Thanks Bill, can you get Jon to chime in or post his data?

Bill,
I think this is a very significant issue since the 4100 is so popular and we are trying to sort out and document these pieces of American history!
I have no stake in the matter - I don't care what the 4100 cfm is, I'm just trying to figure it out.

The 600cfm seemed high to me, even before I saw Bob Sprowl's tests - consider the following:

The 2100 2v 1.08 is rated 287 cfm at 3.0 in Hg, which is 203cfm at 1.5 in Hg using the usual 1.414 conversion factor.

The 2100 2v 1.14 is rated 300 cfm at 3.0 in Hg, which is 212 cfm at 1.5 in Hg, same correction.

The 2100 2v 1.21 is rated at 351cfm at 3.0 in Hg, which is 248cfm at 1.5 in Hg, same correction.

Now I admit, these 2100 x 1.08 and 2100 x 1.14 numbers dont even make sense to me - seems like too small a difference between them.

But if we now consider adding a 2100 2v 1.08 and a 2100 2v 1.21, we should have close to the flow of a 4100 4v 1.08 x 1.19, right? So adding 203+248=451cfm, I'd expect the 4100 4v 1.08 x 1.19 to be close to that.

If we add a 2100 2v 1.14 and a 2100 2v 1.21, we should have a healthy approximation to the 4100 4v 1.12 x 1.19, right? So adding 212+248=460cfm, I'd expect the 4100 4v 1.12 x 1.19 to be close to that, 600cfm seems way high.

With all that said, the 4100 is a very smooth design - but still, shouldn't the corrected 2v cfm ratings jive with the 4v cfm?

If the 4100 1.12's really flow 600cfm that would be great news for a lot of us, we are just anxious to see some data either way.

I learned on the 4100, well, ok right after I learned on the Zenith 1 (our Model A had a Zenith 1 and our brand new 63 Merc had a 4100) and I think very highly of the 4100, it just seems there is a chance here to document everything and clarify this important issue. Thanks for the help this is a great site!