If I remove the thermactor air compresor unit, will the engine run ok without it?
Do I have to block the exhaust coming out of the manifold?

 

If you have factory cats in the long run you're better off leaving it running to prevent your cats from clogging up. If propely removed it won't affect engine running, for example by plugging the back of the heads and removing/ plugging all vacuum sources.

 

Why do people want to remove this? It doesn't really add to the back pressure, does it? And it shouldn't really be much of a load in the serpentine belt, it's just a little air pump.

 

I went with aftermarket cats on my true dual setup and the air pump was no longer needed, that's the only reason I removed mine