Help Decoding a Crate 350


New Member
Jul 27, 2012
1965 Pontiac Tempest
Hello, I am new here and would like some help. I purchased a 1965 Pontiac Tempest with a chevy crate 350 and a crate th350 transmission. I would like to do up grades to the engine but want to know a base line starting point with the motor i have in the car; it has very few miles on it. I found on the block in front of the passenger side head the following;1M1124 then under that 5H04.
On the driver side rear behind the head on the block I found;10066036 and then " something" Mexico. The person I got the car from thought the motor was a 290HP. The car has a 12 bolt posi with 391 gears and this motor will not turn the tires; so i do not believe it has 290HP. Any help would be appreciated, If I know what i am starting with it will help me pick the right parts as my budget is tight right now. Thanks. :)


Staff member
Oct 7, 2012
1976 Chevy Cheyenne 1500 P/U
So, here's the short story on your engine, by the casting number, 10066036;
"10066036 - 1986-up 350 Car & Truck 2 & 4-bolt Passenger stick 1-piece seal"
This engine block was probably cast in Mexico, that became popular in the early, mid-'80's as a cost cutter for the big three.

It would take a deeper probe to find out the original exact horse power and such, but before all that digging, I'd check the head, intake and exhaust casting numbers to be sure they are are all 'like' components.
This engine probably came out of another vehicle, rather than a crate, and could at some time in it's prior life had the heads and other stuff swapped around.

But, as another member has posted, it's probably a 250 hp (when new) engine.
Good luck with your project!

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