I was thinking about buying a choice 3951509 010 020 virgin block for $500, but then I decided to get some calipers and check out the two blocks that I have already, since they both have a minor amount of coreshift.

One has freeze plugs in it, so I could only get the bow calipers through the large deck coolant holes to guage it.

The 3951511 4 bolt is a fresh 4.155" (030) bore, and measures .232"-.255" (some front to rear coreshift).
The 330817 2 bolt has has a ridge at the top of cylinder #3, all other cylinders measure pretty good. Probably needs to go .020 or .030 over. This one, virgin bore, measures .252-.325" (has more coreshift, and side to side vs the other one ft to rr, but thicker walls). So after boring, the thinnest will be .222" or so.
This isn't taking into account one factor. Due to the 400 being such a large small block bore, where the head bolt holes are in the deck, you can feel inside the freeze plug holes where the cylinder walls were cut into where the holes for the head bolts were drilled. I assume they are all this way, as the bores vs head bolt location are not changeable in coreshift. These areas on the block w/o freeze plugs measured around .167" or so.

Since they are a siamese block, does that make the cylinders more rigid, since they are all connected???

On Camaros.net, a few people thought that the minumum bore you can safely run in a siamese block is around .135". Taking these thinner areas into account, I'll be just above that mark. I figured the minumum wall thickness would be a lot higher, thought maybe around .175" would be the limit, but then again, I've never really dealt with this before. I didn'd even know what coreshift was when I got these blocks.


Now... which block should I run? How much power can I run through these? I'll be topped out by around 5700rpm, with peak hp at 5100rpm. Probably 440hp+, and maybe 495 ft-lbs? Mostly street driving, some SCCA racing. No drag racing plans. I have heard the 330817 blocks are not as good supposedly (just opinions, no facts), more prone to coreshift. I saw one guy say he thought the alloy was a lot softer. The 4 bolt 3951511 blocks are a bad 4 bolt design (non-splayed outer bolts put stress in the wrong areas), and are known to crack more readily at high rpm use in the webbing between the cylinders. Not sure which block would be better to run... Instinct tells me the 330817, thicker walls, 2 bolt, but then again, that's a 77 block, the 3951511 is a 71 I think, so it's most likely a better alloy misture.

Not sure if I should get the 509... I figure 10 years from now I may be kicking myself, rather than having a killer block in my car and two extras on the shelf, when everyone else is stuck with 383's, big bucks for a 400 sbc original block or aftermarket block, etc... I also have two spare Super T-10's with nodular cases... Just a little precautious, I guess!

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'71 RS/SS project: fastburn rollercam 406sbc / 9.75:1 / 750 Competition AFB / big 4 whl discs, 1-7/16 VSE ft & 1" Rancho adj. rr sway bars / 4 speed 3.23 posi / 81 Z28 & dual snorkel vette Air Induction

I currently run a 511 block hard, no crack issues so far, a nice block.
Any concerns I would have for the 817 block would be from hearsay, I wouldn't concern myself about it (would use it)
From the sounds of it, the 509 is worth buying as that particular block is getting tougher to find all the time, probably a better investment than Enron.
You hit the nail on the head with the cylinders being weak where the headbolts are (scalloped in those areas) but a cheap easy fix here is a partial fill to the bottom of the side frost plug holes to help stiffen the bores. Having the bores siamesed just stiffens up the bores that much more, sonic test your average 350 block where the cylinders meet and don't be suprized to see as little as .090" wall thickness in an otherwise good looking core with no visible core shift.

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A Canadian, EH?

I have also spent a lot of time going over 400 blocks with calipers. I also use a small one thru the big water holes on the deck. I have a couple of .030" blocks that will easily machine to .060 and still have min of .175 or more all the way around on all cylinders. The core shift on one was more than it looked from outside but it still had lots of meat. From what I've seen and heard 150-175 is plenty especially with the concrete trick. ( I will use that one as well ) My sole concern MIGHT be uneven cylinder bore heat rejection from walls thicker on one side than the other.

I later got lucky and found a virgin 2 bolt 817. The decks havent been touched and the core shift is the least of the ones I measured. No fine hairline cracks at the capscrew to steam hole point like many have. Even tho I had 2 usable blocks I couldn't resist. I paid $200.00 Cdn and I got some cleaning in trade for the ( thrust burned out ) crank, short rods, and old heads. This is the one I'm using but I wouldn't be afraid to run either of the other two.

I'd be really torn. A Motown block is what? $1600 now. The integrity of the aftermarket casting is unparalleled by any GM casting. By the same token,,, $1100 will buy a LOT of parts.

$500 for a high alloy '509' casting probably isn't out of line these days. That's exactly why the aftermarket 400 blocks are selling like hotcakes.

<font face="Arial,Verdana" size="2">Originally posted by Chuck78:
The 330817, virgin bore, measures .252-.325" (has more coreshift, and side to side vs the other one ft to rr, but thicker walls). So after boring, the thinnest will be .222" or so.
</font>

Correction, .030" over would be .015" off of each side, so that would be .237" thick after boring.

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'71 RS/SS project: fastburn rollercam 406sbc / 9.96:1 / 750 Competition AFB / big 4 whl discs, 1-5/16 VSE ft & 1" Rancho adj. rr sway bars / 4 speed 3.23 posi / 81 Z28 & dual snorkel vette Air Induction

Dirt is running an 817 block into the 11's. Don't worry http://www.nastyz28.com/ubb/wink.gif

<font face="Arial,Verdana" size="2">Originally posted by camertom:
No fine hairline cracks at the capscrew to steam hole point like many have.</font>

Please forgive my ignorance, but can someone tell me exactly where to look for this? What is the capscrew?

Thanks,

ChevyReb

I have a Virgin high nickle 509 400 block with 2bolt mains and Im wanting to sell it with a new 7qt oil pan with pickup and Melling HV55 oil pump and a SFI approved 400 balancer for $400. Ill ship it if buyer pays for shipping costs. This is a great 400 block no core shift and it will go back to standard bore. Ill even throw in a set of ARP head bolts and the counter weight for a netural flywheel. Im gonna build a BBC now.

man, if I didn't have three already, I might just have to drive to Louisville this weekend! I forwarded this to a buddy in Cincy.

What a good deal! is it an 010 020?

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'71 RS/SS project: fastburn rollercam 406sbc / 9.96:1 / 750 Competition AFB / big 4 whl discs, 1-5/16 VSE ft & 1" Rancho adj. rr sway bars / 4 speed 3.23 posi / 81 Z28 & dual snorkel vette Air Induction

Yes it is.

Don't EVEN trust what you're measuring with your caliper. If you want a true test, have it sonic checked. I had 3 - 509 blocks and one 817. All of the 509's were pretty far out as far as core shift goes and the 817 was very nearly perfect. The cam bore of the 817 was farthest from centered and it had the least amount of cylinder core shift. If you look closely at the cylinder barrels thru a core hole, you'll see that the cylinders aren't uniform thickness like a 350 - they have alternating thick and thin areas that spiral around the cylinder like rifling on a gun barrel, supposedly to make them stronger. Have 'em magged first to eliminate even the small deck cracks that are so common in 400's, then if you have any that are perfect, have 'em sonic checked and pick your block

I remember when the 817 was the "black sheep" of 400 blocks. Now it seems they are some of the better ones.

I went to a swap meet in town today and I could not beleave what guys wanted for just a bare 400 block and most were junk ones at that. I think the cheapest one I could find was a 811 block and it was already bored .040 for $550 and they went all they way to $650 just for a bare block that was dirty as hell and rust in the cylinders. It crazy what people as at these swap meets. Im almost afraid to ask what the lowest ammout they would take for some things I looked at.

Yeah, I got the other two for pretty cheap, this virgin 509 I got recently has no coreshift and could be ran as is if needed I got for $400. Notice the guy on the board who posted his 509 010 020 casting from Alabama at $200 immediately thereafter took it off the swap meet section board most likely after he realized how good of a deal that was. Some may pay $600 for that block in that shape!

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'71 RS/SS project: fastburn rollercam 406sbc / 9.96:1 / 750 Competition AFB / big 4 whl discs, 1-5/16 VSE ft & 1" Rancho adj. rr sway bars / 4 speed 3.23 posi / 81 Z28 & dual snorkel vette Air Induction

ChevyReb,

A head bolt is a big "capscrew", the cap is the hex-head! Just another name to remember that bolts are called is all....

And it's for small heat-cracks between the head bolt holes and steam holes that need to be looked at closely on 400 block decks!

Hope this helps.

pdq67

<font face="Arial,Verdana" size="2">Originally posted by pdq67:
ChevyReb,

A head bolt is a big "capscrew", the cap is the hex-head! Just another name to remember that bolts are called is all....

And it's for small heat-cracks between the head bolt holes and steam holes that need to be looked at closely on 400 block decks!

Hope this helps.

pdq67</font>

Yes that is very helpful. I have not heard them called that before. I have two 400's for future builds. One is a matching numbers 71 511 two bolt that is still together. The other is an 817 2bolt bare block I will see if I can find any cracks in those areas.

Thanks PDQ67!

ChevyReb