What sensor is this? Knock sensor, water temp sensor?

I am about to put my new heads on, but there are no holes drilled for this sensor

 

I believe thats the water temature sending unit that goes to the temp. gauge in the dash.

 

Water temp for the guage is on the drivers side head, fan switch is on the pass side head, and the knock sensor is in the coolant drain hole in the block, right near the starter.

If theres no spot for that in the head, then you can put that one in one of the holes in the intake manifold.

 

Such as where? I just want to make sure I am rigging this right.

 

thermostat housing for example

 

No, I wouldn't suggest putting it there, because then it won't read the engine temp before the thermostat opens. What happens if the thermostat sticks? The engine will burn up and you'd never know.

Most aftermarket intake manifolds will have a few spots to put your heater hose fittings on the front coolant passage where the thermostat housing is cast. One on the passenger side, and one on the drivers side. You should put your heater hose fitting (or a plug if not using the heater) on the passenger side, and the temp sensor in the hole on the drivers side.

This pic shows both holes on the front of the intake, on either side of the thermostat housing location: