Chrysler did not start stamping the engine plant into the engine number until the late 1960's. And when they started doing that, the engine plant was the first digit (preceded by a P), followed by the engine size, the 4-digit date of assemby (based on Chrysler's 10,000 day calendar) and the 4-digit serial number. There was no digit for the model year in the engine number - that was supplied by the partial VIN on the engine block >From 1960 until the above system was adopted, the first digit was the engineering department series letter (model year), followed by engine size, month of assembly, day of assembly, and shift number (if not 1st shift). Codes for "HP", "MP", "R", "P", "LC", "HC" were stamped after the block size while "T" was before. HP - High Performance MP - Maximum Performance R - Regular fuel P - Premium fuel LC - Low Compression HC - High Compression T - Truck engine H - Hemi (426-cid) Any variations from the norm for the engine's valve guides, bore size, undersize camshaft, undersize crankshaft , undersize main and rod bearings, etc. were stamped after the date of assembly. The "HP" and "MP" designations were used when an engine had different internal parts from the normal engines, such as camshaft, pistons, etc.. Otherwise, how would a mechanic know the engine had a special camshaft, for example? Chrysler's parts catalogues note when a part is for an engine other than normal. Differences in carburation are easy as the carburetor has a number attached to it. If anyone wants to shoot someone for the engine decode, blast away. I am the one who decoded his data tag ("99" engine code) and the engine number. Bill Vancouver, BC ----- Original Message ----- From: David Whitney To: mailing-list@xxxxxxxxxxxxxxxx Sent: Tuesday, September 13, 2005 10:20 AM Subject: Call me skeptical (was Re: IML: '65 Crown Coupe Ordered New w/300L 413!!!) "M" on the stamped pad is not a failsafe indicator of an "MP" engine. It could very well mean the assembly occurred at the Mound Road plant. The seller does not provide a photo or rubbing of the stamp. I have not seen a 413MP engine from '65. There was a 413MP in '62, which was superseded by the 426MP that was available in '65. The 300L's engine did have a different cam, but was not distinguished with the factory designation as high performance. Taking into consideration the methodology for measuring and reporting horsepower in the mid-'60s, I suspect the Imperial's hp was underreported to begin with. And then there's the fact that horsepower is not evident off the line. That is where torque and gearing show themselves. The 300L being Chrysler's sporty offering in 1965, it had a 3.23 differential and received a cam that gave it rubber-burning characteristics. Horsepower shows itself at high RPMs, where almost no Imperial spends its time. Since the seller is offering up this piece of information with the intent that the value of the car is greater because it has what "appears to be" a special engine, I would look for more confirmation. Coupled with the fact that the seller's ID is new to eBay, I say caveat emptor. Happy motoring, David Happy motoring, David '91 K-Imperial driver '66 Crown Coupe project '66 LeBaron dual air and every option known to man ----------------- 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