FYI, I had an engine that had #3 cylinder at 85lbs the rest at 110/125/130. The car had a regular lope at idle and had problems passing smog. A compression test at fast idle could elevate the compresson to 120lb. What I finally discovered was a cracked exhaust valve. The weird part is that it didn't affect drivability as you would expect. At about 2100-2500rpms the crack would "seal" up and the hole would fire fine. The back pressure from the turbo helped to up the compression and "seal" the hole! Heck even at the smog tester the 25mph rating was fine though the idle was failing or nearly so. What is the moral of the story? A bad cylinder or headgasket can be sneakily disguised by the turbo pressure so that the car runs decently at mid rpm's. Another interesting fact to me is the turbos ability to quiet the exhaust noise. Turbos according to my muffler man do not have as loud an exhaust noise since they are converting more energy into heat and mechanical spinning than a normally aspirated car. I like the whine and whiz as i get on it. For turbos around 250-300K a head gasket and head cleaning might be considered regular maitenance.