I_am_imprezed

Cyl 1 152
Cyl 2 150
Cyl 3 150
Cyl 4 148

Is this normal for an 87 motor?

Van

I don't know... but I think that sounds about right.

I_am_imprezed

not very convincing, van lol

CameronB

I believe NA's run in the 170's and Turbos run in the 140's. Its also important that each of cylinders are close to one another.

-Cam

jcslocum

Lots of things have a bearing on these results, but even is most important. You have nice readings there. Is there any oil burn??

JohnKoaWood

10.3:1 if you were at 14.7 mean seal level... altitude, temperature and humidity will change them some, as will engine temperature and age of the oil in the engine.. you are close to spot on N/A high compression motor.. (10.5:1 IIRC), my guess is you took the measurements on a cold motor, on a hot day, or didn't block open the throttle body?

I can verify on my N/A once I get my compression tester back.... FWIW, there are MANY variables that affect the compression readings, it is MORE important IMHO that the readings are close together than what the actual readings were on any given day...

for instance I KNEW my #3 was weak in my turbo motor... and when oil consumption (among other things) became un-acceptable, I pulled the motor to have it rebuilt... IIRC #3 was 11% off the others, with #4 not far behind... when the motor was torn down, #3 piston rings were the worst, followed by #4... over all the numbers were OK, but the two lows, and #3 being more than 10% different told me if it were going to fail completely #3 would be the first to go!

ZW 944

After doing the head gasket I got very close to straight 165's with none over 165.

I have heard that 145+ is acceptable, and below that would be "poor"

Jeremy Himsel

When performing compression tests the peak number is not as important as balance. There are too many factors that affect the "number" such as starter speed, number of compression strokes, battery voltage, throttle position, gauge varation (there is a 15 psi difference between my craftsman and snap on compression gauges), carbon build up, dry vs. wet testing, engine temperature, etc. The results tell me this motor doesn't have any major problems (shot ring, bent valve, blown HG). I consider anything less then a 5% difference very good.

If you really have concerns about the health of your CC then do a leakdown.

JohnKoaWood

145 across all the cylinders would be fantastic, at mile high stadium, or anywhere else with LOW barometric pressure... remember compression is relative to ambient if you START wi 10PSI absolute in the cylinder 10.5:1 would yield exactly 105... but the engine wouldn't run... too low...

http://www.pelicanparts.com/techarti..._rebuild-2.htm

includes correction values for altitude... a low front moving in can vary the barometric pressure on any given day, even in some places multiple times a day...

JohnKoaWood

FWIW, OP lists Hudson Valley NY as his location, the valley itself runs from sea level, to just over 4200 feet in altitude...

If I were to take a guess, I would guess OP is somewhere near Poughkeepsie if not closer to the coast...

HAHAHAHA, I just looked at the OPs profile... Ellenville isn't too far from Poughkeepsie

Now how did I do that? 150/165 = .91 ... or roughly 3500 feet in altitude (correction factor from linked page)... Google Poughkeepsie topographical map, and you will see it is roughly 3500 feet in altitude...

OP, no worries, you are just higher than sea level... drive it closer to the coast if you don't believe me... repeat the test and report back what the new readings are... OR just trust you are good...

I_am_imprezed

The measurements were on a warm motor, warm but certainly not hot. Humid (poured 20mins after the test) and the throttle was wide open (injectors unplugged, plugs pulled).

There is oil burning on the track which is why i think oil is getting past the rings.

Jeremy - What does a leakdown test show you that a compression test does not?

JohnK- well done sir lol

John_AZ

When you did the compression test, did you pull the DME/fuel pump relay to avoid washing the cylinder walls and get an incorrect compression reading?

John

333pg333

Are you talking eye to eye with this mean seal though? Watch out, they bite!

When discussing the balance, what sort of variance is acceptable? Sounds like the OPs are pretty close to me.

jcslocum

I'm sorry to have to rain on your calculation parade but your elevations are quite a bit off. Poughkeepsie isn't 3500 ft above sea level. I live nearby in the valley and this is the listing for Dutchess Cty Airport:

Latitude: 41° 37' 36" N - Longitude: 73° 53' 3" W
Elevation: 49 metres (162 feet)

Ellenville Airport is listed as 292 ft.

JohnKoaWood

HAHA, I stand corrected... doesn't change the factors affecting his compression test results, nor the variation for environmental affects... values are not as important as variation across cylinders and IIRC the standard deviation is no more than 10%... but again, I could be wrong... f'n bike route maps and valley girls...