Which year 400 engine?? - Pontiac GTO Forum
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post #1 of 6 (permalink) Old 10-06-2018, 07:25 AM Thread Starter
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Which year 400 engine??

Hi everyone. Another bright idea of mine. Over late fall and winter months, I might be looking around for a 400 engine to make into a stroker motor. I think a "461"?? I'm not going to stroke the original 400 motor in my '71. So, are there particular year 400's that are better suited to do this with?? Maybe stronger blocks?? Some years to avoid?? I just would like to start with a good block first and then move onto the heads as this progresses. I would like to be well informed in case I do come across something. Thank you.
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post #2 of 6 (permalink) Old 10-06-2018, 12:09 PM
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The best ones are from the late 60's early 70's. The only one I know of for sure to avoid is the one in the 70's with casting number 500557. It doesn't have as much material in the main webs and is not suitable for a high performance stroker build.


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post #3 of 6 (permalink) Old 10-06-2018, 12:18 PM
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I would go with a late sixties-early seventies block. I believe in 1975 the 400 casting was changed and there was less metal between the cylinder heads thus a weaker block. you may want to look at changing the heads on your seventy-one engine to increase compression.
I just stroked a 1968 ys block 4.25 stroke, 0.040 over on the bore, dished pistons to lower compression to about 9.5 (pump gas) and .068 Pontiac cam. It will be able to get out of its own way and then some.

If you want to go high compression, aluminium heads can dissipate the heat faster than a set of iron heads thus reducing the chances of detonation. The fact this engine is not an original engine you can have some real fun with it and not be constrained by the stock appearance. take a look at Butler performance to get an Idea of different rotating assemblies that are available. t
There are charts that will let you know how many cubes you will have at the end of build. Look around for a good block, 400 are not that expensive a 455block could set you back 1K or more. Have fun with this. Dean
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post #4 of 6 (permalink) Old 10-06-2018, 02:23 PM
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Doing the same thing with a customer's 77 TA. He's got the low compression 2 bolt main 400. He found an early 70's 400 block with the 4 bolt main and the better webbing. We'll be using that block with a butler 461 stroker kit. We also had to purchase the 4 bolt main caps from butler as the main caps that came with the block were 2 bolt mains even though it was a 4 bolt block.

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post #5 of 6 (permalink) Old 10-06-2018, 04:39 PM
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As mentioned, the 500557 block is one to avoid. Another is the 568557.

Also, some of the XX 481988 blocks used in '78 & '79, do not have the holes drilled for the 2-bolt motor mounts.

Some prefer the common '71-early '75 481988 blocks. The '70-up blocks, which have all 5 motor mount bolt holes, have advantages. They can be used in cars that use either 2-bolt or 3-bolt motor mounts. This is a good selling point, for anyone who may consider selling their engine, at some point in the future.

If you're not gonna add 4-bolt main caps, I've read that it's best to use a block that was not drilled for 4-bolt caps. But, some say that if you do decide to use the 2-bolt caps, it's best to install some allen head studs in the open holes. I have no idea if this actually helps strengthen the webs or not. ???

2-bolt caps with ARP main studs are said to be plenty strong for up to 600hp builds. So, some probably pay extra money to run 4-bolt caps they don't really need.
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post #6 of 6 (permalink) Old 10-10-2018, 01:25 PM
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What these guys said. The best ones are the early ones, pre-1974. I have heard but not validated that the '67-'69 blocks have the most nickel content in them and are the strongest of all. No worries stroking your present '71 block....you won't de-value anything or hurt anything, if you mothball the original crank and internals not used in the build.
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