I am getting a small amount of blow by from my breather filter. I have 1200 miles on my rebuilt forged motor. I was running a GST pump with stock injectors and a 12-1 FMU. The motor hasn't even seen 5 psi of boost yet that the waste gate is set to.

I did a compresion check on it and everything jumped right up 185. There is a small amount of oil on the first 2 threads of the spark plugs.

What could this be.

185 for a new rebuild..... that kinda seems low....

Sounds like your VC spark plug well gaskets are leaking..If you run around 8.8:1 compression, 185 psi is great. Thats exactly what i get for comression on my motor.

Could I have damaged the rings or cracked a piston and not have it affect the compreesion?

if:

1. you've run almost no boost
2. just rebuilt with forged internals
3. seated the rings properly
4. have 1200 miles
5. have 185 PSI of compression across all 4 cylinders

then your engine is running perfectly IMO. a little oil won't hurt anything. nothing seems broken to me at all.

what tempature did you do your compression test at? if the engine is cold the forged internals will not be up to tempature resulting in a little too big piston-to-bore clearance creating blowby, or "piston slap". sounds kind of like a diesel engine. everyone with a rebuilt 420A has this happen to them. it's not a problem at all.