Compression Test Values - Factory Specifications?

[kharn83]

Hi Guys,

I just got my car compression tested because I saw white smoke coming out the exhaust once or twice, issue seems to be resolved but I got a compression and leak test anyway.

Compression test came back 193, 197, 208, 198 (PSI)

Leak down returned less than <5% across all cylinders..

Just wondering if anyone knows what are the factory specified compression values?

E.g. New from factory = 210-230 PSI range,
Engine in serviceable condition = ... 170PSI+?

Thanks in advance guys
Rob

[celek]

Previous engines I have had at 12.3:1 were around 210-215 and that was after 60k Miles. I would expect some issues at sub 200 on an engine with less mileage.

[stugray]

Funny that atmospheric pressure at sea level is ~15 PSI.
CR of 12.5 means 15 X 12.5 = 187.5 PSI.

That should be the highest static pressure you can get unless cranking the engine with the starter gives you a dynamic CR higher than 12.5 (not likely).

[celek]

Originally Posted by stugray

Funny that atmospheric pressure at sea level is ~15 PSI.
CR of 12.5 means 15 X 12.5 = 187.5 PSI.

That should be the highest static pressure you can get unless cranking the engine with the starter gives you a dynamic CR higher than 12.5 (not likely).

Or my $15 compression gauge from Autozone is not accurate

[murdoc]

Originally Posted by stugray

Funny that atmospheric pressure at sea level is ~15 PSI.
CR of 12.5 means 15 X 12.5 = 187.5 PSI.

That should be the highest static pressure you can get unless cranking the engine with the starter gives you a dynamic CR higher than 12.5 (not likely).

When I compression tested an s2000 my buddy was buying it came out around 220.

When you compress the air, it heats up, which further increases the pressure even more than just mechanically reducing the volume. The higher the compression ratio, the more heat adding to the pressure.

[200hp/tonne]

Originally Posted by stugray

CR of 12.5 means 15 X 12.5 = 187.5 PSI.

[Pedantic]Sea level 14.7. And TDC pressure equation is 14.7X(12.5^1.3x).
Although, since throttle bodies are closed and Engine is running at ~200RPM on the starter, it is tough to know the manifold absolute pressure without logging.[/Pedantic]

[celek]

Originally Posted by murdoc

When I compression tested an s2000 my buddy was buying it came out around 220.

When you compress the air, it heats up, which further increases the pressure even more than just mechanically reducing the volume. The higher the compression ratio, the more heat adding to the pressure.

I also compression tested my engine at Operating temp could also be a factor.

[cdrazic93]

Originally Posted by 200hp/tonne

[Pedantic][/Pedantic]

Totally unrelated but i cant pass it up, lol

[ame="http://m.youtube.com/watch?v=yetwdpsiM8Q"]http://m.youtube.com/watch?v=yetwdpsiM8Q[/ame]

[mav1178]

http://www.ft86club.com/forums/showthread.php?t=8374

[kharn83]

Originally Posted by mav1178

http://www.ft86club.com/forums/showthread.php?t=8374

Thanks, had a look at the engine manual couldn't find any references to comp test values.. I guess around 200psi is from factory new..

[BaBaFlyingSheep]

Originally Posted by kharn83

Thanks, had a look at the engine manual couldn't find any references to comp test values.. I guess around 200psi is from factory new..

So does anyone know what the values should be, with sources? Or is the 200 psi just from filtering the forum?

[mav1178]

Originally Posted by BaBaFlyingSheep

So does anyone know what the values should be, with sources? Or is the 200 psi just from filtering the forum?

Two posts above yours is a link to the FSM.

[mrspindlelegs]

Originally Posted by 200hp/tonne

[Pedantic]Sea level 14.7. And TDC pressure equation is 14.7X(12.5^1.3x).
Although, since throttle bodies are closed and Engine is running at ~200RPM on the starter, it is tough to know the manifold absolute pressure without logging.[/Pedantic]

Is that what the service manual calls for during the test on the twins? When I turned a wrench for a living back in the 1980s, the throttle was always set at wide-open during a compression test.

[BaBaFlyingSheep]

Originally Posted by mav1178

Two posts above yours is a link to the FSM.

Not in the FSM, that's basically what Kharn was saying in the post above. He looked thru it already.