Compression test completed.... Question.
Thread Starter
Drifting
Joined: Jan 2000
Posts: 1,612
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From: Phoenix Arizona
Compression test completed.... Question.
I did a compression test when the motor was cold. All of the cylinders with this cam were approx 173-175psi... I then read tonight that it should be done when the motor is warm.
Will I see a big difference if I re-do the test after warming the motor up or should I take these numbers as "near" accurate?
Thanks!
Bob
Will I see a big difference if I re-do the test after warming the motor up or should I take these numbers as "near" accurate?
Thanks!
Bob
Le Mans Master
Joined: Oct 2004
Posts: 5,269
Likes: 54
From: Orlando Florida
St. Jude Donor '05
You'll see better compression when the engine is warm (at operating temperature) - the pistons and piston rings expand a little more than the block, resulting in tighter clearance and better sealing.
The pistons are different material than the block (aluminum vs cast iron in most cases), the pistons see more temperature, they're not water cooled like the block... somebody else may want to do the math on thermal expansion to get the exact numbers...
The pistons are different material than the block (aluminum vs cast iron in most cases), the pistons see more temperature, they're not water cooled like the block... somebody else may want to do the math on thermal expansion to get the exact numbers...
