vacuum line between plenums

Quik LS

Registered User
I've hooked up my inlet/outlet plenums as much like a stock SC as possible.

I have a vacuum line that runs off a nipple on the input plenum to a nipple on the output plenum - basically in parallel to the bypass valve.


What does this do? Seems too small to offer a bypass failsafe.
Does it offer a little boost leak to prevent cavitation?

If you block it off - will you gain intake vacuum or outlet boost levels?


Thanks.
 
here it is....
 

Attachments

  • vacuum line (small).jpg
    vacuum line (small).jpg
    54.3 KB · Views: 226
  • vacuum line3.jpg
    vacuum line3.jpg
    279.9 KB · Views: 255
I belive it is to prevent cavitation. Back in the day people capped it off to create quicker boost. But no one proved it to provide any gains.
Just leave it on. It is there for a reason.

Post more your LS project looks like a nice set up
 
so would this cause pressure to build on the intake side of the SC when under boost and lifting up the pedal (closing the throttle plate)?

I guess I looking for possible issue with boost entering the vacuum line on the intake plenum - which normally would never see boost - things like brake boost, ...etc
 
I am no expert but it would make sense to me that there is so much vacuum being created from the blower that a little extra boost will not make a difference.
 
They call it the cross talk tube. If you search that u should find a bunch of stuff on it. Just leave it hooked up unless u need one of the ports for something else like alky injection.
 
Thanx - once I got the naming correct - there was a lot of good info.

I am using an 85mm TB and 3" intake tubing (haven't measured the MAF yet).

Since I am only running 4-5psi right now I'll measure how much psi I am loosing with that open and then block it off and see....
 
I tried blocking the cross talk tube about 5 years ago....all it did on my car was make the bypass valve ultra sensative to throttle input. The constant whine of the supercharger going up even the slightest incline got annoying real quick. Even though it is leaking air into the intake side of the supercharger, I couldn't tell a difference on the boost gauge or at the track, so I hooked it back up.

David
 
yeah - I read that in your past posts.

I've got two small issues:
1) seeping oil out the valve covers - like the oil refill neck, ...etc - nothing major but it look like I am pressurizing the more than stock... which makes sense (obiviously...). but I want to make sure I am not adding pressure where I should not be... so if it's all from the SC output - cool, if I am leaking boost into the intake and blowing pressure into a vaacuum line - bad...

2) I want to make more boost (slightly) than I am... I am running about 4psi. I want to run about 5-7psi - so before I order a smaller pulley I wanted to make sure I wasn't leaking boost out.

Did you gain any boost when you block it?
Did you gain any inlet vacuum when you block it?
 
There is a breather tube on the stock system that goes to the intake tube.
Do you have one installed? You could put a filter to allow the pressure to vent from the engine. Pressure in the engine is no good. Ours is on the driver side valve cover then the other side has the pcv valve.
 
yep - both valve covers vent directly into the intake. This model does not use a PCV system at all.

So I understand I'll 'suck' more oil into the intake that usual - because the draw will be more - but I want to make sure boost is not leaking into the intake where it should not be...
 
There will be no chance of the cross talk tube creating any pressure in the inlet plenum (between throttle body and blower inlet), because the blower is ingesting all the air it can suck in and the volume of air from the cross talk tube is rather small.

No I didn't see any change in boost or vacuum by capping it off. Others have reported slight increases in boost and performance, so you may want to give it a try.

David
 
I had the same question a couple weeks ago. Found out that the block on the return plenum with the vacuum nipples has a check valve in it.
 
do you remember which way the valve worked?

Does it leak boost into the intake or allow intake air to pass the by-pass?
 
Back
Top