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Original Message
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| What the heck you wanna overbore the thing for? |
| By Dave Shoe - 03/09/2001 7:46:38 PM; IP 12.2.11.131 |
If you wanna bore your block out to the last possible inch, your talking to the wrong dude. Overboring bores me.
Thin cylinders flex, blocks overheat, and engines just don't perform well. Fragile blocks are embarrasing, too, because they break when you push them.
Your goal of 425HP can be made reliably with a 352, no sweat.
A 425HP 428 sleeper would be cheap to build, dead smooth at idle, silent on the street and freeway, and only scream loudly when tromped on. You can make one loud, too, but with only 425HP it's NOT gonna sound all that menacing, especially if you make it loud using performance mufflers (the correct way to make a car loud is with the camshaft - a good cam will make Cadillac mufflers sound mean as hell, and make racing mufflers sound frightning).
I could look for a link to some posts that talk about different cylinder wall thicknesses in different FE engines, but you're way off the track and need a different kind of guidance.
You need to realize that cylinders don't just determine raw cubes, they also provide piston restraint at the "thrust faces" allowing the piston to travel in a straight line as it moves up and down the sleeve. You guessed it, thin walls flex and the piston no longer travels exactly straight. Very importantly too, the cylinder is used to communicate headbolt torque to the crankshaft (this is why most later 427 blocks have square cast "reinforced" cylinders, as these four corners to the cylinder reduce headbolt distortions and hold the whole block together better. Some 360-thru-428 blocks got thicker reinforced cylinders but 427 cylinders are so big they had to make them squarish to add any material). Flexible cylinders allow the whole block to flex more and the added strain promotes the collapse of cylinders.
Seriously, you can safely bore a non-sonic checked 428 +.000-over without sleeving. Yup - thats a "zero". Unless you know what the core shift is, you don't know how much you can safely overbore a block. Some stock bore 360/390/410/428 blocks will have walls as thin as .100" thick due to core shift and should not be bored if performance is a goal. They can only be "offset bored" after being "sonic mapped" if performance and reliability is desired.
Core shift is common with FEs, and the +.000-over situation is potentially present even in FE blocks sporting reinforced main webs, because many "reinforced main" blocks do not have thicker than-stock cylinders.
Any boring you do reduces the reliability and strength of your engine, and reduces the usable lifespan and resale value because it reduces the number of times you can bore it when it really needs it.
Shoe. |
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