Quote:
Originally Posted by 1795
The engine builder wants to go .030 over as the block comes requiring final honing and going over gives him more room to adjust for discrepancies in the block bore that may be there. Since the pistons will be custom, they cannot be returned and if a cylinder requires over boring then, we would have to buy another set. Since we are getting custom pistons, he suggested that we order 10 instead of 8 just in case something happens to a piston, we will have a spare as it is not easy to get someone to build just one piston and it gets really expensive to have a small number built.
Not going to reuse the old pistons as we are dropping the compression ratio and they are popups. Also, pistons show some evidence of going lean at times with some heat spots that did not burn through. I am adjusting the fuel pressure and jetting and when it is all done we will be finalizing the air/fuel ratio on a chassis dyno so that we get more accurate information pertaining to actual use on the track as opposed to an engine dyno.
Jim
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I think that's pretty typical for older shops. A couple decades ago, piston diameters varied by so much that you had to sometimes custom tailor each cylinder to the piston. These days, pistons don't vary by more than a couple tenths (.0001") and there's no need for that.
Per MAStuart's point, it is a little beneficial to have the meat there for future rebuilds. The Dart blocks come in .005" undersize, which is exactly the amount needed to hone. Even if something were to happen (and things do happen), custom pistons can be made in .001" increments. If a piston had to be made for a 4.001" bore size, it could be done. Also, with most custom piston manufacturers, they give you a job number and getting a single is really easy these days.
If you haven't ordered pistons yet, you may discuss this with your builder.