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73-87 Chevy _ GMC Trucks => Performance => Topic started by: SNOWFREAK on November 05, 2002, 03:54:00 am

Title: CHEVY 400
Post by: SNOWFREAK on November 05, 2002, 03:54:00 am

WHERE DO I START? OK, I just found out last week that chevy made a 400 (call me a dummy) I bought a truck for $100.00 for the 12 bolt rear end, and got a bonus w/ a freshly built transmission and a 400 motor w/ 4wd  The motor threw a crank berring,  NOW the questions:
Is the 400 a rare motor?
Is it worth rebuilding?
How hard is it going to be to find parts?
I know it has the same bore size as the 396 and 402 BUT it is a small block so can it be bored more?
I don't have any specs in my manual for the 400, does it have the same pistons as the small block or big block? crank? heads? ANY INFORMATION ON THE 400 WILL BE A BIG, BIG HELP!!!!!

Title: PS
Post by: SNOWFREAK on November 05, 2002, 03:11:00 am

ALSO,  I am still confused on WHY they call a small block "big block based" if they made a 400 big block  

Title: 400
Post by: 73K20 on November 05, 2002, 07:36:00 am

The only help that i can give is to tell you that a 400 sbc is not an rare engine.  However, if your 400 should have a 4 bolt main then it would be a rare engine because the 400 with a 4 bolt main was only produced for about a year and a half.

1973 K20 - 350/350/205

Title: 400 small block
Post by: TMW on November 05, 2002, 07:15:00 pm

The 400 "small block" has a 4.125 bore (350 is 4.000)much as .060 over on a good block. But they are different in that all the external acc. bolt on but the crank stroke is a 3.750 instead of the 350 stroke that is 3.480. Also the main journals are smaller than a 350 crank and they are extrenally balanced and the 350 is internally balanced. And still another difference is the connecting rods are shorter 5.565 instead of 5.700 in a 350. The last main differences are the 400 has steam holes in between the cylinders  because they are closer together and and cannot use regular 350 heads without modifications. They came with 76cc heads and were relatively low compression,(about 8.0-1) but if built right are real torque monsters with just simple modifications. But if you want some real H.P. you can go a little deeper into it and build 400 to 425 horsepower realativly simply. Hope this helps TMW

Title: RE:
Post by: SNOWFREAK42 on November 06, 2002, 03:41:00 am

Where did you find this info on the 400? Manual would very helpful

Title: 400 info
Post by: TMW on November 06, 2002, 09:17:00 pm

Most any Chevy small block parts interchange book  will give the info and specs you will need.TMW

Title: 400 4-bolt?
Post by: 79SilveradoK30 on November 09, 2002, 03:20:00 pm

Does anyone know what years you could get a 400 4-bolt main block in a Chevy truck, and what models?

Title: 400 4-bolt main blocks
Post by: TMW on November 10, 2002, 07:50:00 pm

Be careful of them and have them checked out very carefully and magnafluxed by a reputable machine shop. Those were prone to cracking at the bottom of the cylinders nearest the outer main bolts because they were so close to each other. We have seen two out of three blocks cracked there. The two bolt main blocks are better and if your making some good H.P. a good machine shop can take a two bolt block and drill and machine it for splayed 4-bolt caps and you will be safe. Good luck TMW

Title: .
Post by: bored and stroked on November 14, 2002, 04:43:00 pm

Just to add a little bit. First, the mains on a 400 small block are larger then a 350's mains, not smaller. That why when using a 400's crank in a 350 block you must turn down the main journals.
Next, you dont really want a 4bolt 400. They crack in the main web area easy, and anything above 450hp is really not a good idea. 2 bolt blocks are a little better, and putting splayed 4 bolt caps on by a machine shop is the best idea [like TMW said]
Lastly, most blocks can only go .030" over. .060" over should only be tried after a sonic inspection, but chances are it wont go that far. Thats one of the reasons 400 blocks are getting so hard to find.

402 big blocks are completly different. You can tell real easy which one you have by looking at the exaust manifolds/headers. Small blocks have the middle two ports right next to each other in the middle with the two outer ports at the ends of the heads, big blocks have evenly spaced ports.

Title: Re: .
Post by: 77 K30 Crew Cab Dually on January 29, 2004, 01:29:00 pm

79silveradok30 had a question about where to find 4bolt main small block 400's. Those 4bolt main 400 were produced between 1970 and 1973. Your best bet would be to go and find any 70 to 73 caprice or impalla. You may also find them in that era of Chevy truck. The casting number should be 3951511. You should find that casting number on the top left of the engine right where the transmission bell housing bolts up. If you see the casting numbers 3951509, or 330817, you will know that you have a 2bolt main 400. If you see the casting number 3970010, 3970014, or 3970017, you will know that you have a 350. You must pay close attention to this to know that you have the right engine prior to pulling and paying for it. You will be mighty pissed off if you discover that you have brought the wrong engine home with you. Especially after all your efforts you put forth have been expended.

Check out your local book stores, or look at catalogs like PAW, Summit, Jegs and others. They will have many references to what you are seeking to learn  

Title: Re: .
Post by: roundedline on January 29, 2004, 03:15:00 pm

SBC 400's were offered in 73-87 trucks starting in 1975 and ending in 1980.  They were all 2bolt mains, but I am sure a few 4 bolts slipped in there from leftover surplus.  I agree on the 4 bolts, avoid them.

Chris Lucashttp://www.73-87chevytrucks.comhttp://www.captkaoscustoms.com