Originally Posted by 69firebird69
hello everyone I am new to this forum. I have an engine that was in my firebird when I bought it. Unfortunately its not numbers matching. I am trying to ID this engine. The engine date code is M156. I think the casting number is above it but I only see a partial number since there is a 3/8th set screw where the numbers begine. The partial number is 6133. I think the number infront of the six would have been an 8 but half of it is cut off looks like a 3. front of engine has a YD code. The heads are a 143 date code of M196. There are 3 freeze out plugs which I have read started in 67. There are no embosed numbers outside the engine or in the valley pan indicating a 400. I also read they didnt start that till 68'. I am looking for confirmation that this is a 1967 engine. I saw a link that said in 1966 YD was a 389 290 HP but in 1967 a YD was a 400 290hp. also I dont have any numbers by the timing chain cover. Any help would be appreciated.
Both date codes that you gave were for December of '66, so they were cast for 1967 model year. The YD engine in '67 was 290 HP 400 cu. in, 10.5:1 compression, 2 bbl with an automatic transmission used in big cars. The block casting number, found behind and below the passenger side head, should be 9786133.
By the way, welcome to hotrodders and you might go down to the lounge and tell us about yourself.