072 and new BigBoy

4 1/4 on the inside?  Maybe.  On the outside it would be fatal, but BB overhang is not that bad on the inside.  It will be close.  Worst case, you may not be able to run something on the inside track while running the BB on the outside.

You should consider 081 pr 096 outside. I have 096 and 099 and the over hang is 2-1/2 inches....wow..This Big Boy will be Amazing!!! Give this monster some space...

Lee,  the 072 is on the outer loop so I hope it will clear other 3 curves have 51/2" center to center rail.
$oo

Leapinlarry,  I cannot go any bigger if I could I would go the biggest curve available.
but 8' rooms are all I have so 072 it is.
$oo

Is that a Scale Big Boy or a traditional one?

I now have one of each and the Scale one Requires O-72 MINIMUM.

I'm pretty sure that goes for all makes of the Scale version.

The Imperial Railking one will run on insanely tight curves (O-31) but looks very odd doing so. It also has 4" overhang to the outside on said tight curves (Why it looks wrong) Inside overhang is under 2" but best bet is to lay out a couple curves at your desired spacing and put the equipment on them. Move them back and forth and ensure a minimum of 1/4" gap exists, thains rock a bit when running so 1/4" may or may not be enough gap.

I prefer a minimum of O-48 for my Imperial Big boy and the new layout will have easements to O-72 at the tightest on the mainlines so I can run the Scale version.

to clarify I have all the clearance I need on outside of 072 curves.
My question is will 4 1/4" from center rail of 054 to center rail of 072 be okay?

the other 3 curves are 5 1/2" from center rail of 054 to center rail of 072.

I hope this clarifies my question in case I didn't make it clear the first time.
Thanks for all replies so far.

$oo