I have two sets of heads for my 1957 cadillac . The one thing i know is that the engine in my car is out of a 1956 . The engine number tells me so . This is where i am confused . i have a cracked head on the engine . The heads that are on the engine require two different lengths of bolts. the bolts that are exposed next to the spark plugs are shorter then the bolts that are under the valve covers . The new heads that i purchased to put on the engine require all the same length bolts . the bolt holes that are exposed have bosses or standoffs on them ,keeping the bolt lengths all the same ,where the heads that are on the car do not have bosses or standoffs on them . requiring shorter bolts . Can anyone out there tell me what head belongs to the 1956 engine or does it really matter . Thanks Bill
Yes it does matter. The horsepower went from 285 to 325 HP from 56 to 57. This was due to an increase in the compression ratio from 9.75 to 10:1 . The Eldo's did even better on HP,but that was carberation.If the engine stayed at 365 cu in the increase in comp.was due to a change in the heads ,rods,pistons or crank. I checked only the heads changed.
To tell them apart without part numbers can be done with casting numbers. But I don't have a full list,so the other way is valve diameter. To do it this way you need to just measure the diameter of the heads of the valves. Measure at the point where the valve seats to the head, not the outer diameter of the forging. 1956 inlet 1 3/4 " ,exhaust 1 9/16" : 1957 inlet 1 7/8" ,exhaust 1 7/16".The 1957 exhaust being smaller seems odd since racers are always trying to make their engines breath better ,but I checked two sources and they agree.
Be sure you watch the the push rods and lifters on this engine. They were changed mid year 57 . It won't matter if you use early or late as long as you use pairs.Warren
It got to bothering me so I looked up how to measure the valve head. I was wrong. THe TRW book I looked at says to measure the whole forging not just the effective size as I posted earlier. Sorry Warren
Thanks Warren,
i will make sure i measure the valves , i know may engine is a 1956 engine . So i will check to see if the numbers you gave me match .
thanks again , Bill