I am doing a 305TPI to 350TPI swap and noticed that I had 2 knock sensors in my 305 one in the bottom right of the block and another on the back of the left head... considering that Im using my 305 heads do I need to replace both knock sensors with 350 sensors or leave the head sensor a 305 and swap the block sensor? it makes sense to swap both with 350 sensors but then again Im confused why I have two knock sensors... thanks in advance

Are you sure the sensor in the head is not a coolant temp sensor or sending unit?

positive because the coolant temp sensor is in my intake and the sensor in the head looks alot like a knock sensor

I believe what you are seeing in the head is a cooling fan switch. It has the same connector on it as the knock sensor does.

Yeah, fan switch! I just dealt with them on my heads, just forgot for the time being. One side head has the coolant fan switch, the other head has the coolant sending unit for your dash gage or dummy light.

If you do go with aftermarket heads make sure they have the ports to accommodate the sensors. The Canfields I got did not. Luckily the TPIs BigMouth manifolds have an extra port in the intake for one of the sensors, the other, I put inline of my coolant bypass hoses to the heater diverter valve.

Correct, that is a fan switch. The connector is similar to the knock sensor - don't get them mixed up.

There are 3 coolant "sensors" - the coolant temperature sensor on the intake manifold, the temperature gauge sending unit in the driver side head, and the radiator fan switch in the passenger side head.

Thanks for everything guys. I just looked in my almighty chilton =P and saw that they do look the same lol good thing I asked because I would have ended up spending money on an unnecessary sensor and had cooling problems when I finally get everything in it =P hopefully only a couple more days... Just got the last of my parts in from summit =D

Thanks guys