Why do low performance engines use a large convertor 11"-12" and high performance engines use a 8"-10" convertor? This seems backwards to me but every time I try and use a small convertor behind my Buick V-6 motor the 60' times improve but slippage kills every other number all the way down the track. I guess what I'm really asking is can you buy (order) a small convertor to work behind a lower horsepower motor such as a V-6 Buick that won't have so much slippage down track and I'm not talking about a lockup convertor? I asked my transmission friend and he just looked at me and said, get a bigger motor.