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BEGi Rising Rate of Gain Fuel Pressure Regulator


The BEGi model MR2035 rising rate pressure regulator was designed and developed by The Bell Engineering Group, Inc., by none other than forced induction guru Corky Bell. Among many other things, Corky Bell has authored a great book on the subject of turbocharging called, "Maximum Boost: Designing, Testing and Installing Turbocharger Systems." I would strongly recommend anyone who is interested in the subject of forced induction to read this book.

But what is the rising rate regulator and what does it do? To answer that question, let's look at a typical electronic fuel injection system for a gasoline engine. A typical EFI system utilizes an electric fuel pump which runs constantly. The fuel is sent to the fuel rail. On the other end of the fuel rail is a fuel pressure regulator, which bypasses a certain amount of fuel back to the fuel tank in order to maintain a constant fuel pressure in the rail, as set on the regulator. This allows the fuel injectors to vary fuel mixture just by modulating the pulse width of the injector.

There's one problem with this concept though; in a gasoline engine, the pressure in the intake manifold or inlet ports, where the injectors are located is constantly changing, based on rpm, throttle position, and in the case of the turbocharged engine, boost pressure. Manifold pressure can go from, say, 25 inches of vacuum (negative pressure) all the way up to, say 15 psi of positive (boost) pressure. Even though the pressure in the fuel rail is constant, the injector is "seeing" varying pressures in the manifold, therefore the effective pressure at the injector can fluctuate, which would make the fuel injection system unstable and unpredictable. For example, let's say the pressure in the fuel rail is 30 psi of fuel pressure, and the pressure in the manifold is at 0 psi. Pressure at the injector would be 30 psi. However, let's say that the turbo is producing 5 psi of boost pressure. Now, the injector pressure would only be 25 psi, and, in effect, the engine would be getting less fuel at a time when it needed more fuel.

To overcome this problem, most fuel pressure regulators are "manifold referenced." This means that there is a signal line from the manifold to the regulator that tells the regulator what the manifold pressure is, and actually causes the regulator to adjust fuel pressure to compensate for changes in manifold vacuum or pressure. A manifold referenced regulator always provides a 1:1 change in fuel pressure as related to manifold pressure, and are extremely common on fuel injected engines.

The rising rate of gain fuel pressure regulator takes this concept a step further, and it would generally be used in a situation where an electronic fuel injected engine is retrofitted with a forced induction system, either a turbocharger or a supercharger. A rising rate regulator, in theory, would allow one to add a turbo system to an existing fuel injected engine without altering the fuel injection maps at all. Here's how:

We know that a gasoline engine runs a fuel mixture of between 15.5:1 (lean mixture) to around 11:1. (rich mixture) The electronic fuel injection system is programmed to operate the engine within this range, and the mixture is programmed to vary based on engine rpm and load. However, when forced induction is added, the mixtures across the rpm and load map must change. An engine with forced induction must run richer mixtures across the board, when operating under boost. The reason is that compressing the air produces heat, and heat leads to detonation. Richer mixtures keep the combustion temperatures down which prevent detonation. One way to change the mixtures for a forced induction engine would be to change the fuel maps. However, this requires special software, an engine dyno, and a high level of skill and experience in tuning engines. The rising rate pressure regulator was developed as an alternative to complicated and expensive re-mapping of the EFI control. Instead of changing the injector pulse widths, the rising rate regulator increase the fuel pressure as turbo boost increases. It must increase fuel pressure at an exponential rate to boost pressure, not at a 1:1 rate as a normal, manifold referenced regulator would do.

The MR2035 model regulator would go in place of the normal pressure regulator. It would be set with a "base pressure" that would be equal to that of the normal pressure regulator, say 30 psi. A signal line would come off the manifold to the rising rate regulator. When the system is operating off boost, it acts just like a normal manifold referenced regulator, providing a 1:1 relationship of fuel pressure to manifold vacuum. With the engine idling, fuel pressure would be 30 psi or less. But, as the boost pressure would begin to rise, the pressure signal will cause the regulator to switch into rising rate mode, which means that it would begin to increase fuel pressure at an exponential rate. There are three adjustments on the MR2035. The first is the base fuel pressure, which is the normal off-boost fuel pressure. The second adjustment is the onset of gain, which sets the point at which the regulator switches over from 1:1 operation to exponential operation. The unit can actually be set to switch over while still under slight vacuum, increasing the flexibility and control of the unit. Finally, the third adjustment is the gain adjustment. This adjustment changes the rate at which the fuel pressure rises, and changes the shape of the fuel pressure vs. boost pressure curve. This allows the tuner to control the level of enrichment that is provided as boost pressure increases.

In conclusion, the BEGi MR2035 Rising Rate of Gain Fuel Pressure Regulator provides a simple and inexpensive way to change the fuel mixture curve of a forced induction engine without having to alter the EFI maps. It is particularly useful on a naturally aspirated engine that is converted over to forced induction.

For more information, go to: http://www.bellengineering.net/Pages/products_FPR.html


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