IMO if you don't have the CR500 modification or are running a CR500 big bore kit when you
replace the rod on the crank you should be installing the 400 rod as a replacement, there is
no doubt that the 500 rod is a stronger and heaver rod but I see no need or advantage in
using the 500 rod (adding weight) I have never seen a 400 rod break I am sure they have
it just does not seem to be something that happens enough to seek out a stronger rod,
I have never seen a small end of the rod break or even have a bearing failure, I am
sure they have failed but I bet it was due to someone reusing the old bearing during a
top end rebuild, when I remove mine they look new and have no measurable wear,
they are tempting to reuse but I install new, there is less side clearance with the small
end of the 500 rod in the piston this might even limit or reduce the ability for the small
end bearing to receive lubrication and actually shorten the small end bearing life because
of the extra rod width shrouding the wrist pin and bearing.
1.6 ounces of weight don't sound like much weight but try moving 1.6 ounces up and down
80mm 133 times a second, I bet after a few minutes you would not want to carry the extra
weight, I see NO advantage only disadvantages in installing one in the 400 Engine, I would
say if you had a 500 conversion you need to run it, a common mod is to reduce the reciprocating
weight of a Engine,
Engine builders will lighten the rod and remove excess weight (grams)
from the piston to increase performance and extend it life (piston speed VS mass) so I might
install a 400 rod in my CR500 conversion and see how long it lasted, what I have seen fail the
most on the 400 rod is the bearing, I have never seen the big end of the rod break not to
say it has not happen I just see the weak part as the bearing and the bearing is the same
the 400 uses.