Leak down or compression test?
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TECH Fanatic
Joined: Dec 2001
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From: Germantown, MD
Leak down or compression test? OK I'm not sure what the difference between these two tests are. From what I have gathered you plug into the park plug port and then turn the engine over a few times to see what each cylinder's leak down and/or compression is. What's the difference between these two test? how much to buy the components to do these tests and what info will they give me.
The reason i'm turning to these test is that I'm not seeing near 140 rwhp from my blower even though my gauges are telling me that the boost is there. Even with a very conservative tune I am expecting more power than i am seeing. For my SOTP meter i'm seeing maybe 40 rwhp gain from 8#s. Even with 18* timing at WOT I should be seeing more power than this.
So I want to verify that my engine is running in tip top shape. Which test do I need?
Thanks for the help,
Mike
The reason i'm turning to these test is that I'm not seeing near 140 rwhp from my blower even though my gauges are telling me that the boost is there. Even with a very conservative tune I am expecting more power than i am seeing. For my SOTP meter i'm seeing maybe 40 rwhp gain from 8#s. Even with 18* timing at WOT I should be seeing more power than this.
So I want to verify that my engine is running in tip top shape. Which test do I need?
Thanks for the help,
Mike
Re: Leak down or compression test? If you have a cam you will get a crappy cranking
compression number due to valve timing overlap.
A closed-valves leakdown test is a better
indicator of valve & piston ring integrity, fewer
variables involved. But you have to get each of
the cylinders' valves/piston to proper location
in turn, while for the cranking compression test
you just, well, crank it.
Actually, if the cylinder is in roughly-right
position the air pressure will probably move the piston to BDC for you. But you have to have the
valves closed and not have a cam where BDC makes
intake or exhaust start to open already. Otherwise
you're just as hosed as with the cranking test
unless you lock the flywheel in an everybody-
closed position.
compression number due to valve timing overlap.
A closed-valves leakdown test is a better
indicator of valve & piston ring integrity, fewer
variables involved. But you have to get each of
the cylinders' valves/piston to proper location
in turn, while for the cranking compression test
you just, well, crank it.
Actually, if the cylinder is in roughly-right
position the air pressure will probably move the piston to BDC for you. But you have to have the
valves closed and not have a cam where BDC makes
intake or exhaust start to open already. Otherwise
you're just as hosed as with the cranking test
unless you lock the flywheel in an everybody-
closed position.
