Your typical street 347 will need an 1 3/4", a 1 5/8" WILL be a botlleneck! Depending how wild you go, you'll need bigger, but typically most 400hp set ups will use an 1 3/4". What combo were you wet dreaming over?
Grn92LX, I'm actually considering staying with my Systemax heads and intake and replacing my TFS Stage 1 with an FTI custom. Back when I knew considerably less than I know now, I bought the Systemax "Race" kit from the infamous Excessive Motorsports (Missouri). The heads and intake are "fully ported and flowed", so I might give them a chance to prove that I wasn't totally ripped off! Unfortunately, the intake valves are only 1.90's. Anyways, if can swing it I would prefer to use AFR 185's.