how much over would one have to bore out each cylnder to get a cumulative volume of at least 3.5 liters?

and would it be safe to do so?

2mm overbore (94.0mm final bore size) with stock stroke will get you 3497 cc's.

Safe? No idea. Have the machine shop sonic check your block.

2mm = 0.07874
I don't know of many blocks, even the older thicker blocks of high hp engines, that could take that much of an overbore.
0.040 is where most want to stop cutting.
0.060 is really pushing it.
0.080? Only after the above mentioned sonic testing and even then I don't think I would.

quote Originally posted by AL87: how much over would one have to bore out each cylnder to get a cumulative volume of at least 3.5 liters? and would it be safe to do so?

From a 60⁰ 3.4L engine (which actually is closer in displacement to 3.35L before rounding up), for you then "to get a cumulative volume of at least 3.5 liters", my calculations also show each cylinder needs an overbore of about 0.080 inches, or 2mm.

Safe or not (and I'd think not), perhaps an equally important question is determining where one could easily find off-the-shelf pistons to accommodate so large an overbore in the first place.

The non-VVT 3.5 litre pushrod blocks are 94 mm, btw.

The 3.9 and VVT 3.5 blocks are 99 mm.