Slow, the dart Jr's are a great head, but for my 347 I believe that they,re restrictive. If your going to a supercharger, they,ll be a definate bottleneck. I'll be upgrading to the AFR 205's with the nos port job fram afr. If the 205's seem to costly, Id consider the new roush 200's. The dart's are a great head, but I think a 347 would benefit from a larger head. my 2 cents
