I looked at this issue for my 4.9 v8. I believe the dual core civic radiators supply the needed cooling (Series or parallel.... doesn't make any appreciable difference) with about 25% extra capacity (if I remember the numbers correctly). The triple core gives a little extra above that. When you look at the high output from performance modified civics, I think the performance triple core civic radiators are the way to go. Originally I had planned to use Jetta radiators, but they ended up being about 6" longer than I wanted forcing them to be angled too much to fit properly.