I just checked the compression of my n14 r56s, and #4 is just out of tolerance, a touch over 11% difference between the highest and lowest numbers. I have no codes or misfires or issues, other than running a little lower boost than expected. The testing was done dry on a cold engine. Should I dig deeper or just wait til it gets worse? Could this be the reason for the less than expected boost? It’s really cold in the garage this time of year, it would be great to put this off for 6 months if possible.

1. 166, 170
2. 164, 168
3. 165, 170
4. 150, 150

 

Could try a walnut blast and see if that helps any, next step would be a new head gasket which would allow you to check the valves.

 

Just did a walnut blast in January, along with a new valve cover, catless dp, g-plus intercooler, new diverter valve, 1422 spark plugs, a few other misc things, and a rpm stage 2 tune. Also scoped and tested the wastegate to ensure it wasn’t leaking. And I pressure tested the intake to 25 psi without finding any external leaking. Trying to avoid pulling the head in the cold, I just don’t have the space to do it until I finish a shed in the spring, along with dropping the pan because it has slight seeping and needs a new gasket. Perhaps I’ll take the intake manifold back off and focus on the valve seats in 4 to make sure I didn’t miss anything.

 

If you did the test dry, and got those numbers, try it again wet (couple drops of oil in the cylinder) and see it the low number goes up. If the low number is now within range of the others, you have bad rings. If it stays the same, it’s valve related.

 

Ran a warm test before doing a wet test and the numbers show good. I guess its all fine? At operating temperature I'm within the right margins. Still searching for why I'm about 4-5psi boost below where ti should be.

1. 185
2. 176
3. 174
4. 175

 

What boost pressure are you getting and what pressure are you expecting?
Keep in mind that max boost can vary with the weather - seriously.

 

Mario tells me I should be seeing 21.5 psi of boost, even in this weather. I'm seeing max of just under 17 psi. It goes right to 15 psi pauses for a moment, then slowly builds from there to about 16.5 psi. I've ran out of things to check/doublecheck/triplecheck/etc.When it has been in the 20s F, I it sometimes will be slightly less than those numbers.

 

That is on a stock turbo? If you think about it, boost in some sense is a function of the RPM of the compressor wheel, the diameter and the sealing of the blow off valve, assuming you have a sealed path to the intake manifold.

Your cats could be plugged with old crud so you can't get enough flow for high RPMs. But still, 21.5 on a stock turbo?
Edit: just saw you have a catless DP, so scratch that.