Hey guys sorry if this seems like a stupid to some of you but I am trying to gather as much information as I can. One day I will attempt to build a engine..

So my 350SBC has the standard bore of 4.0 inches. And I am seeing pistons that say they are 4.030 inch bore. Does this mean I would have to get my engine bored out .030 in?

Also if I dont want to bore out my engine what size pistons should I be looking for?
(Engine will be a mild street engine that I can drive but still has a small amount of juice)

 

Yes that is correct, to a point.

That bore dimension is "nominal"... an approximate description, at best. Modern pistons and bores require a tight fit with little room for error, and not all so-called .030" overbore pistons require an exactly 4.030" bore.

Figure out what your goals for your motor are, THEN what pistons are appropriate to that goal THEN have your competent local racing machinist match the bore dimensions AND FINISH to the needs of the pistons and rings that support your goal.

 

There are spec for boring that leave enough cylinder material to finish hone to the correct size required for the pistons used. Hypereutectic pistons are a tighter fit than forged pistons and the machine shop should know what to bore and hone the cylinder to for the piston used. If the machine shop isn't buying the pistons the the owner usually brings the pistons to the shop or at least the piston part number and specs.

Back in the 90's the shop that honed the Pontiac block for my GTO numbered each forged piston and honed each piston to each bore by hand using tape gauges (long feeler gauges) to nail the fit. No one does it that way anymore though. Everything is expected to have much better accuracy these days and the shops just bore and hone to fit. New hypereutectic pistons are fit <0.002" from the cylinder wall.

I guess what I'm saying is you should be talking with your machine shop for this. I'm sure they want your pistons to fit also.

 

I would also add:

The odds that you can take some random block with some random # of miles and then replace the stock pistons with some random other ones and it all actually fit and work right the best it can, are somewhere between slim and none. Especially if it's a block from before about 1990.

Meaning, if you want a motor that runs RIGHT and doesn't smoke and doesn't puke oil out of every gasket and seal and dipstick tube and breather because of blowby into the crankcase, and otherwise runs FAR WORSE than it would have if you'd just left it alone, you'll want to have it bored out. .030" is the usual and customary "first scheduled maintenance" typically done to one. For best results, have it done with a torque plate, which simulates the stresses (changes in dimensions) from bolting on the heads. You might be amazed at how severely the bores change when those bolts get tightened. That means in turn, DO NOT have it done by whoever quotes you the cheeeeeeeeeeeepest price: that GUARANTEES it won't be done this way.

And no, don't worry about "stupid"... we all started out as beginners at one time or another. Far better to ask a question even if the answer seems obvious in retrospect, than to screw something up or get ripped off.

 

+1 on this. Or to put it another way, the only stupid question is the one not asked.