Talked to Harold at Spitfire(Headers)

they definatley flow better then a 340 manifold thats for sure. when djvcuda put them on his car the difference over the 340 manifolfds that came off it was incredible. looking at them at first i didn't think they would work so well. boy was i wrong.. his car has been 12.50's with them..... i'm sure a tti or dougs header would flow even better but for the price ya can't really go wrong ..