Thoughts on Demon carb?

Discussion in 'Classic Mustang Specific Tech' started by mrmustangman357, Dec 14, 2007.


  1. htwheelz67

    htwheelz67 Member

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    question to tech@BG, I hear different things but if a 750 flows around 900, what does a 750 annular flow? and if an 850 flows around 1000 then what does an 850 annular flow? If you did use too big a carb say if a 750 mech sec was optimal would using an 850 annular with vac secs hurt or help power and drivability?
    #61
  2. D.Hearne

    D.Hearne Banned

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    That's what's not uniform about that formula. It's only useful in helping choose a basic size carb for a given engine displacement, it's far from being the final answer in what's best for your combo & application though. If you want a good street carb with throttle response and mileage in mind, you can't go wrong with a smaller size than the formula tells you, that and in a a vac sec carb as well. If you're looking for track only like drag racing, a bigger carb (or in my case CARBS:D ) maybe what you want. In my case with the 331, I've got the best of both worlds. Excellant mileage, Fantastic throttle response and enough cfm to feed the monster with the 3x2's. The only drawback was the cost, I bought the whole setup second hand, 1 year old for $1100. (intake, carbs, linkage and air cleaner assembly) I think this setup was up to $1500 last time I looked on Mustang's Unlimited's site. The main reason I went with the 3x2's was the sound eminating from under the hood at WOT with the windows up...........................STEREO !!!!!!!!!!!!!!!!!!!!!!!!!!:hail2: :hail2: :nice: :rlaugh:
    #62
  3. Tech @ BG

    Tech @ BG New Member

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    The 750's will flow around 920 and the 850's a little over 1000. No official numbers right now on the annular stuff but the 750 annular will flow just a little bit more than our 650 which flows 753. If you put too big of a carburetor on an engine you have several issues.... they will tend to be rich at idle no matter how they are tuned and go lean at wot. A lot of guys call in with too big of a carb and want to put "smaller jets" in it thinking that will make it smaller. Say they have a 850, they ask for "750" jets. As most of you guys already know it doesnt work like that and taking jet out of a carburetor that is rich at idle already is just going to lean it out worse when the carb is too big. It will also hurt the power and drivability as well.
    #63
  4. Tech @ BG

    Tech @ BG New Member

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    Exactly and it is real easy to pick the wrong carburetor just by using the formula. We still get a lot of guys who want to argue the point when asking for carb recommendations though because some of the other companies still promote that theory real hard.
    #64
  5. D.Hearne

    D.Hearne Banned

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    One question: do ya'll sell a lot of your 3x2 setups? Only seen em advertised in a couple places. Seems to me the price tag would be a turn off to most though. It was a good grand higher than the Mustangs Unlimited repop setup.
    #65
  6. Tech @ BG

    Tech @ BG New Member

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    We have sold several hundred of them since they were released. I have one myself on a 65 fastback. They are priced higher than the stock stuff but they are also far superior. The original stuff has what I call the coat hanger looking linkage for one where ours has all nice stainless rod with rod ends and joints. Throttle works a lot smoother and it's safer. Our carbs also have billet metering blocks and baseplates and flow better than the original Holleys do.
    #66
  7. 10secgoal

    10secgoal Active Member

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    Hmm, getting ready to stop using Holleys right here. Never had a problem with it on my own stuff. But it seems about 40-50% of holleys I've put on in the last 2 years have flaking problems. Pulled apart another one the other day, 3 months old and you can see the flak all over the inside of the bowl. It's becoming stupid now. Getting real tired of it.:mad:
    #67
  8. Tech @ BG

    Tech @ BG New Member

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    I'd be real careful if you have some flaking. Not sure if I had posted the link to this on here but definitely worth checking out.


    http://www.uscgboating.org/recalls/recalls_detail.aspx?id=070045T

    and

    http://www.holley.com/HolleyNews/Volvo Penta Carburetor Recall.asp
    #68
  9. JC6715

    JC6715 Member

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    Same here man, I started having fuel delivery issues after having the Holley carb on for maybe two months, pulled the bowl off and it looked like someone poured a bottle of very course metal flake into the bowl... Luckily Summit was great about replacing the bowl no questions asked at no cost to me...

    I am definitely going with a Speed Demon for the new engine build...
    #69
  10. D.Hearne

    D.Hearne Banned

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    Not sure about the original linkages, but the repop stuff is trouble free. As for flow, it's got enough for the 331 it's feeding. A $1000 price difference is far and away, way too much to ever let me think about switching.:rolleyes: "billet" never did impress me.
    #70
  11. Tech @ BG

    Tech @ BG New Member

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    The billet isn't really for "looks" but rather because you get a better quality part. Our metering blocks are hidden by the fuel bowls so you dont really see them. A nice advantage of the billet parts though is that you dont have to worry about porosity in the castings. Our carburetors have other benefits as well like clear sight glasses for adjusting float levels and screw in air bleeds for tuning if needed. I am not sure on the factory Ford vs our but I do know when we tested our carbs against the Pontiac factory tri-power stuff it was good for 65 hp on a little over 400 inch motor. I forgot to mention earlier but our Mustangs Unlimited does sell our package as well as the one you mentioned. What did you end up using for an air cleaner on yours?
    #71
  12. Tech @ BG

    Tech @ BG New Member

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    Here's a pic so you can get an idea of what the linkage looks like.

    Attached Files:

    #72
  13. Tech @ BG

    Tech @ BG New Member

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    Here's the one on mine with a few small changes for the nostalgic look. The air cleaner top looks all gold but all of the ribbing and lettering[raised area] has been polished. It's in a GT350 Hertz clone so wanted to tie the top in with the gold stripes on the car.

    Attached Files:

    #73
  14. D.Hearne

    D.Hearne Banned

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    I've used a K&N filter in it, both with the stock height (1.8") and a taller 3" K&N. To use the 3" I fabricated a reversed base to move the filter forward for firewall clearance. That was when the motor was in my 89 Ranger. I now have the motor in a 77 Comet and was thinking on doing the same thing. The setup fits under the hood with the shorter filter, but I'll have to reverse it again to clear the rear bracing at the rear of the hood, then cut the hood to allow the filter to poke thru. Going to cover it with a Comet GT scoop. Hard to tell, but your's looks like the air cleaner assembly is also reversed as compared to mine. It's covering the distributor more like when I reverse mine. The 1.8 K&N is p/n E-1960, the 3" is E-1963
    #74
  15. Tech @ BG

    Tech @ BG New Member

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    The bottom is a factory Thunderbird 3-2 bottom which sets the air cleaner further forward than the one we supply with the kit in the other pic. The top is a Cobra 2-4 with a pair of fabricated studs. Car is under construction right now as you can tell but I'll post some pics of it later with the air cleaner as shown in the other pic. In addition to the one pictured with the oval billet air cleaner we offer a "old school" version too which has 3 individual air cleaners, red fuel lines going to a chrome distrubution block and the carburetors are more of a traditional "gold" color. A lot of guys are using that version on the street rod stuff.
    #75
  16. D.Hearne

    D.Hearne Banned

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    Interesting about the T-Bird bottom. I wonder if it uses the same factory top, just reversed ?
    #76
  17. Helmantel

    Helmantel New Member

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    Maybe an even better comparison is the intake port volume of heads. Different heads can have the same intake port volume (say 160 cc) and would therefore be considered suitable for a certain type of engine (say a 302) and performance goal. Yet the heads have different flow numbers.

    Like with intake ports, it's the flow velocity rather than the flow capacity that makes a carb or head suitable for a certain engine. The flow velocity is largely determined by the dimensions (port cross area, throttle blade size....) which makes both carbs/heads suitable for the same engine, yet the flow capacity of one head/carb can be better than the other.

    At least, that's the way I see it.

    A question for the Demon Tech: Would it be possible to use Holley bowls on the Demon carbs? Call me weird, but although I like the design aspects of the Demons, I care more for the classic Holley look. Not that the Demons are ugly, but I just like the 60's look better.
    #77
  18. Fast63

    Fast63 New Member

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    I have a question for Tech @ BG, I have a 650 Speed Demon that I bought used from a buddy of mine and it needs a rebuild, mainly the floats because they have been stripped at the locking nut. What part number rebuild kit do I need and where can I get it? The carb is about 4-5 years old now.
    #78
  19. Tech @ BG

    Tech @ BG New Member

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    When you are referring to the "floats because they have been stripped at the locking nut" are you describng the needle and seat assembly or the bowl? If it is the n/s assembly those do come in a rebuild kit. The kit number for a mechanical secondary carb is 190004 and the vacuum secondary carb is a 190003.
    #79
  20. Tech @ BG

    Tech @ BG New Member

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    There are several fitment issues that does not make this a viable swap. The other issue is our bowls are larger and hold more volume and this coupled with the different sight location can affect the calibration.
    #80

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