got a compression tester to test the engine last weekend..

but toooo short to go into spark holes (screw in type tester)..

got extension for it to extend into holes...

extender has a internal bore of maybee 10mm (circa 1/2 inch) and is 200mm long (circa 9 inches) this bore is un valved...so the valve on the tester will have this space between the cylinder and the valve into which the compression can be 'absorbed'

I asume this will lead to lower than manufacturers spec readings, but - of course- the cyclinders should read approx the same readings...

can i work out a conversion formula..on the basis that

say engine compression is 8.5:1

take volume of engine/4 for vol per cylinder..

divide vol per cylinder/ engine compression to get % unswept volume...

multiply unswept volume % by cylinder volume to get unsept capacity

then add the capacity of the extension to the unswept capacity to get a 'measured' capacity...

then use a % against compression expected to get a target compression?

or something of that kind...

or is my thinking wrong here
...