MX-3.com

I picked up and will shortly hook up a boost guage on the X and it got me thinking, when I tap into a vacuum line, it'll let me know if it's under negative and positive pressure, but what happens when it's under positive pressure, what happens to stuff like the cruise, brake booster, and even the VRIS system on an Mx-3 when it's under boost? Those devices function by using the vacuum of the motor, but if the guage is telling me there's a postive pressure, wouldn't that mean that they wouldn't work? Wouldn't the vacuum lines pop off from the pressure?

Your brake booster should have an inline check valve and be ok. I put zip ties on all my vac hose connections to help them not pop off. Not sure on the cruise. I would guess that having the VRIS system close (as it would be with boost pressure pushing on the cam that activates it) would be of benifiet to keep the runners short under boost.

The VRIS system uses a check valve too. But yea I've wondered that too, wouldn't the cruise control not work then?

Nd4SpdSe wrote:I picked up and will shortly hook up a boost guage on the X and it got me thinking, when I tap into a vacuum line, it'll let me know if it's under negative and positive pressure, but what happens when it's under positive pressure, what happens to stuff like the cruise, brake booster, and even the VRIS system on an Mx-3 when it's under boost? Those devices function by using the vacuum of the motor, but if the guage is telling me there's a postive pressure, wouldn't that mean that they wouldn't work? Wouldn't the vacuum lines pop off from the pressure?

Check valves should cover most of the bases, and for cruise control it shouldn't matter since you'll never be WOT (so manifold pressure will always be negative relative to atmosphere).

True. So then pretty much everything vacuum related isn't meant to work at WOT, that's pretty cool.

Well, except VRIS, hence the vacuum chambers.