Hi,

Got my spark plugs replaced so asked to check a compression, having this opportunity. Results are equal at each and every cylinder - 110psi.

Looks low comparing to NA engines, but 8 results being equal looks promising.

What are your thoughts? Bear in mind XKR - 5.0 supercharged 62k miles on a clock...

 

A forced induction engine will almost always have a lower compression ratio than the equivalent NA version coz the greater volume of fuel/air mix more than compensates for the lower compression. Dunno about diesels though I guess it would be the same.

 

road test time

 

Car runs very well (almost 600bhp on a dyno after tune). But did not run another 5.0 s/c, so lack of A/B to comparison.

 

If you look at the procedure in the repair manual, you'll note there is no 'nominal' pressure. This is due to the variation in testing equipment - specifically the length/diameter of the air hose being used, among other variables.

From the manual: "The indicated compression pressures are considered within specification if the lowest reading cylinder is within 75% of the highest reading."

By that definition, your engine is solid.

I guess the only real way to know is to use the same tester on another 5.0 S/C Jag engine and compare.

This might help:
http://www.healey6.com/Technical/Nom...20pressure.pdf

 

All within 10%=all is good

 

In my case they are within 0-5% range (as gauge is not super accurate) - but all of them had equal results.

So all in all - I take it as a healthy engine, no signs of extensive usage so far.