Compression testing is invaluable in detecting variances and anomalies in
one's own car and of little value in comparing from car to car and technique
to technique - let alone the variances in the accuracy of the different
The following factors (and a few I haven't thought of) will provide
* How proficient is the unit at sealing the plug hole?
* How good a shape is the car's starter and battery?
* Is it a modern gear-reduction starter?
* Have all the spark plugs been removed, or just the cylinder being
* How warm is the engine, how recently run?
What is important is the relative readings on the cylinders on your car. To
get a smooth idle and to run well, it is easier if all the cylinders read
within 10-15% of each other.
When I got my TR4 a few years ago, I had a terrible idle and low compression
in #1. It took a while to discover it was the wrong valve guide (too big
Easy enough to drift out and replace - my, what a difference.
On another topic, one art we seem to have largely lost is the reading of a
vacuum gauge on a running engine. It can reveal an amazing amount about the
engine's overall health and flag specific faults.
Take a look at the scenarios here:
1962 Triumph TR4
Valley Forge PA.
Suggested annual donation $11.47