>From what I've read, the unleaded heads were being phased in for the '72 model year, along with the lower compression ratios. By '73 everything should have been unleaded. I believe cat converters were phased in during '74, and unleaded was mandatory for the cats to live. Rob McCall '67 LeBaron, lead-head (but I do have a pair of '452 casting heads on the shelf if necessary at a future date). ----- Original Message ----- From: clgilleland@xxxxxxxxxxxx To: mailing-list@xxxxxxxxxxxxxxxx Subject: IML: Unleaded or Leaded gas Date: Wed, 8 Mar 2006 00:36:57 -0600 Hi, I was wondering When did Chrysler start putting hardened valves in engines so they could br ran on unleaded? I have a 74 Imperial with a build date December of 1973. Fred Joslin ----------------- http://www.imperialclub.com ----------------- This message was sent to you by the Imperial Mailing List. Please reply to mailing-list@xxxxxxxxxxxxxxxx and your response will be shared with everyone. Private messages (and attachments) for the Administrators should be sent to webmaster@xxxxxxxxxxxxxxxx To UN-SUBSCRIBE, go to http://imperialclub.com/unsubscribe.htm