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The Brains of a Carburetor

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Posts: 317
Joined: Sun Dec 13, 2015 10:21 am
Location: Birch Run,Michigan

The Brains of a Carburetor

Post by NormS »

A carburetor is essentially a mechanical computer. For a carb to work well, there is a considerable amount of "pre-programming" that has to occur. One of the critical aspects of any carb is the booster signal curve. This is the vacuum that the booster generates, to pull in the main circuit fuel, measured through the usable airflow range of the carb.

Most carb modifiers, even though they have heard the term “booster signal curve,” do not know what it is, so they ignore it. A few have figured out how to measure it, but don’t know how to analyze their data mathematically to see how good or bad the curve is. Even fewer have figured out how to do the mathematical analysis. Very few have figured out how to modify boosters to make their signal curves follow the equation. Most modifiers assume that any booster in any venturi size has a manageable signal curve. Not so, not even close.

A booster’s signal curve is described by a mathematical equation. The signal curve of any booster can be analyzed mathematically to see how close it comes to the “perfect” curve described by the equation. Some of the stock Holley boosters have a near perfect signal curve, but only in a small range of venturi sizes. These boosters can be modified to have better signal curves over a wider airflow range. This is an important aspect in getting an engine to run well in a broad RPM range.

In 1985 I figured out how to measure and analyze booster signal curves, and started a long learning process on how to modify boosters to get better signal curves, and how to calibrate carbs for booster curves that range from near perfect to far from perfect. The “far from perfect” signal curves are usually encountered when racing class rules give you no choice of booster type, and allow few if any modifications. This learning process led to an understanding of how to modify boosters not only for better signal curves, but also for better carb airflow and fuel vaporization. It’s easy to modify boosters for increased airflow. It’s much harder to do that when you want to have a good signal curve and good fuel vaporization at the same time. At C.F.S., booster modifications are always done with all three of these factors in mind. The benefit of this approach is accurate control of air/fuel ratios over the entire RPM range of the racing engine. The result is more power, a broader power curve and safer engine operation. © Norm Schenck
Competition Fuel Systems Birch Run,MI. www.compfuelsystems.com/index.html 520-241-2787
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