The performance world is packed with thousands of ways to improve and reshape the power curve of your engine. Engine size, camshaft profile, compression, carburetion, and intake manifold design are only the beginning. The goals for better power are simple, yet the criteria complex. How fast do you want to go, what is your budget, and how will you be using your car? To engine builders these decisions ultimately define how well a street-performance engine will perform throughout the entire rpm range.
Selecting a carburetor that balances good performance and drivability for a street-driven car is a significant step. Don't make the mistake here of trying to copy what works well on your buddy's drag-race car. On the strip, a dedicated race car is set up to spend almost no time at low rpm (below 3,000). On the street, a typical performance car will spend most of its time operating from off-idle to 3,500 rpm, and on occasion past 6,500 rpm. Therefore, selecting a carburetor for a street-performance car is often more involved than choosing a carburetor for a dedicated race car. This is because the street engine must be built to operate under a range of performance conditions, varying altitudes, traffic, cold climates, and sometimes different drivers.
If the carburetor installed on a street engine is too large, the engine will generally be lazy until rpm exceeds 3,500 rpm. Contrary to popular belief, a larger carburetor allows too much air to enter the engine quickly without enough fuel, which creates a bog. Accordingly, the flexibility of engine operation over a broad rpm range will suffer. This is because as the comparative venturi size increases, air velocity decreases through the carburetor, forcing the carburetor's main system to postpone fuel flow until a higher rpm is reached. If the carburetor is too small, overall power may suffer because the engine can't draw in enough air and fuel to develop sufficient power.
For a closer examination of proper carburetor selection and what guidelines should be considered, we visited with the tech guys at Barry Grant, Demon Carburetion. The folks at Demon spend hundreds of hours a year taking phone calls and solving carburetion dilemmas. And while no two calls or applications are exactly alike, they have found many patterns and developed guidelines to help select and size your carburetor to match your application, maximizing the vehicle's performance.
Choosing the right carburetor...
Choosing the right carburetor depends on your engine power level, camshaft duration, the intake-manifold style, vehicle weight, transmission type, gearing, driving style, and budget. These three carburetors are Barry Grant Race Demons with mechanical secondaries and are designed for very high-end performance engines.
For most street-driven performance...
For most street-driven performance vehicles with smaller-displacement engines, carburetors such as the Road Demon (at 525-725 cfm) provide excellent drivability and good power. These also feature Max-Density Cast metering blocks with adjustable jets and four-corner idle, a billet baseplate, and sight glasses on the fuel bowls to easily set the float levels.