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post #5 of (permalink) Old 08-24-2005, 08:00 AM
Junk Yard Genius
Join Date: Sep 1999
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Re: best boring size

Listen to the boys!
They are telling you true...

There are better ways of making (or freeing up) power than by weakening your cylinder walls!

First of all, YOU don't 'BORE' the cylinders, the block manufacturer does that.
You 'Over bore' cylinders.
'Standard' overbore (overbore sizes that most manufacturers make off the shelf parts for) are the way to go.
Custom made or fitted parts are a PITA.

Have someone clean and check your block for cracks, and have someone competent with a bore gauge check your cylinders for current size, and have them determine what the MINIMUM overbore you can get away with.
This is no time for an amateur to try and beat the learning curve, so leave it to the professionals.
You will have...
1. A 'Funnel' shape. The rings wear more at the top (farther away from oil, and the soft iron cylinder material wears more where it's hottest.) of the cylinder. Most of us are familiar with the 'Ring Ridge' at the top of a cylinder.
2. An 'Egg', 'Triangle' or 'Clover Leaf' shape. The cheap factory piston was ground cold to be round, but does not expand round when it gets hot. Connecting rod bosses have more material and expand larger than the rest of the piston body.
3. Cylinder 'Slotting'. With crankshaft rotation, the piston is forced up the 'Bottom' side of the cylinder (not under excessive force) and during the 'Power Stroke' the piston is forced down the 'Bottom' side of the cylinder under tremendous force causing more wear in that track.

If your cylinders only need 0.010" overbore to clean all of this up, then by all means, leave the extra material in the block (cylinder walls) where it can do some good!
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