Vacuum Port / Nipple on SC Intake Manifold

[jirwin]

What is this nipple for? I capped it originally thinking it was vacuum, but after it flew off it was obvious that it was on the boost side... so of course it would fly off. What is it for? Should I block it off with something a bit tighter?

 

[Sluggonaut]

My donor's boost gauge was connected to that port, so I have a hose on it.

 

[jirwin]

I figured that's what it was for... Time to add a Boost Buddy!

 

[Rauq]

It is a good source for boost source but it also drives the supercharger bypass valve.

 

[jirwin]

Care to elaborate? I thought that the bypass valve only connects to the port right next to it on the SC

 

[devianteng]

That nipple on the intake connects to the boost control solenoid, which is connected to the supercharger bypass valve.

I found this forum post which has relevant info, so take a look through it:

06 SS/SC Vacuum Line routing

I am in the process of troubleshooting a bit of performance and I think I have narrowed it down to the vacuum lines. When I got the donor the lines were in rough shape and dry rotted. I think that when I replaced them I may have missed/swapped some lines. Does anyone have a good diagram/photo...

dfkitcar.com

 

[jirwin]

I was actually just reading that myself. What would happen if you just let the bottom port on the bypass valve just vent to open air? That's what I'm doing right now because I have a 2.2L I'm supercharging and therefore don't have the solenoid

 

[devianteng]

I was actually just reading that myself. What would happen if you just let the bottom port on the bypass valve just vent to open air? That's what I'm doing right now because I have a 2.2L I'm supercharging and therefore don't have the solenoid

Sorry, I'm honestly not sure. However, I suspect that you could plumb the boost reference from the intake manifold to the bottom side of the supercharger bypass valve, and plumb the top side of the bypass valve to the nipple on the supercharger right by the valve. It's effectively setup the same way, just would be by passing the solenoid that the LSJ has. Since you don't have the solenoid, I don't see why this wouldn't work (and is the setup I would try).

 

[Rauq]

The solenoid is only there to give the LSJ's PCM the ability to dump boost if it needs to protect the engine. Since you don't have it, that nipple will need to go to the bottom port on the bypass valve actuator.

If I recall correctly, that diaphragm actuator is spring biased towards the bottom, or bypass valve opened position. When the throttle body is closed, both sides of the diaphragm actuator see comparable vacuum. When the throttle body is opened, the top side sees ambient air pressure, while the bottom side sees positive pressure, which reverses the position of the diaphragm actuator and closes the bypass valve so all the boost you're making gets stuffed into the engine. I would guess that without that bottom port you're not actually closing the bypass valve, so you're not getting to use all the boost you're making.

Then again, I have to re-figure out the bypass valve functionality every time I think about it, so I could be off the mark.

 

[r3drckt]

I'm doing an LSJ turbo swap and ZZP said I could use that nipple on the intake to run the BRFP regulator if you plan on running something like that as well.