Sorry to stray off topic for something somewhat trivial but very basic for understanding turbo systems:

"With Mass Flow and Manifold Pressure, we are nearly ready to plot the data on the compressor map. The next step is to determine how much pressure loss exists between the compressor and the manifold. The best way to do this is to measure the pressure drop with a data acquisition system, but many times that is not practical.

Depending upon flow rate, charge air cooler characteristics, piping size, number/quality of the bends, throttle body restriction, etc., the plumbing pressure drop can be estimated. This can be 1 psi or less for a very well designed system. On certain restrictive OEM setups, especially those that have now higher-than-stock airflow levels, the pressure drop can be 4 psi or greater.

For our examples we will assume that there is a 2 psi loss. So to determine the Compressor Discharge Pressure (P2c), 2 psi will be added to the manifold pressure calculated above."

Quoted from:
TurboByGarrett.com - Turbo Tech103

^Compressor discharge pressure will always be higher than intake manifold pressure because of pressure losses in the piping leading to the plenum, especially through an intercooler.

The real issue here though is pointing out that the compressor outlet will see a change in pressure before a change is seen at the intake manifold; making the boost reference off the compressor outlet/discharge more responsive to changes in boost and help control any spikes that could occur from the wastegate signal being delayed.

"Best" is relative. If you want to run "x" psi(measured at the intake manifold) regardless of pressure loss across the intercooler etc, a boost reference off the intake plenum will do that. If you want the wastegate to respond quickly to any changes in boost, the shortest path/distance from the compressor outlet to the wastegate will do that.

this is a very true comment but it doesnt reflect how the boost travels. pressure drop and boost spike are two very different things. a well built intercooled system should only drop boost pressure by .5 psi or less. the pressure drop and boost spike will always be there but the boost spike can be minimized. im talking about the small period of time it takes for the boost to travel from the intake to the compressor housing causing a spike in boost pressure due to delayed wastegate opening. this issue usually only comes up when the engine is at a high load. a wastegate boost reference at the intake manifold is more accurate. ive been doing it this way for many years and many builds and never had a boost spike issue.

Agree to disagree :)

i guess so..... :)

Hey busa.. you still around?

If so, what did you do for fuel pressure regulator on your build?

I have a racetronix pump that can support the power and 63lb injectors. But they state I need to have a rising rate regulator? Is my OE one rising rate?