Turbo Inlet vacuum line cap?

[s4avant87]

Hi folks,

I purchased some rs4 style inlets from projectb5 and realized they don't have the vacuum lines that lead to the fuel rail. I've been instructed to cap off the hard line on the fuel rail side and forget about it. Anyone familiar with this? I've included a diagram to show what I'm referring to. Just want to make sure that while doing so I dont create an issue elsewhere.

Thanks in advance.

[belms4]

Unless I'm missing something, I don't see any functional point in capping those ends if you aren't using this line. All this is is a line direct between the turbo inlets on either side to help balance out pressure between the inlets just in front of the turbos. I guess you can cap the ends to keep dirt out in case you use the line again in the future, but capping the ends is safe and not going to change anything since you don't have these lines any longer.

Now whether or not this pressure balancing is needed or not is a whole different debate. I don't recall exact details, but I think depending on turbos it was kind of an extra. Might be some other threads out there on the topic if you want info on that and are rethinking your choice of inlets.

Sent from my SM-F721U1 using Audizine Forum mobile app

[s4avant87]

Unless I'm missing something, I don't see any functional point in capping those ends if you aren't using this line. All this is is a line direct between the turbo inlets on either side to help balance out pressure between the inlets just in front of the turbos. I guess you can cap the ends to keep dirt out in case you use the line again in the future, but capping the ends is safe and not going to change anything since you don't have these lines any longer.

Now whether or not this pressure balancing is needed or not is a whole different debate. I don't recall exact details, but I think depending on turbos it was kind of an extra. Might be some other threads out there on the topic if you want info on that and are rethinking your choice of inlets.

Sent from my SM-F721U1 using Audizine Forum mobile app

Good point. The thing that's making me second guess is the port in the center of the hard line (fuel rail) that leads to a check valve. It makes more sense to plug them to maintain that "pressure balancing" rather than let them vent to atmosphere but who knows. I'll give them a plug and hope for the best but at least the consensus is that those vacuum lines are somewhat useless.

Thank you.

[CELison]

You have to cap them. There's a third port in the center of the crossover rail. If you don't cap them you'll have a nice big vac leak.

[s4avant87]

You have to cap them. There's a third port in the center of the crossover rail. If you don't cap them you'll have a nice big vac leak.

Thank you for the follow up. I will be capping both banks.

[belms4]

You have to cap them. There's a third port in the center of the crossover rail. If you don't cap them you'll have a nice big vac leak.

Ah you are right! I totally forgot that one that runs down to the manifold was connected to these in the middle. Good catch.

Sent from my SM-F721U1 using Audizine Forum mobile app

[PwrWgn]

Those lines are the secondary vacuum source for the EVAP system. The primary source is the larger line that hooks up near the TB, which doesn't work when in boost. Your EVAP system will be degraded but i don't know if enough to cause a CEL.

[ss4]

Our 3” upper to 2.5” lower inlets do not have the EVAP ports either. You can tap into the intake tract somewhere to get “vacuum” when under load or boost. One side can be capped off for sure. On our Torque-Factory Y-pipe, we tap a fitting and run a small hose over to the rail for EVAP. And as said above, some people completely cap it off but we include fittings and caps to help the EVAP operate similar to factory.