hi just done a compression test on my v8 5litre and they were all around 120 is that good or bad.?

Question

It's Holden vr Commodore.

Answer 1

It's not about the number that it is, considering it will be different for everybody, depending on the length of your reading hose, the size of your gauge, etc...(more volume means the piston would have to push further to get the same reading)

It's about consistancy. If all your cylinders are reading the same, you're off to a good start. Are you checking it hot? With a full battery? Antother thing you want to watch for is that each stroke is the same. If each successing stroke builds up more pressure, there's blow-by on the piston rings. If it's just lower than the rest, and it's consistent, it's either a blown head gasket or improperly seating valves.

Anyway, 120 sounds pretty good. That's actually really good. Doesn't sound like you've got any leaks to me. Are you having trouble? What are the symptoms, maybe I can help you.

Answer 2

Holden would be a Chevrolet equivalent in Australia. The 5.0 liter would be about the same displacement as a GM 305-307 cubic inch engine. 120 psi per cylinder is a little low. Ideally a reading of 150 is needed to keep the engine running in good shape. You may be at the point of wear that a rebuild is necessary.

Answer 3

Need the model of the car to determine what is the proper pressure.

From what you have given, if they are all 120 all around then it is wearing evenly, if 120 isnt the right pressure.

Doesnt sound like you have any problems unless you are losing serious power.

Answer 4

I suppose you are talking about a Ford? I would go for a leakdown test, that will tell you much more than a compression test.

Answer 5

if the compression is consistent on all cylenders then it's a good thing