Adding boost will increase the stall of the converter ,but that won't help you now
You may have to try adding more brakes on the back to help hold it
My old pump gas Duster with the custom built 10 inch converter would push the locked up front 165x15 inch radials VW tires through the lights at 2300 RPM
I broke that converter and put in a T/A 8 inch race Hemi SS type converter and it went .2 ET quicker in the 1/8 mile and almost 2 MPH faster Way easier to drive at the track and on the street
Being in Brazil your facing a lot more problems in dealing with race parts made here in the U.S.A. than we do. Good converters are a great help in making the cars faster and better.
Bad converters are worthless, a total waste of money and your time on changing them, been there, done that
Don't buy a cheap converter or used "good race converter" unless you know it will work in your car like you want it to "