I've heard and read various things regarding what is and isn't normal ranges for leak-down tests. Some sources say anything over 10% requires attention, others say over 30% is catastrophic and in need of rebuild, yet the tools used to perform such tests often show that 10-40% leak-down is considered 'low'. On the flipside, I have also heard that high duration camshafts and other variables can cause healthy engines to give readings of 30%+. In this particular instance also, a compression test showed nothing of concern and all cylinders were within 8psi of each other.
1. What else can cause leak-down test results to be 'high' in a healthy engine?
2. Can truly healthy engines produce high leak-down test results?
3. If high-duration camshafts can be the cause of high leak-down results, why do they cause this?
4. Are leak-down tests reliable measures of engine health for moderately worked engines? i.e. are the definitions of high and low results only relevant for standard cars?
Any definitive insight (rather than speculation) would be much appreciated.