PTC 8" here. Great service. The last 3 converters I've owned were 8" behind 425hp - 680hp motors and no problems (2 were on 727's, the latest one is a 904). We had a 9" behind the 580ci low 9 second car, that also saw some street use. It worked well too. All from Dynamic, Midwest Converters (now defunct), and PTC.
