Removing the Boost Return Hose

…Otherwise known as “How to make your G-60 sound like a taxiing F16 fighter jet.” 

This engine modification appealed to me conceptually.  It just sounded like it would be a good thing to do in order to improve performance.  As it turned out, “sounds” is a good word for this mod as it greatly increases the noises coming from the engine bay.  If you really like the “Whoooooooosh” sound that is made by some turbo cars when their blow-off valve lets loose, then you’ll love this mod.  If that drives you crazy, then you should stick with the stock configuration.


After the mod is complete


The VW 8 valve G60 motor has some interesting features to it that were added to accommodate the boost provided by the supercharger.  One of which is the boost return hose.  Basically there is a butterfly valve at the bottom of the throttle body that opens at times that full boost is not required (such as at half throttle or when you shift).  This valve opens in order to release boost so it doesn’t damage the intake system by hitting it with a huge build up of boost. 

The boost return hose runs from that valve to the back of the supercharger.  The boost that is bled off by the butterfly valve on the throttle body is fed back into the charger.  In addition to this, there is a valve cover bleeder that feeds into this tube to recycle the gasses that are released from the valve train. 

There isn’t anything particularly wrong with this setup except that it feeds hot air into the supercharger when the butterfly valve is open.  This somewhat negates all the work that is done by the cold air intake. 

 Supplies Needed:

Cypress Concepts makes a great kit to complete this mod in very little time.  Their web site is Cypress Designs.  The kit includes everything that you need except for tools.  You’ll need a few hex keys, a Phillips head screwdriver and a ¼” drive ratchet and sockets to remove some hose clamps. 

If you haven’t done the ISV reroute mod yet, you should do this at the same time. 

 Making the Mod:

It actually took me about 20 minutes to complete this modification.  There was very little disassembly required for this modification.  The instructions that come with the kit are pretty good.  I found that I only had to remove the boost hose going into the throttle body in order to access the boost return hose at the bottom of the throttle body.  It was a little tricky wiggling the hose out from all the wires and other things.  It took a little bit of a tug to get the boost return hose out of the charger. 

The kit maintains the breather hose connection to the back of the supercharger.  When you make the change, there is a tube that runs from the valve cover to the back of the charger where the boost return hose used to go in.  I took the “L” bend pipe out of the valve cover breather but kept the screw on cover to make sure that the breather fitting doesn’t pop off.  It also looks a lot cleaner.  Removing the heat sensor and “L” bend is easy enough.  There are 4 snap fittings that hold it into the plastic cover.  The cover then just screws back into valve cover. 

Valve Cover Breather close-up

L bend and heater fitting taken out of valve cover breather.


Close-up of the charger

The Results:

As I said, this mod adds a bit of noise to your motor.  If you use your car as a daily driver, or don’t have a stereo that is capable of drowning out a lot of whistling and whooshing, then you might want to skip this modification.  The motor is FREAKING LOUD!  At half throttle, there is a pretty constant whistling.  I’ve been told that this can be helped by adding about 6” of tubing to the bottom of the throttle body.  I’ll see if I can find something that will fit.  When you shift, there is a pronounced “PWWWSSSSSSSSSSHHHHHHHHH” sound that makes your motor sound like a turbo car.  It scared my wife a bit at first.  Now it just annoys her. 

I don’t have any dyno numbers on it yet.  The butt dyno has noticed a little difference in power.  I must say that I like all the whooshing noises.  I could probably do without the whistling.  I’ll see if adding some tube to the bottom of the throttle body helps that. 


Additional Mod:


After reading a lot about the Carbon Canister and how it loses its utility after many years, I decided that it was time to remove it.  This not only gets rid of about 10-15 pounds of stuff out of the front end of the car, but it also frees up some much needed space and makes the air intake area look much less cluttered.  Its also a great way to get rid of boost leaks.

It took very little time to do this and I’m very happy with the results.

There are quite a few vacuum tubes that go to the carbon canister.  Most of them can just be shortened and plugged. 

Two connections go from the throttle body to the carbon canister.  One is a small 3.5mm vacuum hose, the other is the large, 9mm size.  The 9mm one I plugged with a 10mm bolt and hose clamped it.  The 3.5mm vacuum fitting I used for my boost gauge.  I thought it might be good to measure boost right at the throttle body.  Both of these vacuum hoses had holes in them from wear and tear, so it was nice to get some of that boost back. 

Another 5mm vacuum hose runs from the left side of the “T” that comes off the intake manifold.  This I plugged with a 5mm bolt and zip ties. 

Vacuum tube "T" on the intake manifold

The hard line gas tank breather needs to stay.  You should not plug that.  I covered the end with a filter cloth and zip tied it down in the fender well where the carbon canister used to reside.  If you don’t do this, you’ll find that you get a lot of pressure build up in the gas tank.  If you don’t vent it down in the fender well, you can get gas fumes in the engine compartment. 

This is a great way to find and remove boost leaks.  After 13 years, my car was ready for some new vacuum hose.  I’ve still got a few more hoses to replace, but that will have to wait until later this week.   Its good to do this mod at the same time you do the boost return hose mod since you’ll have access to the throttle body at the same time. 


Good luck.  Drop me an e-mail if you’ve got questions.

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