I have purchased a 1966 396 block casting # 3855961 with pad stamped TO5301AR. What is the AR stand for? Also, at what web site can I gain access to these suffix codes? i am having trouble locating this info. Thanks !!!!!

Are you 100% sure of all these digits? TO5301AR

The 1 does not fit, could it be some other letter or number.

T - Tonawnada Engine Plant (NY)
05 - May
30 - Day
?AR - Engine suffix code

In 66 only,the third digit is the Carb
IA= Impala 396/325 L-35
R=Rochester carb

This Camaro site has suffix codes, there are some errors, but still one of the better lists
http://www.nastyz28.com/spmenu.html

Rene
66_Malibu

Thanks for the info. I double checked the stamping and it is IAR for the last 3 digits. I thought this block was for a 360hp Chevelle but the block must be from a 325hp Impala.

I thought this block was for a 360hp Chevelle but the block must be from a 325hp Impala. They ARE the same block, just the stamped numbers differ...