Auto Racing: vacuum pump, vacuum pump, airpressure

Question
I got one for you!..I am building a Kenworth pickup and it has a big diesel and an air compressor mounted(belt driven)..anyway this truck is gonna have vacuum and hydro boost brakes on it.Can I make the air compresser in to a vacuum pump while also using the air side to control air bags under the frame?This is bugging me..what would I have to do to make the compresser keep me a tank of vacuum while still being able to use airpressure for my air ride?..Your help would be appreciated! Rusty

Answer
Here's a question I don't get every day.  Seeing few diesels in racing (we should though if you remember Renault kicking everybody's backside with a diesel lemans engine turning 12 grand).
  The compressor would ultimately be reversed to act as a vacuum pump, and being not designed for it, wouldn't be very efficient.  You would also end up with a complex and expensive set of solenoids and valves to switch from one operation to reverse. It's an excellent idea though, but I think simplicity would make it worth mounting another pump and creating a pulley drive for it.