8 inch converter questions...

Years ago I broke my good 340 so I put in a 318 that a friend had ,put on a ld4B intake a mild cam and unported 360 heads with headers and mufflers it was going 13.20-30s with 3.91 gears. I had a 904 with a manual valve body and a 10 inch convertor. I put in a Turbo- Action 4600 stall 8 inch convertor and it started going 12.70s, I don`t remember the 60 ft times and it wasn`t driven on the street. When I fixed the 340 I put in a 557 lift M/P purple shaft cam, heavily ported J heads and a Victor 340 it went a best of 11.36 but with 4.56 gears. Same convertor and trans.