I was just looking at three different cams I have:
1. My original 1957 EDB with a #4 above it:
2. 1961 truck cam
3. A factory replacement cam which I believe from what I have read are like the 62-64 truck cams?
After doing some measurements the 57 EDB cam has a smaller base circle then the other two? Maybe there is something I don't know but I would have assumed the base circle would have been the same on all.

Maybe a regrind

I guess that's one possibility, I wish I had another 57 cam to measure.

As the lobe lift increases, the base circle of the camshaft decreases.  A .380” lift at the valve camshaft has the same lobe clearance at the cam bearings as a 0.600” lift camshaft.  To get more lobe lift, the base circle is simply decreased.
 

Lorena, Texas (South of Waco)

Thank you Ted, I think I understand what you are saying. So the 57 cam with the smaller base circle could be OEM?

Or it could have higher lift. To get the total lift, subtract the base circle from the total over the nose/base circle. All my non roller GMC6 cams are done this way. The military trucks had steel cams instead of case iron. And we are able to get almost .400" cam lift by the grinding. This multiplied by the rocker ratio can get you pretty total valve opening.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

Thanks, I did measure them this morning and got .270 on the 57 small base circle cam and .250 on the large base truck cam. So I'll be using the stock 57 cam on this engine, it's only going to be a back up. I have an Isky E4 in the engine thats in the car now.

The 1957 oem camshafts with their higher lobe lifts will be cut on smaller base circles than the 1954-1956 and 1958-1964 lower lift camshafts.  If you end up measuring the base circle on the Isky camshaft, you’ll find that it’s even a smaller base circle than the 1957 grind and that’s due to the additional increase in lobe lift.

Lorena, Texas (South of Waco)

Now that I understand the base circle I'm sure my E4 does have a smaller base circle, I would have liked to measured it just for curiosity but it's been in the engine for 3 years. I'm just an old shade tree mechanic and had never measured a cam before, I guess I have too much time on my hands but it was great to learn something new. Thank you Ted.

 Like  Ted was saying  The reason the  wilder can is cut that way is  if the  lobe was made larger there would be a point were they cam wouldn't fit into the block!  I have a ,780 lift cam for a Cleveland that the back side of  lobe is the same size as the shaft itself