Harold...
A few months ago you had recomended a cam to me, and before I purchase it an important point was brought up to me. The cam you recomended was the 401B4LUN. My question is in a 406 or a 421 what base circle will be needed? Are they the same or what do you suggest for each? Would there be any harm in getting a cam with a base circle for a 421 cid and running it in a 406, if I decide to go this route?

With long rods, 5.7" or longer, the 406 base circle is .100" smaller in diameter, generally around 1.030". The base circle for the longer crank is generally only about .030" smaller than that. Steve and Mike know what size you will need. All you need is the correct lenth pushrod to go with your base circle size.

UDHarold

Are there any issues with getting one with the smaller base circle just to be safe that everything will clear as I am not 100% sure which stroke I will be going with, in case I stay with a stock stroke?

Talk to Steve about timing change caused with smaller base circle. He may recommend the next size up to keep the duration the same at .200" lift. Steve and I went through this earilier this year and I feel that it is something that should not be overlooked. This change in timing, evidently, applies to all cams, not just Harold's, when you grind to a base circle that the cam was not designed for.

That being said, the shape of the lift curve is probably more important than it's duration, but my 501C2 lost 4.5 degrees @ .200" going to a .900 base circle. This is something that Steve, Kirk at Bullet, GOSFAST, and I all agree on. That, in itself, is a pretty powerful statement.

I'm mentioning this because it think it bears considering when you go to a SBC. Knowing this "going in" avoids any surprises when you measure you cam timing.

Talk to Steve about timing change caused with smaller base circle. He may recommend the next size up to keep the duration the same at .200" lift. Steve and I went through this earilier this year and I feel that it is something that should not be overlooked. This change in timing, evidently, applies to all cams, not just Harold's, when you grind to a base circle that the cam was not designed for.

That being said, the shape of the lift curve is probably more important than it's duration, but my 501C2 lost 4.5 degrees @ .200" going to a .900 base circle. This is something that Steve, Kirk at Bullet, GOSFAST, and I all agree on. That, in itself, is a pretty powerful statement.

I'm mentioning this because it think it bears considering when you go to a SBC. Knowing this "going in" avoids any surprises when you measure you cam timing.

=
This is correct & it works both ways when using the lobe specs from any cam grinder unless they are using the new generation of CNC grinders like Harold is.
With these all this can be designed into the grinding process.

A lobe designed for a small block ground on a BB core will grow.
A small base circle will shrink the lobe as measured at specific points.
Another thing that effects what you get from a master is the size of the wheel being used to finish the cam.
If it is different than the master was designed to be used with the lobe will change slightly too.

To answer the question though,, I would prefer to stay with the largest core possible as they are more "stable" with regards to cam & ignition timing.
But no, there are no real issues going to a smaller one except what Ken just mentioned with these types of milder cams.

A bigger core is always a better thing with aggressive cams but doesn't do you much good if it won't fit in your engine :D

If you are considering going to a stroker get the small base circle with most rods.

In other words, you guys all agree that lobes don't ratio big base circle to small base circle!

I woulda thought they would have..

Very interesting..

Thanks..

pdq67

i am also very suprised by that. i guess you learn at least one new thing everyday! i try to learn more every day but that isnt what i was expecting. thanks for the info guys

67