stock 400 chevy crank

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b73
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stock 400 chevy crank

Post by b73 »

Hi Guys,
My question is, how strong is a well prepped stock 400 crank, #3951529?
The engine in question won't see big revs (max 5800-6000), but will see big torque numbers (7-800 ftlb) as it is a turbo application. Will a good stock crank live, or should i go aftermarket? If it was going to be a sky-high revver, I'd replace it regardless, but I'm unsure of the stresses induced by a low rpm, but still reasonably high hp/tq application.
TIA.
bill jones
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Post by bill jones »

-I think it's a bad idea to even consider it.
-The externally balanced front damper has always been a problem on any 400's I've been involved with, and the weights on the flywheels have been known to break or come completely off if left welded like stock.
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-I've seen the snouts broken off, front rod throw of the crank broken thru the lightening hole to the front bearing radius, and the arm from the front throw to the 2nd main, and just about every other arm broken except for the wide front and rear arms.
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-Those cranks have been OK to about 450 HP and 450 pounds of torque on oval track engines but when you start getting much over that they just fall apart.
-I've even had the journals hardchromed which never hurt anything and I've polished and shotpeened those arms and the radius's that break and that helps a lot but those cranks are loseres in my opinion.
-Think about the cranks-they were born in the early 1970s', 30 years ago.
-I personally wouldn't use any externally balanced 400 crank on any engine that runs over 5500 and I wouldn't waste the money again to ever internally balance one.
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-Then the next problem is if you go to a decent crank you still probably intend to use a stock block.
-This is another loser when you get to and above 450 REAL hp and 450 REAL torque.
-The main webs break and the the rear main cap breaks, then the cylinder walls crack vertically at the 5 vertical notches inside the water jackets below the head bolt holes of each cylinder.
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-I don't like the idea at all, BUT---there's probably guys out there who do it every day.
Fkned
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Post by Fkned »

I think your better off w/ an aftermarket crank also.The 383 cranks are very nice even though they have 350 mains you can get spacer bearings to fix that.I don't know if balancing will be any problem w/the heavier pistons,anybody else know?
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Post by CNC BLOCKS »

I also don't have much faith is a stock 400 crank in your application and hopefuuly your stepping up to a better block with the torque that your going to be making.

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Post by jdperform »

I bought 30 400 blocks & cranks 10 years ago from a core supplier. And one by one the cranks failed magnaflux. I believe it's the external balance forces working against each other that causes it. The 377's seem to last a long time but they are internally balanced. The cut down 383's had trouble also.
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Wolfplace
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Post by Wolfplace »

Agree with all of the above except going to a 383 crank with spacers.
This is the wrong way to go with that kind of torque as it makes the crank inherently weaker due to less overlap.
This is I believe the main reason GM when to the larger mains in the first place.
Get a good forged crank, stay with the 400 mains & use a 6" rod so you can internally balance the engine without the expense of Tungsten,,,

My personal preference is to internal balance everything I can,, the closer you put the weight to where it is needed the happier the crank & bearings will be. :wink:
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