what you think about my compression readings?

[weider1717]

Bought new plugs figured I would check the compression on my 87 only got half of them and my battery died and didn't charge and it's a new battery…anyway here they are. 87 350 5.7 69K miles.

BTW these were taken by my OTC compression test gauge supposed to be a nice unit so I assume readings are accurate.

cylinder #1- 172.5, 2nd test 174

cylinder #3- 175, 2nd test 175

cylinder #5- 175, 2nd test 179

cylinder #7- 180, 2nd test 180


Plug #7 the back one was a bit oily black wet other 3 were dry and looks pretty good. First test I have done been wanting to try out my test set any input on these readings? good? bad? so so? Also what should they be?

[enaberif]

What happened to 2,4,6, and 8? How did you do the test?

[weider1717]

Originally Posted by enaberif

What happened to 2,4,6, and 8? How did you do the test?

Battery died.

how i performed test:

I took the wire off the coil, unclipped the 2 fuel injectors. I did notice when I at first started to position the linkage back/open I created a bit of vacuum and I ended up not doing that but it looks to have slightly made a vacuum and the butterflies on the TBI setup aren't fully closed.

besides that removed the plugs and cranked it over 6 turns and took the reading then repeated.

I read most are like 120? mine is 180ish?? confused on this which is why I made this thread.

[68c10owner]

Originally Posted by weider1717

Battery died.

how i performed test:

I took the wire off the coil, unclipped the 2 fuel injectors. I did notice when I at first started to position the linkage back/open I created a bit of vacuum and I ended up not doing that but it looks to have slightly made a vacuum and the butterflies on the TBI setup aren't fully closed.

besides that removed the plugs and cranked it over 6 turns and took the reading then repeated.

I read most are like 120? mine is 180ish?? confused on this which is why I made this thread.

Was the engine hot or cold? That will make a difference. And you want the throttle at WOT when performing the test.

[weider1717]

Originally Posted by 68c10owner

Was the engine hot or cold? That will make a difference. And you want the throttle at WOT when performing the test.

I started it up moved it to me shop ran probably 5min I'd say by time I got the last of the 4 out it was not hot by any means.

are you saying to stomp the throttle as I turn it over?

[68c10owner]

Originally Posted by weider1717

I started it up moved it to me shop ran probably 5min I'd say by time I got the last of the 4 out it was not hot by any means.

are you saying to stomp the throttle as I turn it over?

To do tje test correctly the throttle has to be fully open. Engine temp will effect readings.

[MountainGoat1966]

You must be close to sea level to get compression that high from a stock engine.
Where I live, we get around 120 or so due to the elevation. Go to Phoenix and you can get as high as 150.

[weider1717]

Originally Posted by MountainGoat1966

You must be close to sea level to get compression that high from a stock engine.
Where I live, we get around 120 or so due to the elevation. Go to Phoenix and you can get as high as 150.

I am in upstate SC.

[lilpoindexter]

they are all fairly close to each other, so I think everything is all good

[school boy]

The main thing is all the readings are in a close margin of each other. If the other 4 cylinders are in that range, I would be happy with it. You will prolly have to perform all the readings again when you test 2,4,6 and 8 since the engine was slightly warm on the first test.