I have my defi vaccum source taped on the line between the manifold and valve cover and it seems that my defi gauge is reading 3-4 psi higher then what the boost really is.

I'm running a aem ems and have a boost cutoff at 9.5 psi and my gauge reads like 11 or 12 psi all the time
also when the tuning was done we saw max of like 8psi

should i tapp into a different vaccum source and if so where would be the best to tap for the defi gauge and for the bov?

 

What's your altitude? Your Defi is reading relative boost pressure within the manifold. The AEM is reading absolute pressure relative to the atmosphere. The AEM will almost always read lower.

I am at over 5000ft ASL and my AEM reads quite a bit lower than my Defi unit.

 

so which one is correct and actual boost pressure I live in charlotte, NC i have no idea what its relative altitude is.

Also the defi unit on my buddies rsx seems to read correctly

 

Absolute pressure = Gauge pressure + Atmospheric pressure