Your 361 came with 9:1 compression. The 400 heads will drop it to 8:1. Maybe less, since the actual compression was usually less than Chrysler advertised. If you use a modern, blue head gasket, that will drop it a teeny amount as well. So I'd say about 7.9:1, at best. I'd want mine a little higher, even on a street car. However, the better ports and larger exhaust valve will make up some of that lost power. I think I'd give the heads a substantial milling to try and bring that compression up. Don't forget, you will need the intake surface milled to compensate for heavy milling, but a competent machinist will surely know what to do. ---- Please address private mail -- mail of interest to only one person -- directly to that person. I.e., send parts/car transactions and negotiations as well as other personal messages only to the intended recipient, not to the Clubhouse public address. This practice will protect your privacy, reduce the total volume of mail and fine tune the content signal to Mopar topic. Thanks! '62 to '65 Mopar Clubhouse Discussion Guidelines: http://www.1962to1965mopar.ornocar.org/mletiq.html.