Ian and I got his car running and its down to the fine tuning. We took it for a ride the other day and it is only making 5 pounds of boost max. Even with the MBC cranked, it only builds 5psi. Is it possible that if the timing is off the ECM wont let it build any boost? It should be at least 12 or so for the 16G. If it is the timing, does anyone know what color the wire it is that we need to ground for the timing? I know the wire comes from the harness coming thought the firewall by the battery, but after the wire tuck and fuse box relocate, we are having trouble finding the wire.

Thanks

First thing's first, eliminate the MBC. Run a line straight from the pressure source to the actuator. Or, disconnect it from the actuator and boost carefully to test.
You can also wire the wastegate shut if you think opening, and drop the O2 housing to see if the flapper is intact.

If you have a logger plugged in, it will lock the ISC instead of the timing. So you could do that to test. I think you should also see the timing locked on the logger.

A few other things come to mind: Boost leaks, exhaust leaks, clogged cat or plugged exhaust.

We tried it first without the MBC. It was the same as when we put it on. The turbo is brand new, so I cant see any issues, but dropping the O2 is possible to see if the flapper is opening. Will a vacuum leak actually effect it like that? We cranked the MBC, so it should have went to 25ish psi....and nothing. We will check the flapper, and then maybe disconnect the exhaust to make sure nothing is plugged. Other than low boost, the car runs awesome. Perfect air fuel, turbo spools well....everything is great. We found out that his maft is for an LS1....could that be the reason?

With a 16g actuator you should get atleast 7-9 psi with boost running straight to the wastegate. The base timing being too low or high will not cap your boost at 5psi, it should still spool higher than that.

You say the turbo is brand new ? Check for boost leaks or run with the line disconnected from the wastegate, as mentioned above to help you narrow it down.

Found the boost leak, problem solved. Tbolt clamp wasnt even close to tight on a coupler, not sure how we missed that. Still havent done base timing but car runs awesome otherwise still. Got it up over 20 psi easily now.