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So I have a 99 bpa ultra. I wanted to go with a smaller pulley to get a little more boost. I read somewhere that I can go with a 3.5" pulley without upgrading the fuel system or ECU. I was wondering about brands or pulleys that are the "go to". Also I would like to add a A Pillar boost gauge. Is there a replacement that works for these cars, and where is the best spot to attach the hose for the gauge. I still very new to these cars and appreciate any help in advance..
 

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Going to a 3.5" is just enough of a bump up to require a few other items for support. Typically intake, downpipe/exhaust, colder range plugs (AutoLite 104's gapped ~0.055-60", changed every 5-10k), and still may need some tune tweaks to run clean enough to not worry. This also assumes the vehicle is running tip-top before you start pushing it a bit more. Scanning live data with an OBD2 scanner like the $15 ELM Bluetooth one, or something more elaborate, will let you see the sensor data before and after changes.

Brand doesn't matter much, as long as they're made specific for M90's by the 4-5 vendors we have, and you use the specific pulley puller for superchargers (3-jaw here can most definitely ruin the M90).

The vac line you'll want to Tee a gauge from is running around the base of the M90 from the bypass valve solenoid, to fuel pressure regulator, to lower intake port, to MAP sensor on the rear.
 
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