Does Type Intake Make a Difference In Comp Test Results?
Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,145
Likes: 1
From: Ft. Walton Beach, Fl USA
Does Type Intake Make a Difference In Comp Test Results?
I did a compression test in Oct 2008 and I did another last nite. I used the same gauge (Craftsman) and everything else was the same except this time the motor has a WP Motown single plane vs an Edlebrock RPM AirGap in the first test. The test results were about 20-25 difference (less) across the board with the single plane. Are these results normal?
Just for additional info I used two different gauges last nite and there was a consistant 15 psi difference between the 2 gauges. One was a generic (read higher) and a Craftsman. I'm leaning towards believing the Craftsman because the dial jumped significantly on the first revolution and only took 7-8 to max out. The generic was slow to respond initially and took up to 18 revolutions to max out.
Just for additional info I used two different gauges last nite and there was a consistant 15 psi difference between the 2 gauges. One was a generic (read higher) and a Craftsman. I'm leaning towards believing the Craftsman because the dial jumped significantly on the first revolution and only took 7-8 to max out. The generic was slow to respond initially and took up to 18 revolutions to max out.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
The intake style/type will make no difference at all- you could do the test with NO intake and see the same result, provided the carb was fully opened with the intake.
2 different gauges will give different readings- just due to calibration. On a compression test, the only things that really matter are what it gets to on the first stroke and the maximum. But it should only take 5 to 8 strokes to get there too. And look for no more than a 10% difference between high and low. If any 2 adjacent cylinders have EXACTLY the same readings from the first stroke to the max, that's a problem.
As far as your 20-25 psi difference, it could be anything from ambient air temp to humidity to engine temp, and lots of places in between.
2 different gauges will give different readings- just due to calibration. On a compression test, the only things that really matter are what it gets to on the first stroke and the maximum. But it should only take 5 to 8 strokes to get there too. And look for no more than a 10% difference between high and low. If any 2 adjacent cylinders have EXACTLY the same readings from the first stroke to the max, that's a problem.
As far as your 20-25 psi difference, it could be anything from ambient air temp to humidity to engine temp, and lots of places in between.
Thread Starter
Melting Slicks
Joined: Apr 2000
Posts: 2,145
Likes: 1
From: Ft. Walton Beach, Fl USA
The intake style/type will make no difference at all- you could do the test with NO intake and see the same result, provided the carb was fully opened with the intake.
2 different gauges will give different readings- just due to calibration. On a compression test, the only things that really matter are what it gets to on the first stroke and the maximum. But it should only take 5 to 8 strokes to get there too. And look for no more than a 10% difference between high and low. If any 2 adjacent cylinders have EXACTLY the same readings from the first stroke to the max, that's a problem.
As far as your 20-25 psi difference, it could be anything from ambient air temp to humidity to engine temp, and lots of places in between.
2 different gauges will give different readings- just due to calibration. On a compression test, the only things that really matter are what it gets to on the first stroke and the maximum. But it should only take 5 to 8 strokes to get there too. And look for no more than a 10% difference between high and low. If any 2 adjacent cylinders have EXACTLY the same readings from the first stroke to the max, that's a problem.
As far as your 20-25 psi difference, it could be anything from ambient air temp to humidity to engine temp, and lots of places in between.
