[Formulajones]

Chris at EFI System Pro actually recommends running a vacuum reference regulator on all the setups he sells. I found this out later.

I've always had a vacuum referenced regulator on both of our cars (Aeromotive 13301) for probably 20+ years with carbs, never ran a vacuum line to it though. Continued to use it the same way when the Holley EFI went on both cars and worked fine. Just swap out the spring for the EFI pressure and done.

Wasn't till about a year later talking to Chris about some tuning the subject of vacuum referenced regulators came up. He suggested running a vacuum line to it, as it lowers the fuel pressure at idle and light cruise situations and makes tuning those fuel tables much easier, more stable.

Even with the vacuum on the regulator, it still shows about 54-55 psi of fuel pressure at idle, and with more vacuum at light cruise it's about 52-53. So it's not a huge change anyway, but it did clean up those areas in the fuel table a pinch. Of course WOT vacuum drops and it jumps right to 60 PSI.