930 Turbo compression test numbers?
 

Doing a compression test on a 930 Turbo when the engine is cold, what type of numbers in pounds PSI should I expect? If doing the test on a twin plug setup should all twelve plugs be removed or is just six ok?

I don't know the pressure numbers for a 930, but I think you should do it when the engine is warm and the pedal is fully depressed.

Removing both plugs doesn't make sense since you will have a big hole for the pressure to escape when you do your test?

Tony
'78 911

I had my single plug 79 930 checked out before purchase. The readings were about 150 on each cylinder and I was told my mechanic that these were very good numbers.

Keith
79 930

The engine in my car internally is a mystery. The car has been highly modified and I don’t have any paperwork for the mods. When I purchased the car it had decals on the intercooler that indicated it was a 3.6 liter. Now the engine is a 3.4 liter so it may be punched out to a 3.6?

When I ran the compression test with the engine cold I got readings of 95-100 PSI. Should I be concerned with these numbers?

The previous post is correct, warm as possible engine, pull All spark plugs, throttle valve full open. On a Turbo I would pull both fuel pump relays so you don't pump that expensive gas all over. If the reading were all within 5# or 10# or so I would be happy since you did the test cold. As long as the engine is not using lots of oil or smoking then I would drive it since many items can affect compression such as a wilder than stock cam with more overlap will cause compression to be lower, etc.

Thanks everyone for the information and advice.

A leak down test will tell you the condition of your rings and valves alot better than a compression test.I have a supercharged big block in a 57 chevy and a leak down is all I can do to that.Because the supercharger still pump's air into the engine as you turn it over giving a false reading. Not the case with a turbo but it will pin point the problem if you have one.