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Finally got around to trying the manual boost in my auto '98 9-3 base. Of course, I couldn't wait for a controller to arrive by mail.
Instead, I built my own from parts I could get in town. Cost about $30. It is a bit different from the standard ball and spring -- I don't know if this is a good or bad thing. The unit is based on an article in AutoSpeed, linked below. Anyway, it is a two stage system composed of a pressure relief valve and a pressure regulator. The relief valve blocks pressure to the wastegate until it reaches a set value, and the regulator keeps the output at or below a set point. This not only allows you to specify the max boost pressure, but also the point at which the wastegate is allowed to creep. The article gives a much more detailed explanation.
Despite the fact that I couldn't get the softer spring needed to make the regulator precise at lower pressures until tomorrow, I decided to try the unit anyway. I didn't bother dialing it in completely, but did experiment with the settings enough to understand them. The imprecision of the regulator made it impossible to get the tuning just right. I did, however, get it to just below fuel cut.
This is the big disappointment -- apparently the AT T5 has a lower fuel cut than the 5 speed. I could get it about two needle widths into the red before fuel cut; not much more than stock boost. Oh well, I wasn't planning on permanently running it much past the stock level anyway -- I don't have the sport exhaust and also fear for the long-term survival of the transmission. Still, I would have liked to try it once or twice. My primary goal here is to improve the spool-up, and it looks like I can do that just fine. I wouldn't say the car is transformed, but it does seem faster.
I will give another report once I get the spring in and really tune the boost. Will have to see if the one-way bleed or more precise regulator detailed in the Audi Part II article is necessary, I'm not sure yet. I do really like the flexibility of this boost controller, however, and would like to hear about someone trying it on a 5 speed. I may also have to build a Grainger (Dawes) valve to compare results.
The only downside of the controller I've found is that it is really big compared to ball and spring valves.
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