Need advice reg. Comp. leak down test.

[runehar]

Hi, i consider buying a 1990 911 C2. milage 116500

I asked for a compression leak down test for it, and the seller replied

"A compression leak down test was done on the car before I bought it. The results were a low of 6% and a high of 20% in one cylinder. The mechanic said that he thought that one cylinder was high because the car had not been driven much of late and that the numbers would get better if the car was used regularly (it went for several months without being driven before I bought it). I asked him what kind of life expectancy the engine had left and he said that in his professional opinion that the motor should last another 50K miles before anything major needs to be done. The car runs and drives great and I would not hesitate to drive in anywhere"

I don't know much about this, and would really appreciate an opinion from someone who knows... How bad is high 20%?
I understand that the engine will need a top end rebuild, but it would be interested get an opinion on how much longer it will last. What cost's am i looking at... (i'm thinking about doing the mechanic part of the overhaul my self)...

Thanks guys.

Rune H.

[Dueller]

try this link;

Acceptable Compression & Leak Down Ranges?

[2.7RACER]

Rune,
A leak down test is designed to do 2 things.
One: Get a relative reading of the amount of air that passes through the cylinder at TDC compression.
Two: Determine where the air is going if a higher percentage of air is flowing through a cylinder.
Knowing that a cylinder is passing 20% of the air is half the test.
The other half is where did the air go? valves, rings, leaky head.
A simple compression test will show a low cylinder.
A leak down is used to show why.