I have an 87 900 SPG and well i got boost happy and decided to take the the wastegate out of play for a few mins and well frankly it ran fine and pulled like no other but the flapper for the wastegate lets pressure out so it didn't work as well as expected anyway so later that day i noticed at idle it was puffing smoke out of the oil fill tube and that ain't good so i checked all the compression ratios and all but #2 are up at around 10 1/2;#2 is at 6 3/4 not good eh? well is it rings my guess or what else could it be?

It can be a leaking valve. Sometimes, a little part of exhaust valve can detach from the valve and in compression phase, there is a leak to the exhaust. The best is to open the head.

Find a garage that has one of the testers that connects a controlled air line into the spark plug hole. Stand back and see where the air comes out.
My local garage has one, but that's not much use to you over there.
Fred

sounds like rings if it's coming out the dipstick hole.Had same prob on a 204k mile volvo-uneven compression readings and vapour coming out the dipstick hole.Took head off a wear ridges were like steps-one knackered engine!
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whats the miles on it?

it has 189,000 miles on it and it has the apc done to it,borla exhaust,msd blaster 2 coil, copper head gasket.

and about the exhaust valve i wish it were so but how would that leak compression into the oil chamber unless the seals went on it which is highly possible too. i did the head gasket about a month ago.thnks

sorry to be pessimistic but the only way I can see pressure going into the oil sump is via the rings.If one of the valves was leaking then it would either go down inlet manifold or into the exhaust.Maybe an idea to get that controlled air test done(drill a spark plug out and connect a compressor to it!) then u will be sure
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One of the problems with changing h/gasket on an older/high mileage engine is that the compression can be increased significantly if the valves are decoked.This puts a lot more strain on an otherwise worn bore.Funnily enough my engine only lasted a year after a decoke-the power increase was really noticeable tho'.
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even if your valve stem seals had gone it would be more likely that oil would get into the bore causing blue smoke.I don't think stem seals would affect compression readings.It's got high miles and it's turboed so my money would be on rings.
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I think you're right alex. Surely the rings. I was talking about exhaust valve but (Sorry 87SPGIN...) i didn't see that you were talking about smoke via oil dipstick.
So i revised my position.

Yeah unfortunately things don't last forever,everthing wears out.
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even if it's a saab!
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thanks all for your posts they help alot i went to the saab dealer near me and i actually got some info out of him (cool) he told me to do a wet compression test and so i did and came up that #'s 1 and 4 were outstanding 180 psi (i think thats the units)
but 2nd was 135 and 3rd was 145 which suprised me but anyway. i'm nto sure exactly what that tells me the 2nd cyl went up with the wet seal and 3rd did too which tells me prob not valve right?.....on going

When you do a compression test and the readings are low/uneven, you then do a wet test (squirt some oil in each cylinder) if the readings then rise, this points towards the rings, as the oil in the cylinder runs down the side of the pistons and provides additional sealing and therefore raised compressions!!
The other test that alex mentions is called a cylinder leakage test, putting compression into each cylinder and testing for any lost pressure, where the air leaks out is where the problem lies!!! ie exhaust would indecate valves, crankcase would be rings!!

those #2 and #3 cylinders are well down tho' definitely a problem there.On the volvo sometimes the idle speed would drop and u could see smoke coming out the dipstick-then the ring must have spun round slightly,the smoke stopped and idle speed went back up!-#1 piston was the most worn so i assume it was sometimes sealing sometimes not.The engine was carburettor so no injection to worry about.In the end the car would only do 80mph on the motorway so I knew something was wrong #1 cylinder had gone completely,loads of smoke out the dipstick hole/oil breather and used loads of oil!

yes all of my sources have pointed towards rings which is ok cuz while i am down in the dirt i had might as well redo the whole bottom end(JEforged pistons,new rod bearings and so on....) but that will require time and patience oh yeah and money too. the 2nd and 3rd cyl all went up with the wet test here are the figures:
dry wet dry(after wet)
#1 150 180 150
#2 90 115 90
#3 145 190 145
#4 145 190 145

All of which point to the inevitable rings well thkns all for ur help.