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Original Message
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| Victim of cheap boring. |
| By Dave Shoe - 01/11/2002 12:27:13 PM; IP 12.2.11.131 |
Since the bore center is about 4.63, and the bore is about 4.23, there is only .400 between cylinders on a new 427 block. With a 1/8" drill bit between the bores, there is only .275" of metal remaining, divided between two cylinders you've got .135" each wall.
Since core shift of .030" can be considered miraculously small in all eight cylinders, it's not tough for a stock bore 427 block to have a wall of .105" or more. Bore it .060" over and you've got .075". This is not a good number to be racing with.
Offset boring would have been one good solution, as it allows the thin wall to receive a minimal cut, while cutting more from the thicker wall. Not many shops do this, and if you bring the block to a regular shop, they're just gonna bore down the center.
A sonic map will let you know what course of action should have been taken in prior borings of the block. Mapping after the bore can be painful and expensive.
You should give us more numbers from the map. .065" is too small for me to play with without more info. You should let us know whether it's got round water jackets or cloverleafed jackets, and also what the various cylinder thickness numbers look like, in particular whether the weak numbers are on the major thrust, minor thrust, or non-thrust surfaces, and what the numbers look like on the opposite face of the cylinder from the thin spots.
Also, how do you intend to drive it. Weekend track brawls (what brackets), or daily driving (what brackets). Compression, cam, and RPM plans also fit into the formula. Invariably, .065" is scary, though.
Shoe. |
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This thread, so far...
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