Can anyone explain to me what the purpose of the Bypass Valve is on the Supercharged V8's?

Here are the details from the parts catalog;



Two reasons why i'm asking;

1. It's mentioned in the Kenne Belle paper about low boost http://kennebell.net/KBWebsite/Commo...esAndCures.pdf

2. The junior at my local garage mentioned that adjusting this bypass is a means of getting more boost, not unlike the wastegate in a turbocharger.

I'd never heard or seen of anyone any adjustments in our cars, anybody know anything more about it?

 

From Eaton's Supercharger FAQ:

Q: What is this black plastic object on the side of my supercharger? What is a bypass valve?
A: That object is the bypass valve vacuum actuator. This unit has a vacuum port that connects to the supercharger inlet between the rotors and throttle body. This actuator opens and closes a bypass valve for the supercharger. This valve is open when throttle loads are low and closed when throttle loads are high. With the bypass valve open there is no pressure being created across the supercharger. This allows the supercharger to have an almost negligible parasitic loss in this condition. With the bypass valve closed, all airflow is routed through the supercharger and boost is created in the intake manifold. In some newer applications this actuator is also controlled by a solenoid.

 

Thank-you!

So in that case we need to be sure that this valve is completely closed on boost and that there are no leaks in the connecting pipes.

Another one for the to-do list.

 

yep pretty much all it is as explained above I wish it were like a wastegate haha. Make sure that the pipe connectors are nice and tight and the bypass closes all the way otherwise yes will get a boost leak

 

Hmm, so where does the air to when it bypasses?

 

When the bypass valve is open the air is recirculated from the supercharger outlet back into the supercharger inlet.

 

Help! I need a new Bypass valve for my XJR anyone know where to find one??

Rusty

 

Tried the forum/site sponsors?

 

Cambo- there is NO BENEFIT to not having the bypass valve on a positive displacement device like a Roots style blower (including the TVS).


This is because it does no internal compression work and merely supplies a volume. When it is bypassed- the parasitics are quite low- almost like a PAS pump or alternator. This doesn't apply to something like a lysholm compressor which does internal comp work and must be de-clutched to get rid of parasitics.


Unfortunately a lot of the internet/forum know-it-all try to boost 'part load' performance- and don't realise how stupid that is. If you want more performance - you put your foot down- to WOT if necessary, otherwise you may as well focus on lowering pumping losses.

 

I totally agree with this!

 

Whilst doing a smoke test on my 07 to find leaks I noticed a small one coming from the join of the actuator body. It opens on start up but obviously I don’t know it the leak is stopping it from closing under load, there’s plenty of power so I’m assuming it’s ok.
Whist I’m not keen on spending £160 on a new one I would like to fix it. I was thinking about thoroughly cleaning and preparing the surface before using Tiger Seal or Sikaflex PU adhesive to seal it. A few questions:
1. Does the actuator come apart
2. Would a small leak there cause any fault codes
3. Is the actuator removable without pulling the charge coolers, i.e. pulling the inlet tubes and T-piece on the throttle body

Edit: I may be answering my own question but further searching shows this o ring is available, at 4cm x 4cm x 0.2cm it’s about the right size.