[FHC1971]

In my 1971 Firebird Formula I have the original intake manifold from the original YS motor. I am putting and original 1971 YS motor that I located. It is complete and un messed with. It came back from the Machine shop and I'm putting the final touches on it before going in my car. My original manifold takes a larger diameter thermostat than the motor that I'm putting in. The original motor was from California. The new motor is from Atlanta. Both are same cast numbers and within 7 days of each other. 3/10/71 & 3/17/71 Why are they different??