Re: [Chrysler300] CARTER AFB Capacity Calcs

[Paul Holmgren <paulholm@xxxxxxxxxxxxx>]

Richard Barber wrote:

> I received or retrieved the information below from some one, sometime and
> warn that it is not consistent and may result in more inaccuracy being fed
> into the system.  That being said, I have played with the data and converted
> the 625 cfm carb primary venturi to 1/5/16" for consistency and determined
> the chart is based on about 100 cfm per square inch of total venturi area.
> I think several of the bore diameters are off, also, but I believe nominal
> carb capacity is more likely to be based on venturi area.  

> I'm working on a pair of Carter 2444S/2445S carbs for a '56B and the
> venturis are both stamped 1 1/16" and the throttle bores all measure 1
> 5/16".  Based on the four 1 1/16" venturi openings and the nominal 100
> cfm/square inch of venturi area, each carb might be rated at 355 cfm.  The
> 354 cid '56B engine requires 533 cfm at 5,200 RPM at 100% volumetric
> efficiency or about 75% of the total air capacity of the two carbs.  Seems
> reasonable.  533=(354 X 5200)/(2 x 1728)

> These are the same carburetor dimensions specified for the 1955 331 cid
> C-300 engine.  Interestingly enough, the New Yorker and Imperial single four
> barrel carburetors also had the same dimensions (and jets) according to the
> specifications in the 1955 Service Manual.  So, adding the second carburetor
> doubled the nominal air capacity, although the requirement only went up 13%
> (from 4600 RPM to 5200 RPM).  Those two 2317S's or the 2444S/2445S pair
> should really feed those old hemi's.  The net effect would seem to be a
> slightly higher manifold pressure at any given throttle opening due to the
> velocity being halved by the addition of the second carburetor.  And, that's
> a good thing for more power, but bad for power brakes.  Anyone heard of a
> reasonable or rated redline for the 1955 300 and/or NY engines?  Are these
> six-grand engines in stock form?

> A possibly helpful hint for calculating total venturi area: (This gives the
> area for two venturis-D is in inches)
> Primary venturi area:  1.57 X D squared 
> Secondary venturi area:  1.57 X D squared
> Add the two values above to get the total venturi area per carburetor,
> multiply by 100 to get an approximate carburetor air capacity in cfm.

> I know there are some other engineers, mathematicians and technicians out
> there who will check my calcs and I hope they do so.  If anyone has
> comparable capacity data for new or aftermarket carbs with specified venturi
> diameters it would be interesting to see how they stack up against this rule
> of thumb.

> C-300'ly,
> Rich Barber
> Brentwood, CA
> 1955 Chrysler C-300

I was told years ago that the 57 carbs are rated at 385cfm each.

AND old Hot Rod math said that with a 2x4 setup you add both then multiply by 
.75 to get the total of both.

I also remember reading that rating carbs by CFM is a later method AND not the 
one used by Chrysler to calculate the requirements for their specifications for 
the carbs they bought to use.  I seem to recall that they used a pounds per 
minute method.

ALSO, thru many years of wandering the swaps looking for a set of 57 carbs I 
have come to the conclusion that Chrysler bought larger carbs for the 300's then 
GM or Ford ever did in that time frame for any of their cars. So I used the 
'peek down the venturies' as a quick first look before thinking about a closer 
examination to see if they might be Mopar WCFB's.
This explains the strong desire by some of those spending vast sums of $$ for 
2x4 carbs for their GM resto's, buy the Chrysler carb and make it work on the 
small block chebby cause it preforms better then the one's GM specified.
(reinforeced by the open offer from a well known Vette Dealer to buy any and all 
Chrysler spec'ed WCFB carbs I choose to sell to him, either the single WCFB or 
any from a dual setup)

-- 
Paul Holmgren
Mine: 2 57 300-C's in Indy
Hers: 05 PT GT R/T HO Stage 1
Hoosier Corps L#6


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