manually locking the converter in 3rd
 

I am thinking of making my converter lock up in 3rd I have a 3,200 midwest stall. I was talking to a guy I know who has on on his car. He said I just have to ground one wire with a toggle switch. which one? and would I see any gain in the 8th from this? I trap at 96mph in the 8th. with a 3.23 gear and a 121 in the 1/4

Plus the pro's and cons of this.
Thanks Sean