Whats a good pressure in a healthy engine?

[Egz]

So, after decades working on modern cars, I finally get to go back to my roots. 1967 1600, trying to get some measurements to assess its overall health to decide how far to peel back the engine.

Just ran a compression test, cold, all plugs out, gas pedal down, and while the numbers were consistent, they feel low.
115, 110, 112, 95

Now, what I do know, the carbs are out of tune, and the exhaust manifold has a leak, valve lash probably could also be adjusted. She feels healthy, or maybe I just had low exceptions for her power output.

I wasn't really planning on adjusting the carbs until after I tear it apart and put it back together (don't plan on driving much beforehand). I could do the valves if you think that could be the cause of the low compression.

So, are those numbers low? I've seen people post around 130-150. What do you guys feel from experience?

Thanks

[jonny8]

I have a 1966 1600 and I got 140, 140, 140, 125 - mine feels strong - but in very much need of a tune up & balance to get it to run smoothly....

[notoptoy]

Was this engine running prior to testing? If it hasn't been running for a long time, then I would not read too much into the numbers. If it has been running and is able to be warmed up - then I would trust the numbers and think they are a bit low. I had always been told that a difference of 10% or more between any cylinders should be investigated, so I would be suspect of the 95 reading. Definitely try adjusting the valves and remeasure, it can't hurt. The next thing to do is to squirt a shot of oil into each cylinder and test again and see what the difference is. This will help point to rings versus valves.

[Egz]

It was cold. I can attempt to test again with the engine warm later.

With SUs, still leave the gas pedal down, right?

[notoptoy]

Definitely, the throttle plates should be wide open.

[Egz]

Warmed it up to about 150, and the numbers went up, slightly.

120,115,115,100

[redroadster]

You want a cold not run engine . or else the piston tops which go to 450- 900 degres are artificially bolstering readings
.every manu does. ...an important part is 1st pump. It should be 45% of specs
hows the blow by

[Egz]

Well the first set of test were cold. Just seemed really low. Would worn rings be a cause? I guess I should do a leakdown test (ack, means I have to get my compressor running)

Also attempted to check the timing. There seems to be no timing indicator by the crank. Just a cast rib in the timing cover. Am I supposed to use that? (if so, its waaay off)

[spl310]

The rib is the timing mark.

[theunz]

Reread notoptoy’s above to answer the question about the rings.

[C.Costine]

Re-read notoptoy's post and test wet vs. dry to determine rings vs. valves.

[Egz]

Roger. I'll try that later today after work, and on an unrelated note, play with the timing related to the rib.

[MattC]

Seems like timing could be important.

[Egz]

Well cam timing, I agree. I was just messing with ignition timing.

I suppose I should pull the valve cover off soon and verify that

[Daryl Smith]

Completely different, because both engines I've built for a little bit higher performance.
I shoot for around 185 psi cranking compression @ ~9.5:1 static compression.

Cam timing can have an effect on cranking pressures, but, doesn't seem to be the case here.
Ignition timing for the test is not a factor in any way.

For a stock fresh engine, well built, I would expect somewhere in 150-170 psi cranking pressure range? (haven't/won't build a stock engine)
I don't worry much whether the engine is warm or cold.
I test this way:
All spark plugs out.
Throttle wide open.
crank over till max pressure reached - usually 5-8 cranks.

@ about 120 psi you are probably about the low end of where the engine should be, but, if it still runs well and is not burning oil, I wouldn't worry too much.