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Old 04-06-2010, 10:22 PM
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427 tall deck

Hi I have a 427 tall deck I heard that if u put a 4.250 stroke crank in it and bore it a hundred over it makes it around a 520. Is this true and can it be done

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Old 04-06-2010, 10:38 PM
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nope this will give you 505ci, and only a machinest can really tell you wether you can go .100" over or not. but i have heard of it being done with those blocks. most anyone would tell you though that you should only bore the cylinders as little as needed to clean them up for rebuild, if you can get away with .030" then that is what i would do and it would give you a 489ci, .060 would give you a 496. but in order to put the 4.250 crank in it you will need to have it stroker clearanced
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Old 04-06-2010, 11:28 PM
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All the 520 c.i. kits I've seen for the tall deck blocks require sleeves.
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Old 04-07-2010, 10:30 AM
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So if I use a stock 427 crank and go .60 over that makes it a 496 or do I use a 454 crack. See iam building a truck pulling moter so a just trying to figure out the best match
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Old 04-07-2010, 10:48 AM
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OK, here we go with the "stack" tutorial......

Any block has a nominal block deck height. This is the measurement from the centerline of the main bearing bore to the flat deck of the block where the heads bolt on. A tall deck Chevy has a block deck height of 10.200", so we have to construct a "stack" of parts that will fit into this space, while hopefully putting the piston crown close to the deck with the piston at top dead center.

The radius of the stroke of a 4.250" stroke crank is 2.125" (half the stroke), so we will start there. There are BBC rods available in lengths of 6.135" (stock), 6.335" (0.200" long), 6.535" (0.400" long) and many other lengths so that a fellow can build pretty much any stack he wants to.

If a fellow wanted to build, for instance, a 505 with 118/120cc open chamber heads for a 13.0:1 static compression ratio to run on race gas or alcohol, he might choose a forged piston like this SRP unit with a 1.520" compression height.
http://www.jepistons.com/Products/139544.aspx
Now, if we had a 1.520" piston compression height and a stroke radius of 2.125", we could add those together, then deduct the result from the known block deck height of 10.200" and find out what rod length we would need to use to get there. Let's see...
1.520 plus 2.125 equals 3.645. If we deduct 3.645 from 10.200, we find we have to fill up 6.555" of space inside the block. Since the closest rod length to this will be 6.535", we will use that length rod and have the piston dwell 0.020" down in the bore at TDC. A fellow could cut the block decks any amount up to 0.020" to square them up.

If you don't follow what I'm saying here, PLEASE....ask questions....

Last edited by techinspector1; 04-07-2010 at 11:05 AM.
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Old 04-07-2010, 10:56 AM
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Quote:
Originally Posted by 84 chevy
So if I use a stock 427 crank and go .60 over that makes it a 496 or do I use a 454 crack. See iam building a truck pulling moter so a just trying to figure out the best match
Nope a 427 crank (3.76" stroke) with a .060 overbore is a 427 with a 4.31 bore

A 454 "crack" (4.00" stroke) will net you a 454 with a 4.31 bore

A 496 will need a 4.25" stroke
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Old 04-07-2010, 05:38 PM
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So what does a 454 bored 06 over get you. What would be better for truck pullen a 427 tall deck your a 454 cuz I have both ?
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Old 04-08-2010, 07:39 AM
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a 454 bored over .060" will make a 468ci. i still say that you dont want to bore a motor over moe than what it needs to be, so if it only needs to be bored 030" then just do that the extra 7 cubes wont net enough to matter.

either motor would do just fine, but i'm pretty sure you would have to clearance the 427 tall deck for a 4.00" crank so as far as machine work cost the 454 would be less and you always go with the motor with the most displacement. the 427 tall deck would be a good motor to make a large stroker out of.
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Old 04-09-2010, 12:12 AM
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Ok now that I no what crank to use what about the rods should I use the stock 427 rods or buy something else.
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Old 04-09-2010, 04:00 AM
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i think you can fit the 4.250 crank in without any clearancing, i might be wrong here but im pretty sure i read that somewhere, someone please correct me if im wrong.
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Old 04-09-2010, 10:41 AM
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Quote:
Originally Posted by 84 chevy
Ok now that I no what crank to use what about the rods should I use the stock 427 rods or buy something else.

we need to know what crank you plan on using first
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Old 04-09-2010, 11:23 AM
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Iam going to use a 4.250 stroke crank
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Old 04-09-2010, 12:48 PM
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4.25 crank
6.8" rod
1.27 pin height piston

thats a 10.195 stack, which would be just about perfect.
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Old 04-09-2010, 12:52 PM
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then your best bet would be to buy a stoker kit with a 4.250 crank, 6.535 rods, and a piston with a 1.520 compression height like Tech1 mentioned in an ealier post, this will give you a stack of 10.180 and since the deck height is 10.200 then you will have a .020 clearance between the piston @ TDC and the deck height, this will also allow you to plane the deck if needed in order to get a level surface for the boring
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Old 04-09-2010, 12:59 PM
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Quote:
Originally Posted by b00tz
4.25 crank
6.8" rod
1.27 pin height piston

thats a 10.195 stack, which would be just about perfect.

this will work too, but doesn't really leave you any room to deck the block
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