3

I would like to install a manometer (boost gauge) on a '97 Alfa Romeo GTV with a 2.0L V6 Turbo engine. Before messing with the engine, I picked up the its repair manual in order to better understand how the turbo/intake system worked and better choose where to place the manometer. These pages present the turbo/air system, and I have some questions about them:

  • I have noticed that this car does not make the loud whoosh sound we sometimes hear from turboed cars, is it because of the anti-stalling valve (tag 11 on the first diagram)? I do not wish to make it do such noises, I just want to understand why is it not making them.
  • Regarding the same valve, if I understood correctly the manual, if the side closest to the intake filter was disconnected when would hear a blow-off valve type of sound, because the blowback air would be dumped instead of re-injected into the intake. Is this correct?
  • Still regarding the same valve, If that valve was to be removed completely, would we start hearing that characteristic "stututu" sound?
  • On the manual they refer to "ramming", but I was unable to understand what that is. A Google search didn't help either.
  • Finally, does the connection to the manometer have to be after the throttle body, or could it be plugged between the inter-cooler and the throttle body?
2

I have noticed that this car does not make the loud whoosh sound we sometimes hear from turboed cars, is it because of the anti-stalling valve (tag 11 on the first diagram)? I do not wish to make it do such noises, I just want to understand why is it not making them.

I don't think so. The whoosh sound that you refer to is probably the sound of a "binary" waste gate "popping off." On your car the turbo is continually modulated by the solenoid valve (tag 6). This process is described on page 10 of the manual. It results in gradual changes in the level of the boost, rather than the sudden changes that would make the whooshing sound you're referring to.

The purpose of the anti-stall valve (tag 11) is to bleed off excess pressure that occurs in the intake when the throttle is suddenly closed. The pressure can cause a "compressor stall" by disrupting the air flow over the compressor blades as the resistance to incoming air suddenly increases when the throttle closes. This valve is also called a by-pass valve (BPV) when it returns air back to the intake.

Regarding the same valve, if I understood correctly the manual, if the side closest to the intake filter was disconnected when would hear a blow-off valve type of sound, because the blowback air would be dumped instead of re-injected into the intake. Is this correct?

Yes, but I think the blow-off valve sound is the sound you're referring to below, not the whoosh of the waste gate. With the return hose disconnected instead of recirculating the air, you'd be dumping it into the atmosphere effectively converting the by-pass valve into a blow-off valve and you'll get the sound you mention below. You would hear that sound at each shift, for example.

Still regarding the same valve, If that valve was to be removed completely, would we start hearing that characteristic "stututu" sound? On the manual they refer to "ramming," but I was unable to understand what that is. A Google search didn't help either.

What I think they mean by "ramming" is a temporary over-pressure condition in the intake immediately after closing the throttle. This is what causes the compressor to stall and what the valve seeks to prevent. If the valve were removed altogether, you'd experience "turbo lag" – stalled compressor won't be able to respond as quickly or as smoothly when you open the throttle again because it would first have to reestablish smooth airflow over the turbo blades again.

Finally, does the connection to the manometer have to be after the throttle body, or could it be plugged between the inter-cooler and the throttle body?

I would think you'd want to install it after the throttle body so that you could see the actual pressure in the intake manifold. That way the pressure drop across the throttle plate will be reflected in the gauge reading. If the gauge were plumbed in before the throttle, you'd see the available pressure rather than the actual pressure in the intake manifold.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.