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Old 07-06-2008, 10:45 AM
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Value of 400 small block? 3951509 2 bolt main



Hi guys hows it going?

So my wife and I have a 1978 chevy motorhome, it has 48k miles on the clock, but the motorhome is pretty hammered so it will be going away in the next year or so.

I checked out the casting number, its a 3951509 from 78' so its has 2 bolt main. I've never driven it hard, most always 55 MPH or slower, ~10 MPG driving it like that. Its never been overheated, runs like a champ.


I found this quote here,

Quote:
The 3951509 block is the most sought after 2 bolt 400 block. Some have the better metallurgy with 1% added tin and 2% added nickel, which increase the strength of the cast iron block A LOT. The added nickel is used in a lot of newer blocks, GM and ford among others. I have heard of guys taking 5.0 'stang engines apart at 100,000 miles and not even needing to bore them to rebuild with the cylinder bores checking out like new still, as the added nickel blocks wear so much better than the older cast alloy formula. 010 and 020 numbers will both be stamped usually under the timing cover area. Strange thing on mine, they are stamped on the side of the block, smaller, near the deck. Never seen that. These I believe are also the "cheater" blocks, as you can pass them off as 350's because they have the same amount of freeze plugs on the sides - 2. 8" balancers also are a giveaway that it's a 400, but you can buy externally balanced 6" harmonic dampners. Then the only clue that it is not a smaller sbc would be the casting numbers.
Estimates on what its worth? Where would be a good place to sell it? I noticed there are no classified here.

Thanks in Advance.

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Old 07-06-2008, 11:26 AM
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http://www.hotrodders.com/ads/

Yes there are classifieds.

The block and crank is all that would be of any real value. Even with that, you don't know for sure if the parts are a good candidate for a performance application- e.g. engines do run with cracked parts.
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Old 07-06-2008, 02:24 PM
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It has been a couple of years ago that I bought a low mileage motor home SB 400 two bolt for $150, complete. I tore it down to ship block only to an IMSA engine builder that machined for high dollar splayed 4 bolt caps and built to 680 HP. This block was his block of choice because of the higher nickel content. He believed the increased Ni aided in a more uniform and stronger casting that would withstand the constant pounding of the high horsepower/reving of racing motors he built. The low cylinder wear in the 5.0 referred to in the posted link is because of the EFI, not the content of the block casting. Most EFI motors would live quite well to 500,000 miles if the rest of the vehicles were built as well. EFI does not have all the excess unburned fuel washing the cylinder walls as the carbed motors of old.

Trees
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Old 07-06-2008, 02:51 PM
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Quote:
Originally Posted by trees
It has

The low cylinder wear in the 5.0 referred to in the posted link is because of the EFI, not the content of the block casting. Most EFI motors would live quite well to 500,000 miles if the rest of the vehicles were built as well. EFI does not have all the excess unburned fuel washing the cylinder walls as the carbed motors of old.

Trees
Not entirely correct.
10 years ago I was still personally boring and honing blocks and some of the later 5.0 blocks (one piece seal) were very hard. They squeeked when bored, almost as much as some of the diesel blocks. (no pun intended) Occasionally find a 5.7 Chevy too.

Harder alloy cast iron, different honing techniques, different ring widths/ tensions, and materials, as well as better oils, and fuel injection, all contribute to longevity.

I have a 90 5.0 lo-po with 276,000 miles on it that does not smoke, has good compression, and still gets 24+ hwy mileage @ 70 mph in a 4500# TownCar. Never had a valve cover off. Mobil 1 synthetic oil since 70,000 miles. Perfect transmission, Mob 1 ATF.

About 6 weeks ago I pulled heads off a 89 Vic lo-po with 135,000 miles with virtually .001 of bore wear. The engine /AOD is going into a rod.

Interesting note. This 90 has always been a little slow to start. Not bad, just 1 1/2 seconds, you know, spins 3 turns. Used to bug me 15 years ago. Dug around and found out that the computer is programmed that way to get a dab of oil pressure moving before lighting it off.

Oh ya, and the 400 SBC 2 bolt with splayed 4 bolt Moroso caps was the block of choice for main strength.
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Old 07-06-2008, 03:00 PM
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Hmm, I have a bare 400 "09 block sitting out back and couldn't even get 200 bucks in the local paper. Crank is already 20/20 so it's not that great. Rods are ok. I dunno, maybe someday i'll build it.
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Old 07-06-2008, 09:36 PM
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Quote:
Originally Posted by Jmark
Hmm, I have a bare 400 "09 block sitting out back and couldn't even get 200 bucks in the local paper. Crank is already 20/20 so it's not that great. Rods are ok. I dunno, maybe someday i'll build it.
If I could only get $100 or so for it it would hardly be worth pulling :-/

Thanks for the info guys
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Old 07-06-2008, 09:43 PM
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Well, when any of you decide that you no longer want a 400 in your way, PM me and maybe I can help. Good blocks are scarce these days in some places. There are many rodders and racers who would put that to good use. I'd add it to my collection, for use later. Hmmm...
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Old 07-06-2008, 10:13 PM
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I'll do my best to make sure it doesn't get wasted. It'll be a while before I get around to "dealing with this", but it would be nice to know our house engine will live on in a fast car
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