Like has been mentioned before, teens need compression, improved intake/exhaust, and camshaft. Basic hot rodding really. Even 340's that were purposely built as a performance engine can benefit. The 72 and 73 340's can benefit from the list of 3 improvements as well. Almost all of the 318's and 360's were designed with a 2 barrel and to be used as a basic powerplant and not a performance offering like the 340's were.