X2On forced ind. stuff I tell guys that they have a better chance with the 4.5 bore and keeping head gaskets in one piece. The next available "shelf" gasket over 4.53" is 4.64". IMO it's better to stick with a little smaller bore and keep some gasket material between the cylinders, unless you're going all the way to 4.60 bore.
I don't have a problem with the 4.375 stroke as long as you're willing to invest in the best, full kick out, full feature oil pan you can get, or go dry sump. As far as rods, the longest one you can afford. If you want a 6.385 rod you could go with a 1.27 piston, (JE Inverted dome 257942) shave a little off the top, run it a little out of the hole and run a thick head gasket. If you had a true 9.8 deck and took .03 off the piston, you'd only be out of the hole .013" which is easy to make up with a gasket. Truth be told, though, that extra 16ci over the 540, with twin turbo's, wouldn't be worth all the trouble. You can make just as much power with the 540 with a few more pounds of boost and a LOT less hassle.Im good with that didnt want to bigger than 4.5 anyway.
What stroke and rods work best?
the more cubes you have the more turbo you need for a given rpm range.for a turbo build no way I'd use the 4.375" stroke, ..
back it off to the 4" and use the heavy duty stuff like Mrdragster said.
Typically in the limited tire stuff I work on, x275, 10.5 ect, they benifit
from the shorter stroke, little less torque, quicker spool and more
manageable power curve to get it down the track.