I want to add velocity stacks to my 1996 3sge engine basically cos they look cool. I have a few questions, firstly do i have to buy a quad throttle body set-up to get them? Can i run the on the stock ecu by just moving the air flow sensor? How much hp gains or throttle response gains can i expect from this setup?

I don't know if the 3SGE comes with MAP or not, but if you want to have velocity stacks you will need to purchase Individual Throttle Bodies (ITB's) and have you MAP sensor tapped into each throttle body. I don't know what kind of numbers you would be looking at, but to give a sort of number figure - a member on here Dyno'ed their 4A-GE silvertop at 115whp. I dyno'ed my silvertop with velocity stacks and had 130whp. Of course, dyno conditions were not the same, so I can't say this is a true representation. And I cannot say for throttle response.