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Old 05-12-2005, 01:53 PM
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Bore size question

i bought a 72 Buick 455 a while ago and the seller told me it was rebuilt .30 over in his shop class. the stock bore size is 4.312, so by my calculations, the new bore size should be 4.342. well i took of the heads and measured the bore size and it was at 4.307 the walls look brand new, so i imagine he did some sort of machining work to it but it doesn't make sense to me.

i ask this also because i wanted to install new pistons and i don't know what size to get them.

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Old 05-12-2005, 02:02 PM
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Look at the pistons.......if they are .030 over, it is usually stamped on them.

Why are you wanting new pistons?
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Old 05-12-2005, 02:16 PM
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more compression=more HP, i figured out that if i have 10:1 comp, ill gave close to 400HP according to that nifty calculator i found here

but that still doesn't explain why i have 4.307?
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Old 05-12-2005, 02:36 PM
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The block is probably standard. If you are using a telescoping gauge your are likely to be off a little. Use an inside micrometer. If you ARE using an inside micrometer, it's out of adjustment.

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Old 05-12-2005, 02:53 PM
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Quote:
Originally Posted by 53LEDSLED
more compression=more HP, i figured out that if i have 10:1 comp, ill gave close to 400HP according to that nifty calculator i found here

but that still doesn't explain why i have 4.307?
First off, what did you do to obtain your current compression and horsepower figures?

Secondly that seems like a whole lot of work to gain 10-15 horsepower. Why not wait until the engine NEEDS a rebuild to do that sort of work? There are plenty of other things that can be done for less money to boost your horsepower the same amount. Ripping down an engine to gain another point of compression for a few more ponies just seems stupid to me unless its the ONLY thing you can (or is left) to do to make those last extra ponies of power.
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Old 05-12-2005, 06:55 PM
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Besides, if the machine work in it is good, it would be silly to change pistons, for several reasons:

A) They need to be balanced
B) When you send an engine to the shop, they bore each cylinder to give the proper clearance relative to the specific piston that's going in that hole. You'd be messing that up.
C) 10:1 is a lot of compression with iron heads.
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