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With the action of a ball-spring MBC the setting of the base boost is quite immaterial. The MBC will conrol when things open. And as it opens the WG at the latest moment, there are often boost pressure overshoots. These cause fuel cuts and the problem gets worse in cold weather when the rate of boost rise is much higher. The MBC simply cannot get the WG to open fast enough. How can you make the WG open faster?
I propose something else, that is counter intuative, that I have posted about years ago. You might be better off with a much softer WG setting, less than stock, so that once you are on boost and the MBC is flowing, that the MBC can get the WG open, faster, before you get a fuel cut. Obviously there will be a setting that is too soft, but I expect a 'stock' base boost setting is really too high. I also speculated that a MBC would work better if a pressure regulator were used to apply a base pressure to the WGA to apply some pressure in advance of the MBC starting to flow. Call this an anticipator if you like. That will be easy to adjust compared to WG adjustments.
I tackled this from the other direction. I installed a pneumo adjustable pop-off valve to blow off pressure overshoots. That worked quite well. The MBC was pressurized from the TB, so there was no boost droop as in a typical MBC install. That MBC config is the worst from an overshoot point of view, so the pop-off valve was a good combo for it.
Getting 14 or 15 PSI, with a good IC and a cold air intake can provide a lot of power! It is by no means slow. The stock turbo was way too small. A larger turbo will be more efficient at power and this will lead to a denser air charge and more power. A resistor mod on the MAP can get you another 1 or 2 PSI as well.
The stock boost control system creates a lot of controller boost lag. I think that Saab spec'd in a small turbo to compensate for that. That helps get thing going but the turbo can't deliver power properly!
With a MBC or SMBC most of the controller induced lag is gone and a larger turbo makes a lot of sence. With the action of the ball-spring MBC the larger turbo is not going to exibit a lot of boost delay. Note the difference between boost delay and turbo lag. They are not the same. With a MBC you are experiencing turbo lag and that is nothing compared to stock boost delay.
95SET 150K (rip)
posted by 207.43.195...
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