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SBC Block

barhopper

Well-known member
I have the chance to get a motor from a guy at a very good price. The informatiom supplied by the seller is that it is a early 1980's motor.The problem I'm having is the guy claims it is a 400 cid but the casting number on the block is 3970010 (80-82) and after researching casting number it is shown as a 350 cid block. Can a 400 cid be built from a 350 cid block? is there any way to tell what motor it is without tearing it down.
 
A quick and easy way to spot a older 400
most older blocks have 3 freeze plugs on
each side Hope this helps. Jim
 
i looked up those numbers up and found that its either a 68 A body 327 or 69-79 car , truck , vette 350. the 400 numbers are3951511, 3951509, 3030817, 330817
 
Yes, I found the info on the casting but wondered if the 350 block could be reworked by cylinder boring and crankshaft change to a 400
 
Hey Hopper, The 400 blocks have a 4.125"std. bore and the 350 has a 4.00" std bore. The stroke on a stock 400 is 3.75" and 3.48" on a stock 350. On most 350 blocks you can not overbore the cylinders more than .060. So you can not get close to the needed 4.125" bore of the 400. The only way to get close to 400 inch motor is to stroke the 350 block to a 4.00" stroke and bore it to 4.060". I think that yields around 396" motor. Country has a 396 SBC so he can tell you how that combo acts on an airboat. When stroking a SBC that much you have to clearance the block in the pan rail area and at the bottom of the cylinders by the camshaft area. Also a small base circle cam should be used so the rods do not hit the cam. Also you will have to balance the rotating assembly because it will be all out of whack. I am currently building a 434" SBC so I have been thru this mess. Long story short,If you want a 400 buy one. It is cheaper and easier. I like the big bore block because the heads can acamodate larger valves and have less valve shrouding.If you want one built consult a professional engine builder like Waterthunder or Felber,they can save you a lot of headaches. And by the way, that motor you are looking at is a 350. Good Luck :)
 
010 is a 350 block. The best 400 block to get is the two bolt with the two freeze plug holes. To be honest 90% of car motor guy's would be happier with a 383! The 350 main web area is stronger, if you build a 383 be sure to use a four bolt block! Also the last 3 400 blocks I have bought were all cracked most of them crack in the lifter valley between the lifter bosses and the deck! A 383 is a great airboat motor for several reasons 1 the block is stronger, 2 the deck is stronger, 3 the smaller bore is less prone to detonation, 4 coolant can not flow around the bores of a 400 because they have Siamese bores!
 
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