Re: Engine question!!
Although I've been around cars for quite a few years and stripped and built a few engines myself. On a V like ours, the bores tend to wear most on the thrust side of the block, thus without mounting the block in a boring machine or other machine tool or fixture, it isn't easy to determine how the block has worn and what 0.017" of bore wear actually means. That is just a measurement, but dosen't tell you how it relates to the concentricity of the original bore.
It could be that the ovality of the bore is only 0.010", with the other 0.007" of wear on the non thrust side (doubtful), this might just clean up with a 0.030" overbore. That said, you need a couple or three thou for the final finish honing, so it could be close.
Like has been mentioned, setting up the block and machining it costs the $$ to the machine shop and they will want the pistons to measure before they machine the bores to fit them. If the shop you are using are amicable, they should be able to actually clock up (measure up) and determine what the 17 thou means, or, at your request see if they will clean up at +30 thou over.
At the end of the day, time to them is money - how much do you want to spend? Like has been said, do you want to pay twice? They may also not want that hassle, unless they share your enthusiasm. They know that a +0.040" overbore will be easy to achieve.
Good advice already given on piston options for the popular + 30/40 option.
My philosophy for strength is to remove the least amount of material as possible, to deck the head less and use a thinner gasket to achieve optimum piston to head clearance.
If thin cylinder walls really are a problem on these engines at the level you are going to be at, would you be better off looking for another less worn block to start with? Is your block a bad one? Certainly for the sbc, there are blocks that have higher nickel content in them than others???
On a different but still block related theme, but making an assumption that you will be square decking the block. I will first be honest and say that I have never stripped a turbo six, sbc's yes and the general concensus indicating that a quench of about 0.040 or so being good. Opinions on this (from what I have read only) with regard to turbo engines seems to contradict this n/a convention as a requirement to improve octane tolerence. I haven't studied this, it's an 'observation', maybe someone else will chip in, but I would opine that what holds up in a n/a motor should have a basis for consideration in a forced inducted one also.
Where I'm trying to get to here is piston selection with regard to pin to crown height. A lot of aftermarket pistons have a smaller pin to crown dimension, necessitating milling the deck more to achieve optimum quench, piston selection will affect how much you need to mill the block to achieve your desired piston to deck dimension whilst factoring in the thickness of the head gaskets you will be using. (Reducing strength and rigidity)
Obviously rod length options with these is pretty limited (none) and offset grinding the crank journals and using undersize big end bearings isnt really an option to play with. But if strength (of your stock block) is your ultimate objective and if quench on these things has any importance (my opinion above) a thicker deck and custom piston (smaller diameter for thickest wall thickness) would have some benefits. Like everything in life compromises have to be made and money is a factor to most of us on here. I hope at least the first part of my post will help some.
The rest I suppose is purely a personal subjective opinion.
![Quickstop [UK]](/data/avatars/m/5/5165.jpg?1570199786){kind=avatar}
