Jeff and I are working on a low cost water neck for
RX8 slide throttle engines. There is a limited
clearance between the RX8 front cover coolant inlet/outlet
and the slide throttle so we are using a relatively short
radius 1.5" ID  pipe bend. 1.5" inch ID hose is required
to get the volume of coolant flow high enough to transfer
heat from the metal around the combustion chamber to
the coolant. The thermostat is removed for the same
reason.

The billet pressure cap holder is off the shelf mass
produced part as are all the low cost hose barbs
from McMaster Carr.

It will look something like this. Not in its final
form yet as we are adding a steam vent line
and a cabin heater return line.

There is also some room for two small temperature sensors
namely temperature of coolant out of the block and
temperature of coolant into the coolant pump. Those
are handy for checking the efficiency of your
cooling system. There will also be room for a coolant
system pressure tap.

Those sensors can be installed
by the buyer by drilling the block with a the appropriate
size tap drill and taping the block for the sensor threads.
This will keep the cost lower for those people that don't
want or need all those sensors.

Paul Lamar