Demon carb questions

[rolling_Thunder]

Anyone on here know much about Demon carbs? (Prior to them being bought out by Holley)

I came upon a matched pair of Demons I will be running and am attempting to determine what I can as the owner didn't know too much. I have determined they are Mighty Demon cars of either 850 or 950cfm. The Race demons have removable boosters which these carbs do not so they would be Mighty Demons... the throttle bores are 1-3/4" so that puts them at the 850/950 cfm rating... the secondary side of the body have a "42" case adjacent to the venturi openings....

Previous owner has already drilled and tapped some some fittings to boost reference the primary power valves (I assume)

Anyone know how to determine the cfm rating from anything beyond what I have listed?

 

[Raymond Murray]

You need to measure venturi diameter to get the answer (its the smallest diameter in the main body where the booster sits). You don't need boost reference PV's unless you are using a turbo/supercharger/etc.

 

[rolling_Thunder]

Well It is difficult to measure the venturi size accurately with the calipers i have but I am coming up around ~1.41"... so not too sure if that puts it closer to 1-3/8 or 1-7/16 but definitely under 1-1/2" so with a 1-3/4" throttle bores I would imagine that would definitely put it down on the ~850cfm rating... I have found a 950HP holley is 1-3/8" venturi and a 1-3/4" base plate but actually flows ~830cfm

These are older Barry Grant Demons so they are not as clearly marked like the newer Holley made Demons.

The boosted PVs will come in handy... (roots blower)

 

[33 IMP]

I've got a gold claw RS (prehistoric demon) with 3sets of sleeves, so I did some research.
Red sleeves, 1.400 venturi x1 11/16 bore, rated 750 cfm.
Blue sleeves, 1.425 venturi x 1 3/4 bore, rated 775 cfm.
Gold sleeves, 1.500 venturi x 1 3/4 bore, rated 825 cfm.
If you are around 1.400 with a 1.3/4 throttle plate, those are likely 750
A holley 4781 850dp supposed to have a 1.56 venturi.

 

[beanhead]

The "42" stamp indicates a 1.42 venturi. I'm struggling to remember the old BG numbers book but I believe the older non-removable sleeve 1.42 x 1.75 carbs were rated at 825 cfm, and wet flowed closer to 900cfm. Two of them? Should be plenty!
If you get a chance post up some pictures.

 

[Raymond Murray]

The dimensions are close to the 950 Holley #80498 which are 1.376 X 1.750.

 

[33 IMP]

The dimensions are close to the 950 Holley #80498 which are 1.376 X 1.750.

Isn't that the carb that holley CALLS a 950..... but is really the exact same dimensions as a 750? My 4781s are "850" cfm, and considerably bigger venturi than that.

 

[rolling_Thunder]

Isn't that the carb that holley CALLS a 950..... but is really the exact same dimensions as a 750? My 4781s are "850" cfm, and considerably bigger venturi than that.

Yes - what I got was they put a 750cfm body on a 850-950 baseplate with their 1-3/4" throttle bores and they flowed ~830cfm... that's what I found on the net (for what its worth)

So 1.42" venturi sounds about in line with that i measured. These apparently were on a blown big block Ford in a boat and the owner upgraded to larger units.

This will be going onto a mild 440 with a roots blower (6 or 8-71) for a little street engine... so already being boost referenced is kind of a plus - just wanted to make sure these were not obscenely oversized. I was going to run some 750 holleys but these basically fell into my lap.

So a little more digging and I believe you're right on - these appear to be Mighty Demon 825cfm carbs. Kinda obscure as not much information is out there as far as factory jetting or air bleed sizes... almost like Holley bought the brand to shrink it then kill it off.

 

[33 IMP]

......."kill it off" Ding ding ding!