Mercury 1970 650cc Thunderbolt... 65hp<br /><br />1. 98psi<br />2. 95psi<br />3. 100psi<br />4. 94psi<br /><br />Or there abouts don't remember but it was within 6 foru sure.. Mechanic told me that the compression on a motor like this one is fine because older motors had much less compression...