im not sure about your roush setup, but my non-ic has a vacuum line capped off coming out of the rear of the manifold. in the installation instructions, i believe it said that this was a place for mounting a boost guage.
now that being said, i installed my boost guage to the line and i dont get correct readings on my guage. at idle it reads a big vacuum and just gets to 0 or 1 psi of boost at WOT. it also shows a decent vacuum even when the motor is off, which im not sure is normal or not. i dont know if this is because of the line being incorrect or just a faulty guage. i think i remember trying a different vacuum line and getting the same results. maybe someone else with a roush will chime in...
dont drill any holes though, that guy didnt know what he was talking about...
oh by the way, are these the guages you have?
