So last question today. Again I have a 1974 455 that I am putting in a 1970 Cutlass Supreme and they are calling for 2 different heater control valves. Which one do I use?

 

I would suggest the heater control valve for the car its going into. Shouldn't it work with heater controls in the car to work properly ?

 

Correct, you need the valve that works with the vehicle’s system. Note the thread diameter is different between the 1970 and 1974 heater valves and intake manifold ports.

 

So i would need a pipe thread reducer to make that work Correct?

 

I used one of these.

 

Thank you for the info I apreciate it very much.

 

Your 70 requires a heater control valve that is normally closed and opens when vacuum is applied. The 1974 heater control valve is normally open and closes when vacuum is applied, so exactly opposite of what the car needs. And be careful if buying a new one. Like most Oldsmobile parts, nearly all of the vendor catalogs have these valves listed incorrectly.

 

Thanks Joe, you've been busy answering a lot of my questions today.

 

does any one know the size of reducer i need to put the 1970 valve in the 1974 intake?

 

3/4” outside diameter
1/2” inside diameter

 

Remember these are pipe thread sizes. Probably would be 1/2 inch pipe and 3/8 pipe thread, or 3/8 and 1/4 pipe.