TABLE>

Was the head resurfaced? If it was it is possible it was machined at an angle thus making the combustion chambers progressively small from one side of the block to the other.

coneheadsracing

Did you do the test? How many times was it cranked over for each test. After 5 or so, it'll keep building but slower.

s10cky

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

Was the head resurfaced? If it was it is possible it was machined at an angle thus making the combustion chambers progressively small from one side of the block to the other.</TD></TR></TABLE>

GOOD asumption.

turtleman321

also just from cranking it the battery looses power and doesnt have enough juice to pump cylinders 3 and 4 as much.

Scott_Tucker

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by turtleman321 &raquo;</TD></TR><TR><TD CLASS="quote">also just from cranking it the battery looses power and doesnt have enough juice to pump cylinders 3 and 4 as much.</TD></TR></TABLE>

I hope he didn't try to do a compression test with a dead battery. Even so in my experience it should not affect the test much even if the battery is partially discharged. Also, those numbers are pretty high which leads me to believe the head may have been milled.

The problem with the surfaced head may happen if they used one of those belt sander surfacers. Any bias in the weight put on the head will cause the surface to be slightly slanted. This could cause problems with the timing belt riding of the cam gear.

Vilt Innovations

those #s seem extremely high, even if heads where milled. you tested with oil in the cyls?

blinx9900

just for comparison my b16b checked in at 230 all across with stock 10.8 compression, i just think the first one is really high.

Scott_Tucker

You know, I've seen a lot of compression test numbers posted that are that high on here. They seem a bit high but if the engine isn't detonating it shouldn't be a problem. Especially since the purpose of the compression test is to compare the sealing of cylinders relative to each other.

acurateg96

how is it extremely high? arent gsr's supposed to be at 240? i took it to a mechanic to get the compression check and also a leak down test. all he said was i needed a valve job, get the head resufaced, and get the head gasket replaced. i havent done nothing to the motor internally. i just got the motor how it was from h motors