Leakdown tests?
 

What kind of numbers do you get which show your rings are worn out and need replacement and/ or over bore?

What performance or horsepower loss has anyone seen?

Thanks, John B

Don't think you want more than 10% on any hole and if the rings are going, you should hear air through your breather holes.

HP Loss
 

John,
I believe you are right. My sources say's at 20% leak down on 4 cylinders you are down maybe 10 - 15 HP per engine. Although this isn't significant, it may be 1 MPH on your top end.
Sprague