[Gooserider]

I wouldn't expect there to be a big difference in head losses from different I/O locations. No matter what the location is, for most of the tubes they will have to make at least two right angle turns at each end; one to flow along the tank, and one to go from the tank down the tubes. An end or face I/O has the same turns. A side I/O does have the advantage of flowing along the tanks so you get rid of one bend.

I am not sure how much restriction the I/O - tank bend actually causes, since it is fairly large radius and the tank is larger than the I/O fitting. I suspect it is only a tiny fraction of the total for the entire rad.

Likewise, the difference between same corner fittings and opposite corner fittings is something I suspect might be mostly theoretical. In an opposite corner design, the distance between the I/O fittings is the same for all tubes, so all should see the exact same flow. In the same corner design, the distance varies from tube to tube, and in theory the shorter distances ought to get more flow. In practice however, I suspect that the tubes are restrictive enough that the difference will probably be negligible since the input tank would be supplying roughly the same amount of overpressure to all the tubes.

All else being equal, an opposite corner, side I/O rad (2-553?) might be best, but one would have to be very careful that the losses from any added plumbing or bends needed to deal with the I/O location doesn't amount to more than the gains. I think one is better off sticking to an I/O location that is easy to plumb, which is why I (and lots of other folks) choose the 2-342 for it's opposite corner face I/O design.

Gooserider