source for aftermarket engine sensors? (temp, boost, pressure, etc)
 

I'm looking for engine sensors to use for datalogging. I'd prefer not to piggyback on the stock sensors.

I know some places sell sensor kits for ECUs (like Haltech) but do they publish specs for resistance values?

Another source I'm thinking of is replacement gauge sensors. I know there's no respect for cheap gauges like Autometer, but is it the sensor or the gauge unit (or both) that is inaccurate? If I buy a set of Autometer gauge sending units and datalog the outputs, will I get less accurate measurements than using say DEFI sending units?

I'm mainly looking for sensors for air temp, water temp, oil temp, boost pressure; maybe also fuel pressure, oil pressure and EGT. Hopefully with resistance specs, so I can translate the readings to real world values without having to calibrate the sensors myself.

Has anybody else bought sensors specifically for datalogging before?