VETDRMS

I have been fighting some idle/part throttle issues with my Mighty Demon 750 and after many phone calls to BG and 3 carbs later they finally fill me in on a little info.

The "750" rating is just their for comparison to the holley equivelant. Venturi size is similar ect, but the Mighty Demon 750 flows 952 CFM!

The 650, which he said I should be running actually flows 750 CFM.

Obviously for my 406's requirements 952cfm is on the upside.
The solution i've yet to try is locking out the timing and getting rid of
my open plenum spacer.

To me its settling to finally get an answer on that one.

:cheers:


[Modified by VETDRMS, 12:50 PM 3/24/2004]

1Bad69

any idea what the speed demon 850 flows?

Corvette_fetish

WOW, That's good to know considering I might get a Demon.

Solid LT1

I'll sell you one of BG's Claw carbs (same as the Demon but, Holley sued him in court and he lost so he had to go to the Demon type carb.) The Claw I have is a 650 double pumper with a choke housing but, no choke blade in it. I had an off idle mid range stumble that was sloved by going back to my old standard: a $100 swap meet Holley #4777 with a cut off choke housing. $295 for the Claw, my Holley=PRICELESS! not for sale, it's one with a good fuel curve! my engine seems to like.

bhmyers

Yea, I have heard the same about the 750 Demon, I couldnt get my mixture set right until I spoke to BG.

442olds

I would like to know what test pressure they were checking that 750 at to get 925. Also is that 925 wet or dry. That does make a difference. All holleys are rated at 1.5"Hg. So if you test a holley at 1.5"hg and a deamon at 1.5"hg what do you get, probably 750 as it is rated. So the holley to will have an increased flow rate at whatever test pressure Grant is using. What that flow rating will be would have to be tested.

Also I doubt that 925cfm is wet. See if he'll give you that number. Also ask if they are just testing one venturi and multipling by 4. This is a number that is totally bogus. Flowing all four barrels at the same time is the only way to get a truely accurate flow number out of the carb. Most places don't have a flow bench powerful enough to flow more than 500 cfm at 1.5"hg, so they test only one barrel and multiply by 4, which is very very wrong.

VETDRMS

442olds I am pretty sure he said it was at 1.5". I did not ask about if it was done on a single venturi.

I personally would assume BG would have the correct equipment, and if they were trying to market that idea as a selling point they would advertise it.
However, I could be totally off base, your questions most likely have some validity to them.

I will make it a point to ask a few more questions when I call them back.

Thanks!

:cheers:

VETDRMS

bhmyers Did you end up locking out the ignition advance? What did you do to resolve it?

Thanks!

442olds

I don't still sounds a little fishy to me. Why advertise a carb at 750 when it flows 925! Really makes picking the right carb a little more difficult. Grant has become a huge company in the past few years and are legions away from a specialty carb shop anymore. Cranking out cookie cutter carbs to the masses. They do have improved castings over the standard holley, but holley has come back with the hp series main body to stay competitive. Even holley's will vary from batch to batch as would Grant carbs I would suspect. The only true way to make sure your carb prefroms as rated is to have it prefessionally modified to do exactly what your engine calls for, but add the cost of that on top of a $5 to 600 carb and that gets pretty pricey, so we rely on a system of numbers put in place a long time ago. And now Grant has messed that system up with his 925cfm 750!

I may have to call my freinds at C&S Specialties and see if they have tested any of the demon carbs. I am sure they have. You want a real carb tuned to your application, they are the place to go. http://www.candsspecialties.com They were actually involved in the suit of Holley vs. Grant since they are one of the top Holley Carb Tuners/Modifiers. I think their biggest split dominator flows 1400cfm through two barrels wet!

MotorHead

I have heard BG carbs flow more than they are rated many times, the only reason I can think of that they don't call a carb that flows 925 a BG 925 is they want people to compare a 750 Holley and 750 BG and when you make more power with BG everyone thinks the carb is better :D

killervette666

i had the same thing told to me when we bought a 750, we later returned it and got a 650 in exchange, the fact that it flows better is good, its just that you have to compensate for the higher flow numbers by getting a smaller carb.

cardo0

Well how about thier annular discharge booters ? When the say thier carbs flow more with the same venturi means to me thier venturi entry and exit and everything in between produces less restriction to airflow .
I'm no expert on carbs but some of the biggest advances have been in the boosters becoming sensitive to very small pressure drops accross the carb. Which means the annular boosters will still flow fuel with a good enough mix at low flows.
So what I'm saying is I expected the Demons to flow more than a stock Holley the same venturi size. Just expected it to mix even better while allowing more hp/breathing/rpm.
So that my 2 cents and take for what its worth as I felt nothing said here was unexpected. :hat

Pete79L82

When Holley first started rating their carbs, they listed everything with a 1.280 venturi and a 1 11/16 throttle plate as a 650cfm, with a 1.400 venturi and a 1 11/16 throttle plate as a 750 cfm, ect. regardless of what it actually flowed. The rest of the indudtry has just followed along to make it easier to compare carbs. Since they now have castings with the choke horns removed and the inlet radiused the carbs flow a lot more but are still rated the same.

Monday I did some dyno tests on a couple of different carb for a customer. We tryed thre different carbs by differnt manufactures. All were listed as 750 cfm models. All were race version carbs. They were all on the same engine with no other changes made other than jetting for best power. the results were:

Race Demon . 536hp @ 6400 -- 481tq @ 4800 -- 769.6cfm @ 7500rpm
*****'s WW .... 554hp @ 6600 -- 487tq @ 5100 -- 768.9cfm @ 7500rpm
BLP WW ....... 559hp @ 6600 -- 492tq @ 5200 -- 771.1cfm @ 7500rpm

As you can see they all flowed more air than they were rated at. The Race Demon and the *****'s carbs had radiused venturi inlet castings, the BLP had the standard main body casting with the choke horn milled off. They all flowed within 2.3 cfm of each other but you can see that there was a considerable difference in power. 23hp and 9tq diffence in just a carb change. On a race motor that is huge!

This is not to say that one manufactures carb is better than anothers. On a different motor with a different heads/cam combination the test could be completely different.

VETDRMS

First let me say (in jest), that it appears that some forum members are dyslexic: All the responses are referring to 925cfm when I stated 952 in the post.. I just found it funny, not to offend anyone. :)

Pete79L82

Thanks for the great info! :cheers: That is quite a HP improvement between carbs that flow nearly identical.

Cardo0 They don't use Annular boosters on the Mighty Demons (save for one). They are Downleg
:smash:


[Modified by VETDRMS, 9:52 PM 3/24/2004]

71coupe

What kind of part throttle problems are you having - what speed & gear?

Never Finished

Where is Lars? He can make some sense of this. I'm amazed at his posts.

BB wowbagger

:iagree: :lurk: :cheers:

gkull

It's always been obvious to me that the 750 Demon had to be flowing more air than a Holley because look at how much bigger jet size you have to run in the BG line of carbs.


Don't lockout you timing! Get your distributer recourved for a smaller total mechanical advance. My Mallory is set to 16 degrees of advance. So i set the initial at 16 degrees without the vacuum advance hooked up. I have the 16 mech. advance all in at 3000 rpm for a total of 32 degrees (Dart Heads only require 32 for max power)

I also drilled out my Demon squirters from a stock of something like .034 to .045 so it gives it a big fast squirt on any throttle change.

Boofers

The larger the carb the higher the airflow must be before the main metering system kicks in. If the carb is too large, or if your cam is really big resulting in your engine vacuum at idle being very low, the pump shot will be consumed before the main metering systems kicks in. This results in a sag or bog in the off idle transition. Sounds like you need to richen your idle mixture. Thats my $0.02 hopefully you don't offer me change... :cheers:

Eric R

:iagree: And the larger the carb the greater the chance of going lean due to the fact that the airflow is not great enough to properly pull from the boosters. I can see that the next post will suggest a longer pump shot, and bigger jets. This will help but it is just a work around to cover the problem.