Gm 10066036 block or 3970010

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RT Machine
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Gm 10066036 block or 3970010

Post by RT Machine » Wed Jun 13, 2018 8:03 am

I have a choice of 2 clean std bore blocks to use for a 383 mild street build max 500 HP, 1 is 3970010 4 bolt with good sonic test etc
Other one is GM Goodwrench Mexico build 10066036 4 bolt with little use, not yet sonic tested.
Is there any advantage in using the Mexican late model 2 piece seal block ? if so, can anyone let me know details ? as I have never used one for a performance build,
Thanks in advance.

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Re: Gm 10066036 block or 3970010

Post by Roundybout » Wed Jun 13, 2018 9:08 am

I'd sonic check them both, measure them up and used the best one. There's really no difference other than if they were cast and machined correctly and something OEM can vary in that respect of course.

I've seen mention of higher nickel content in the later blocks but I call BS unless someone can confirm. They moved production to save money. I doubt they are investing it in better metallurgy.

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Re: Gm 10066036 block or 3970010

Post by KnightEngines » Wed Jun 13, 2018 9:28 am

I've seen real bad lifter bore positioning in the mexico blocks.
I'd use the other one.

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Re: Gm 10066036 block or 3970010

Post by mag2555 » Wed Jun 13, 2018 12:10 pm

I would bet that you would get a chuckle if on the south of the border block you check the tilt of the Cam Bore in relation to the Crank Bore front to rear!

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Re: Gm 10066036 block or 3970010

Post by Olds455 » Wed Jun 13, 2018 1:44 pm

Roundybout wrote:
Wed Jun 13, 2018 9:08 am
I'd sonic check them both, measure them up and used the best one. There's really no difference other than if they were cast and machined correctly and something OEM can vary in that respect of course.

I've seen mention of higher nickel content in the later blocks but I call BS unless someone can confirm. They moved production to save money. I doubt they are investing it in better metallurgy.
I thought "high nickel" blocks were proved to be BS? And that 010 and 020 only identified the core box used or whatever the process is.

The numbers you are talking about (010, 020) are only sand core identification numbers. The 010 is a side core for a small block chevy, and it does not guarantee that the block is a 4 bolt or not. Most were 4 bolt blocks, but some 2 bolts were built with 010 side cores, or whatever side core was available. The 010 designation has nothing to do with metallurgy (nickel content)
I'd be more inclined to believe someone who works at the foundry over 5000 people that are just repeating what they've read and heard over the last 50 yrs.


And I thought Ford had the good Mexican blocks? And now people are automatically assuming any Mexican block from any engine and manufacturer is better? I'd think people here were more intelligent than that?

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Re: Gm 10066036 block or 3970010

Post by groberts101 » Wed Jun 13, 2018 2:14 pm

Olds455 wrote:
Wed Jun 13, 2018 1:44 pm
I thought "high nickel" blocks were proved to be BS? And that 010 and 020 only identified the core box used or whatever the process is.

The numbers you are talking about (010, 020) are only sand core identification numbers. The 010 is a side core for a small block chevy, and it does not guarantee that the block is a 4 bolt or not. Most were 4 bolt blocks, but some 2 bolts were built with 010 side cores, or whatever side core was available. The 010 designation has nothing to do with metallurgy (nickel content)
I'd be more inclined to believe someone who works at the foundry over 5000 people that are just repeating what they've read and heard over the last 50 yrs.


And I thought Ford had the good Mexican blocks? And now people are automatically assuming any Mexican block from any engine and manufacturer is better? I'd think people here were more intelligent than that?
It's a Ford myth as well. I've compared them side by side to others of similar era and only differences were in the main caps and webbing being heavier.

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Re: Gm 10066036 block or 3970010

Post by Roundybout » Wed Jun 13, 2018 4:09 pm

Its a crap shoot with production blocks. Having a couple or few to choose from, I wouldn't be worried as much as where it was cast. They've been having bad days since 1955 wherever they're casting them lol. The one that will clean up with the least amount of work/time would be my pick if I was using an OEM block.

Now I don't know if its true but I read some machinists say some blocks "cut" different when boring/honing. This applies to aftermarket blocks compared to OEM mostly but I've seen it persist between different year OEM blocks. Has anyone ever bored/honed a block and reject it because it "felt' different?

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Re: Gm 10066036 block or 3970010

Post by RT Machine » Wed Jun 13, 2018 7:53 pm

Thanks for replies, appreciate it :D

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