with running 555cc is that you bump up the duty cycle(on AVCr) real high to get the proper boost. There is some debate on this "it's not safe to run close to 90% duty cycle"(try search on duty cycle) but there is no final word that I can find. If you go with TD05 I would go 720cc just so your safe. With an AFC you will have no problems finding a safe boost/fuel curve. My .02