Misfire and Weird Compression Test

[turbo6cyl]

Hey everyone, I am a long time reader of this forum (lot of good info!) but posting for the first time as I am a little confused by my car currently.

I have a 1989 325i that I turbocharged myself last year and last summer all was well, made about 280whp at 13 psi for most of the summer.

This winter I oringed the block, changed the HG (Elring), and put in a 284/280 (Ireland Engineering) cam as I want to get closer to the 400whp mark. After putting it all back together, firing it up, and making some Megasquirt tuning changes for the new cam, I feel like the car has a misfire at idle around 8-900rpm. It does not have a completely clean lumpy idle like I would expect, seems like it misses here and there. I do not notice this past like 1200 rpm or so and there is no hesitation to rev or anything else weird. I decided to do a compression test after checking the spark plugs, wires, distributor etc. and finding nothing. I got about 9 bar of pressure on cylinders 1,2,4,5,6 and 11 bar on cylinder 3.....I know the factory spec is 10-11 bar and it had prefect compression on all cylinders at the beginning of winter before it all came apart. I am assuming the lower compression result now is due to my longer duration cam but why do I have such a different and high number in cylinder 3? I checked my cam timing and it was correct. Could the difference in compression be related to the misfire I think I am hearing? Any idea what the correct compression test pressure should be with a 284/280 cam and why there is such a difference with 1 cylinder?

I have not taken the car for a drive yet this year, just idling in the driveway really because I am trying to understand what is going on.

[ForcedFirebird]

Check valve lash just in case.

BUT. With a 272 cam, I see 145-ish psi (10bar), with a fresh Spec e30 engine, I see 185psi (12.7bar). Tired stock engines are about 145-150, good used engine will be in the upper 160's. Your compression numbers on the 5 cylinders is normal IMO with stock compression and larger cam.

Drop some oil in each cylinder before testing and see if they start to match #3, you might have an oil leak (likely valve seal) that's oil-sealing the rings for the test (will be more pronounced when cold).

[turbo6cyl]

Ok glad to hear you see around 145 psi with a 272 cam. I had no idea a fresh engine would see such high compression numbers! I had around 155 psi across all cylinders last year before I pulled it apart which doesn't seem bad considering the engine has 400,000 kms on it. I checked the valve lash multiple times too and its right around 0.010-0.011" for all valves. I will do the test again with a little oil in the lower cylinders and see what happens. A leaking valve seal never occurred to me as I changed them about 2 years ago but worth a look for sure.