1985-1998 [Subscribe to Daily Digest] |
 | [Main 9000 Bulletin Board | BBFAQ |
Prev by Date | Next by Date | Post Followup ]
Member Login / Signup - Members see fewer ads. - Latest Member Gallery Photos
Wastegate actuator Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 1 Aug 2007 05:28:52
In Reply to: Saab 9000 Aero-Boost Capsule or APC Capsule, Tony, Wed, 1 Aug 2007 03:15:00 Members do not see ads below this line. - Help Keep This Site Online - Signup |
That part is more commonly known as the wastegate actuator. It is nothing more than a piston with a spring. As the boost pressure into the piston increases, it pushes against the spring. As it moves, it opens the wastegate on the turbo, reducing the boost.
The device on the radiator is the Boost Performance Control, or BPC. It has no sensing capability - it is just a valve. In earlier years, it was a solenoid - either off or on. In the newer cars (like yours) it is an valve controlled by the engine control.
The valve has three hoses. One goes to the intake manifold, one to the input side of the turbo (airstream), and one to the wastegate actuator. For base boost, all of the pressure is ported from the intake to the actuator. To increase boost levels, the valve opens some and bypasses some of the pressure back to the intake of the turbo. That means that it will require more pressure in the intake manifold to get the wastegate actuator to move.
Yes, you can mess about with the spring on the actuator, or the arm length. But is has less effect on a Trionic equipped car, as I assume yours is (are you in the US?) than in older cars. If the spring were stiffer, it would require more pressure to open the wastegate, so you'd theoretically get more boost. Or if the arm were shorter, the actuator would have to move more to reduce boost.
But that's not the way it works on the newer cars, like yours. The Trionic system measures the intake pressure via the MAP sensor mounted on the engine firewall. Say you made the spring stiffer to get more boost. For a given BPC valve position, the actuator wouldn't move as much. If the Trionic system thinks the boost level is too high for the conditions, it will just close the BPC valve a bit more, port more pressure to the actuator, and you'll get the same boost as before. No free lunch.
The system is designed to provide full boost unless there is a reason to reduce it, such as knock detected. So if your fuel economy is getting poor and the low end seems weak, don't blame lack of turbo.
When was the last time the engine was tuned up? New fuel and air filters? The exact right NGK spark plugs, gapped per the manual. Any vacuum leaks? What octane fuel are you using? If the engine is starting to knock, the Trionic system first cuts back on ignition timing, then richens the mixture some, and finally cuts back on boost. Under highway cruising conditions, you really aren't using very much boost at all, so if the engine is knocking, the Trionic will be adjusting ignition and fuel. Both ignition retard and fuel enrichment will adversely impact fuel economy.
The BPC and wastegate actuator really impact near full throttle actions - full boost level, how fast you reach full boost, taper off function. At part throttle (less than half throttle) crusing around, they don't really come into play.
posted by 192.249....
, Wed, 1 Aug 2007 05:28:52 <-- Viewing This Message
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
