I previously had a boosted D16z6 in my Civic. I just swapped in a JDM D15B w/ the same turbo setup.

Old oil pressure was like 20 at idle 30-40 at cruise and a bit more on highway.

New oil pressure is like 50-60 at cruising

Any idea why?

 

my b16 is right around what your new engine is.
usually as high as 75 at a cold start.

 

would running synthetic oil have anything to do with it?

Last time i used regular oil and this time im running full synthetic

 

The oil viscosity could have something to do with it and the basic fact that its a different engine. Even though the z6 and d15b share the same head, the block is still a little different.

 

Force = Pressure x Area .............. so basically pressure = area / force

Force = oil pump
Area = bearing clearances, oil galley sizes and so forth
So basically for your oil pressure to go up those things must have changed

Its a different engine Im assuming built differently