Will I need to use a 1/2" NPT to 3/8" adatpers for the fan switch and CTS? Kevin Gray says he had to use them on his 86 IROC. He also said using them prevented him from splicing and lengthning the connectors. What have you guys that alreadt did this swap use? Did all the sensors screw right in w/o adapters?

 

Just look at the hole in the casting, and the threads on the sensors... if the holes are ½" NPT and the sensors are 3/8" NPT, then you'll have to use bushings. No biggie.

Those of us with early model heads have to do the same thing. My fan switch and gauge sending unit have bushings.

Home Depot has them, for about $2 apiece. Not something I find particularly significant on the grand scale of things, as I'm doing an entire intake system or head swap, but certainly worth preparing for in advance. I hate standing there at 2 in the morning, all ready to pour water in, except that I have a 3/8" thing in my hand and a ½" hole in the motor..... wrong time to discover that.

 

I can't comment on the fan switch as mine is on the pass side head, but the CTS will screw right in on the hole next to thermostat housing.

 

Both coolant holes in the HSR manifold are 1/2NPT. One is for the heater hose nipple & one for the CTS. A 1/2NPT to 3/8NPT bushing is needed for the CTS.

edit I just checked the car the hole on the drivers side next to the water outlet is 3/8NPT & is for the CTS. The 1/2 NPT holes are for the heater hose outlet & sender for the gauge. At least thats how mine is set up, since my AFR heads have no sender holes in them.

 

Just noticed you (as well as everyone else it seems) have 3 coolant ports and mine came with 2. I do not have the 1/2 NPT port that is on the front of the intake. It's not drilled or anything. I just have the one 1/2 NPT port on the right side and the 3/8 NPT port on the left. Even the GMHTP article shows the third port.

Not a big deal really as I have the temp sender on the drivers side head.

Just wondering if Holley forgot to drill and tap this port?