I have a 2011 mustang gt M6 with a vortech si. I had a boost gauge line get semi melted so I changed it and I've noticed that on decel and idle the vacuum on my roush gauge read below 20 and I don't remember it going that low before does anyone else's go that low or is 20 the norm?

 

I regularly pulled 20" on my last supercharged 5.0...however, it had pushrods.

Anyway, the amount of vac your engine pulls isn't really important unless you aren't pulling any and your brake booster doesn't work. That can get scary.

As long as the gauge is zeroing properly, drive on.

 

Thanks good to know. I just got make sure and keep her healthy.

 

yeah, only be concerned if it starts to drop manifold vacuum precipitously, as that could be an indicator your engines on the way out.