More heater output questions, 83 Ur-q

[David Ritter <dritter@mich.com>]

Hello,
I've been thinking about my low heat output in 0 F temps with the 83
Ur-q. I have already changed the heater core and hoses, so I think
those are ok, although I skipped the heater valve. I decided to pick
up a heater valve this morning, and change it out as soon as the temps 
reach 15 F or so around here. Working below 10 degrees just isn't all
that much fun in my book.
After I brought the valve home I noticed that the valve never reaches
what I would consider fully open. The valve seems to be designed to
restrict the flow somewhat. Question is, what is the reason for
restricting the flow on wide open heater? Is the core not able to
handle full flow? Does increasing the "wide open" flow by modifying
the valve cause other problems? Has anyone run with a pipe in place of 
the valve in really cold weather to see what would happen?
I am seriously considering modifying the new valve, since its not all
that expensive and our weather isn't exactly balmy these days, but I
would appreciate input on possible negative outcomes.

Thanks,

David