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Demon Carburetor - The Demon Within

This Line Of Fuel Meters Helps Brings Out The Beast In Performance

Mike Petralia May 1, 2001
Sucp_0105_01_z Demon_carburetor Carburetor 2/15

Even though a carbureted vehicle hasn't rolled off the assembly line for more than a dozen years, that in no way means that carbs are dead. Nothing could be further from the truth. In fact, GPT300, formerly BG Fuel Systems, has capitalized on the carburetor power market and has engineered some of the coolest street and race carbs on the planet.

Sucp_0105_03_z Demon_carburetor Demon_rs_line 3/15

The Demon RS line of performance carburetors is the first to offer a vast assortment of user-friendly tuner parts.

The Demon carburetor line is made up of four models: Road Demon, Speed Demon, Race Demon, and King Demon. The Road Demon carbs flow 625 cfm and are engineered for street performance with vacuum-operated secondaries. Road Demons are engineered as an affordable fueler for 200 to 350hp street engines. Speed Demons are next up the performance ladder and are available in 650, 750, and 850-cfm versions that can be ordered with either vacuum or mechanical secondaries.

The newest carb to come from GPT300 is the Speed Demon VE that even offers an electric choke (the only 850-cfm electric choke performance carb in the Demon line) for the ultimate in streetability. The Race and King Demon carbs can be used on the street if you're so inclined, but they're really built for all types of racing from off-shore power boats to Pro-Street race cars. Race and King Demons are offered in two versions, Standard and RS. The RS in all Demon carbs designates that they are equipped with removable venturi sleeves and replaceable venturi boosters which give these carbs the ultimate in versatility and tuning ability.

Sucp_0105_04_z Demon_carburetor Color_coded 4/15

Customizing your Demon carb is easy thanks to its removable venturi sleeves. The sleeves are color-coded for size and offer cfm variances from 390 to 1,050, meaning you can have anything from a restricted Winston Cup-style four-barrel to an all-out, nitrous-ready monster just by purchasing one carb.

Looking beyond race tuning and ultimate horsepower capability, the Demon line was engineered with several improvements over tradition four-barrel carbs. One of the line's best features is the billet aluminum baseplates on all Road, Speed, and Race Demons and the aluminum metering blocks standard in all. The benefit of using billet material over a casting is that there's no porosity in billet parts and porosity has been known to cause havoc in carburetors. Also, making the base plates from a solid block of aluminum means there's little chance of snapping an ear off of it when you torque it down to the intake manifold. Idle and float level adjustments are easily done on the Demon carbs thanks to the large, clear sight-glass plugs in the side of each fuel bowl and the big, knurled idle-mixture screws that are easy to keep your screwdriver or fingers on. Race Demons even feature a secondary throttle shaft idle speed adjustment so motors with big cams won't have to open the primaries too far just to idle. All Demon main bodies are manufactured utilizing a new die-casting technology that ensures an accurate, smooth venturi that won't require any hand polishing to optimize flow. This means the days of grinding and smoothing venturis are a thing of the past.

The Road and Speed Demon line were designed to handle about 90% of the carburetor market. We've had good success making power with out-of-the-box Demon carbs, including the stock 750-cfm Speed Demon that fueled our 408-cid "Mean Little Rodent" big-block, which has already made more than 540hp with nothing more than a jet change. In fact, the Speed and Road Demon carbs are so universal and cover so much ground that you'd be hard-pressed to find a street engine they wouldn't work great on.

Sucp_0105_05_z Demon_carburetor Ve_series_carburetor 5/15

The new Speed Demon VE-series carb offers all the creature comforts and streetability you'll need in a performance carb. Adjustable vacuum secondaries and an electric choke are available on all the 650, 750, and 850 cfm VE carburetors. These carbs were engineered to deliver exceptional starting and all-weather driving performance.

Race Demon RS carbs are the first carburetors to feature unique removable venturi sleeves and boosters. What this means is that with the purchase of just a single carburetor, you'll have the option of building anything from a 390-cfm oval track carb to a 1,050-cfm heavy-breathing monster for all-out competition. Also, the billet aluminum metering blocks used in all RS Demons feature removable emulsion circuit bleeds allowing you to fine-tune the fuel curve to match the engine. Although, modifying the emulsion circuit is best done on the dyno and does require intricate carburetor knowledge. But, changing venturi sleeves does not require intense wisdom, and it's easy to do with just a few hand tools in about 30 minutes. Basically, tuning any performance carb properly does require a good understanding of how and why a carburetor functions. That's why GPT300 recommends running your new Demon carb right out of the box to see how it responds before you turn a single screw.

If you've chosen your carb properly, you'll have some idea of where and if any changes are needed. And if you get in too deep, there's always a carb expert waiting on the phone at GPT300 (at least from 8-5 EST M-F) to get you out of trouble should you tune beyond your means. To further assist you in your quest to perfectly tune your new Demon carb, the original factory settings for each carb model are printed in detail in the back of the Demon catalog. And since there's never any drilling or machining involved with tuning a Demon carb, it's always easy to return to stock if your modifications don't pan out.

With companies like GPT300 perfecting its Demon line of street and race carburetors, we're sure to have four-barrels under the hoods of our hot rods for years to come.

Sucp_0105_07_z Demon_carburetor Removable_venturi_boosters 6/15

The RS Demon's venturi boosters are also removable. Old carburetor designs required epoxy to hold the swedged boosters in place so they wouldn't fall out when subjected to harsh racing vibrations. The Demon boosters utilize an ingenious double-locking design, with the booster held in place by the venturi sleeve and locked down with a nut that can't fall out when the metering block is in place.

Venturi Color And Size

All sizes shown are in inches
Color Venturi size Baseplate Airflow cfm
Orange 1.064 1 7/16 390
Green 1.280 1 11/16 675
Red 1.400 1 11/16 775
Blue 1.425 1 3/4 825
Gold 1.500 1 3/4 975
Black 1.562 1 3/4 1025
Silver 1.590 1 3/4 1050
Black w/ annular boosters 1 3/4 750
Silver w/ annular boosters 1 3/4 950

By The Numbers
A carburetor's metering block can intimidate even the most die-hard car buff. We thought this would be a good time to enhance your carburetor vocabulary and educate you in the inner working of the four-barrel. Note: most of the descriptions we've included here pertain to all carburetors using replaceable metering blocks.

Demon carbs utilize the tried-and-true, power-valve-enrichment circuit that we're all accustomed to. GPT300 incorporates power valve blow out protection in the entire Demon line. The tiny, pressed-in check ball is shown here in the black 1 3/4-inch RS Demon baseplate.

A new die-casting technique is used to produce smooth, concentric venturis in all Demon fuel meters. No longer is it necessary to hand polish the carbs to achieve maximum flow. This 1,175-cfm RS King Demon is ready to race, right out of the box.

If you're going to upgrade your carburetor, you should seriously consider upgrading what feeds it as well. This is the BG 220HR fuel pump and bypass regulator that's designed to flow 220 gph continuous on the street. It would also make a great street/strip fuel supply and we know of at least one 10-second car running this as its sole pump.

Carburetor modifiers like Barry Grant used to get lots of money for installing modified boosters in carbs. Now the tuner can swap boosters in minutes on all RS Demon carbs. Annular, dogleg, and straight boosters are all available. The annular discharge booster shown here pulls a strong signal and can make great power when combined with the black or silver venturi sleeves. It's too big to use with any of the smaller sleeves.

1.Accelerator pump fuel discharge
2.Power valve channel restriction (PVCR)
3.Idle fuel enters here (from main jet)
4.Idle fuel travels up idle well here
5.Emulsion hole #5
6.Emulsion hole #4 (not present or may be plugged in other carbs)
7.Emulsion hole #3
8.Emulsion hole #2 (not present or may be plugged in other carbs)
9.Emulsion hole #1
10.Siphon break keeps boosters from flowing fuel at idle
11.Bowl vent
12.High speed bleed air enters here
13.To booster venturi
14.Idle fuel mixes here with air entering from No. 15 (replaceable jet pictured here in RS models only)
15.Air from idle bleed enters here
16.Emulsified idle air and fuel go to idle mixture screw here
17.Tip of idle mixture screw is visible in this hole (fuel goes to idle discharge slotin base plate from here)


GPT300 Inc.
Dahlonega, GA 30533



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