420A 420a Low compression Not starting

[420a_zhen]

So I turbo my 420a full build pretty much. Put it all back together and it doesn't start. Checked compression and it has
20psi
160psi
100psi
50psi

Low in pretty much all cylinders. I have the weisco 8.8.1 pistons and the rings are all to spec, valves are all fine too so it has to be a timing issue right?
Don't know my next step so figured I'm ask here.

 

[BLACK'98DSM]

Yea start by checking your mechanical timing before digging into the engine. Did you have the head resurfaced and pressure checked by a machine shop? Valves lapped and new seals? Cylinders measured/honed? Hopefully you did not re-use head bolts as they're torque to yield, head studs are preferable for turbo application. Were the head bolts/studs torqued in the proper sequence to the proper torque spec?

There's plenty of things that could be wrong so you need to diagnose.

 

[CKOPOCT]

Whoa! With those numbers something is way wrong.

+1 to what @BLACK'98DSM said. Double check your timing marks (set to TDC, inspect cam and crank marks, spin by hand 2 full revolutions to fully cycle cams, then recheck marks to ensure all are still properly aligned). If things are good, recheck compression. Should be at least 150 per cylinder and pretty consistent across the board. If not, do a leakdown test to see where you are losing air.

 

[97egl]

Also make sure your lifters are bled down. If they are not collapsed enough they will hang the valves slightly open.

If there was machine work done to the head and they cut new valve seats but didn't set the valve installed height the valves could be getting hung open even when the lifters are fully collapsed