Cam base circle question

I've received conflicting opinions as to my need for a small base circle cam on my 383 project. I was going to use a spare cam that I have lying around to use as a mock up to determine clearance.

My question: Is the base circle of all standard cams the same?

73 Mike said:

I've received conflicting opinions as to my need for a small base circle cam on my 383 project. I was going to use a spare cam that I have lying around to use as a mock up to determine clearance.

My question: Is the base circle of all standard cams the same?

Click to expand...

A standard base circle cam is appox. 1.190 and all the 383/s we build with 6 inch rods either the Procomp Scat with the 7/16 bolts or the Callies Compstar rods there always seems to be plenty of clearance as we use a 1.130 base circle cam on these builds with no problems.

Small base circle cams are near .900 inches. I've bought Crane roller cams as small as .890 They are a must when running 6 inch rods in stroker small blocks. when you get up to the 4.00 inch stroker cranks you also need to buy stroker clearanced rods.

Or swap to a smaller rod journal diameter w/ accompanying smaller big end rod, a small journal will give you more cam clearance, and for higher revs you get lower radial speed. A downside is reduced journal overlap but if you build that kind of stuff you can afford the appropriate crank.

A bit of a project update and my next question.

The pistons are in and the block clearances look ok, even if they make me nearvous. I used a piece of wire which measured .065 to verify that I had at least 50 thou from the piston bolts to the block. I've got it, but my goodness that isn't much space.:noworry:

I was going to use an old cam to verify that I needed a small base circle cam. I spoke to a few tech lines on Friday though and all suggested custom grinds based on what I was looking for. All three suggested small base circle cams since they don't cost any more anyways.

My question: Is there any downside to using a small base circle cam on my roller motor? I need to buy pushrods anyways so that isn't an issue. My lifters (Comp 818-16) say they are fine for small base circle cam. Anything that I'm not aware of?

Not really, the only thing to watch out for is that the lifter body oil groove does not drop out too much and is exposed, however usually that shouldn't be an issue. The only time it will be is when doing the 60 deg. V6 roller lifter retrofit.

Thanks TT. I wondered about that when I saw that there were some lifters specifically for small base circle cams. The spec says that it should be fine but I will check to make sure before I bolt on the intake.