Parts / Product Profiles

The New Demon Carburetion: Bringing More Power to the Street and Track

We’ve seen these new carburetors up close and we’re very impressed with them. All models benefit from uniquely contoured throttle entries and smooth, concentric venturi bores (no more ridge lines to obstruct airflow!) for improved power output without sacrificing everyday drivability. Plus, every made-in-the USA Demon carb is wet-flow tested and packed with features like Max-Density™ cast metering blocks (Road Demon) or CNC-machined metering blocks with precision-drilled idle-feed restrictors and emulsion bleeds (Speed/Mighty Demon), high-flow fuel bowls with greater fuel capacity, non-discolorable sight-glass windows, 4-corner idle circuitry, power valve blowout protection, and a silver dichromate finish. Speed and Mighty Demon carbs also benefit from the exclusive Idle-Eze™ base plate, an ingenious device that allows quick and easy idle speed adjustment.

Demon engineers took these features and packed them into three distinct models—Street: Road Demon, Street/Strip: Speed Demon, and Race: Mighty Demon. When used as recommended, enthusiasts will be rewarded with increased performance, clean idle quality, and instant off-the-line response.

Road Demon
If you’re looking to wake up the dark side of a daily-driven hot rod or mild weekend cruiser, bolt up a Road Demon carburetor. These carbs have quick-change vacuum secondaries, a reinforced Max Density™ baseplate that resists ear breakage, down leg boosters, an electric choke, an integral automatic transmission kick-down mechanism, and a fuel feed line for easy installation. The vacuum-operated secondary throttle plates are ideally suited to engines coupled to automatic transmissions and stock to mild stall torque converters.

Road Demon carbs are calibrated for use on stock and lightly-modified six-cylinder and V8 engines producing up to 350 horsepower, with cam durations up to 220° (@ .050″). The Road Demon 625 is for engines ranging from 250 to 350 cubic inches; the Road Demon 725 is designed for engines displacing 350 to 500 cubic inches.

One Speed Demon feature that deserves extra attention is the billet aluminum Idle-Eze™ baseplate. It includes a specially designed air valve that allows you to fine-tune the idle speed by metering additional air into the intake manifold—avoiding the potential for stumble or reduced throttle response as engine rpms climb. The valve can easily be accessed through the air cleaner stud hole, and idle speed changes can be made quickly and accurately using a single screwdriver—perfect for engines with aggressive cam profiles.

Just like the Road Demon, vacuum secondary Speed Demon carbs are best suited for automatic transmission-equipped vehicles with low stall speed converters. Speed Demons with mechanical secondaries are for manual and automatic transmission-equipped vehicles with high stall torque converters operating at 2,500 rpm and higher.

The Speed Demon 650 is recommended for mildly modified engines displacing 302 to 427 cubic inches, and the Speed Demon 750 works exceptionally well on mildly tuned 427 to 477 c.i.d. engines. The Speed Demon 850 is well suited for use on mild performance big-block crate engines ranging in displacement from 488 to 540 cubic inches.

Mighty Demon
When a conventional carb can’t keep up, it’s time to step up to the biggest, baddest Demon of them all. For unrestricted airflow, Mighty Demon carbs have no choke horn. They also have replaceable air bleeds and idle feed restrictors, mechanical secondaries, and an Idle-Eze billet aluminum baseplate.

The Mighty Demon’s ready-to-run competition tune is perfect for high-compression engines with performance cylinder heads, a high-flow intake manifold, and extreme cam duration (up to 260° @ .050″). Choose the Mighty Demon 750 for a well-prepared 350 to 406 or a mild performance 427 to 468 c.i.d. engine. You’ll want the Mighty Demon 850 if you’re running a well-prepared, high output 440 to 540 cubic inch street or race engine.

There you have it—three new, high quality Demon carburetors. Add it all up and putting a Demon Carburetion Road Demon, Speed Demon, or Mighty Demon carburetor on your car is one of the smartest moves you can make to dramatically improve performance and drivability.

Parts List
Road Demon 
DEM-4282010VE: Road Demon 625 cfm, vacuum secondaries
DEM-4402020VE: Road Demon 725 cfm, vacuum secondaries

Speed Demon 
DEM-1282010: Speed Demon 650 cfm, mechanical secondaries
DEM-1402010: Speed Demon 750 cfm, mechanical secondaries
DEM-1563010: Speed Demon 850 cfm, mechanical secondaries
DEM-1282010VE: Speed Demon 650 cfm, vacuum secondaries
DEM-1402010VE: Speed Demon 750 cfm, vacuum secondaries
DEM-1563010VE: Speed Demon 850 cfm, vacuum secondaries

Mighty Demon 
DEM-5402010GC: Mighty Demon 750 cfm, downleg boosters, mechanical secondaries
DEM-5402020GC: Mighty Demon 750 cfm, annular boosters, mechanical secondaries
DEM-5563010GC: Mighty Demon 850 cfm, downleg boosters, mechanical secondaries

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  1. Keep in mind the cam and its idle/off idle manners is what drove alot of the design of these carburetors. The Idle-Eze feature is fantastic for people experimenting with different cams, as it saves drilling out butterfies as a fix for keeping engine vacuum applied to the idle port at idle. Bigger than 240 degrees @ .050, the Mighty Demon is worth looking at. Bigger than 220, the Speed Demon is a good starting point. The Road Demon works great for stock or something with a little extra in the 250 to 350hp range. These numbers aren’t written in stone, but are a good guideline. Alot of these old specs are not easy to find on Holley’s website today, and some things like the old Race Demon specs are nowhere to be found. If you own one of those, you are into tuning anyway, and don’t mind the time investment. Pick the right carb, and save yourself being forced to tune emulsion/air bleeds on a dyno, and know that alot of folks dinging Demon carbs didn’t do two things: pick the right carb, or disassemble/clean/inspect out of the box before firing up. Pay attention to your metering blocks passages and its ports, and all should be well.

  2. I have an 850 mechanical secondary speed demon on a 496 with about 650 hp and 241/245 duration hydraulic roller cam and was wondering if I should upgrade to an Annual discharge and anything else that you suggest. Id rather save money than chase 10 hp for $500+ bucks!

    • I heard that you can send your carb to bg with a hundred bucks and they would change it to annular, not sure if they still do that, but They used to.

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