Secrets of maximum emissions legal horsepower.

Besides being an illegal modification, removal of a catalytic converter is just as likely to decrease horsepower as it is to increase it. It's true that most original equipment converters create enough exhaust system backpressure to adversely affect performance and overall engine efficiency, so a straight pipe in place of a catalytic converter would appear to be the optimum configuration for maximum power.

But appearences are often deceiving. Computerized engine management systems are precisely calibrated to deliver optimum performance with an exhaust system that offers some amount backpressure. When backpressure is all but eliminated, air/fuel mixtures can easily become too lean to allow an engine to produce maximum power. Virtually all electronic engine control systems automatically adjust fuel flow to precisely maintain the chemically ideal air/fuel ratio of 14.7:1. However, automatic fuel adjustment only occurs during part throttle operation. Major exhaust system modifications-- such as removal of catalytic converters-- often requires reprogramming of the engine control computer to reestablish optimum air/fuel ratios at wide open throttle.

Each vehicle has its own unique computer controlled air/fuel calibration so each responds somewhat differently to removal of a catalytic converter. Consequently, removal of a converter can result in a performance gain, a performance loss or no change at all. The question is, why contribute to dirty air and risk of a potential fine? Installation of a SuperStainless catalytic converter will allow an engine to produce maximum power while remaining emissions legal.

Exhaust system tuning is another phenomenon that impacts power output. In some dyno tests highly modified engines have actually produced slightly MORE horsepower with Random Technology converters than with an open exhaust - even though air/fuel ratio was optimized for each test. This unexpected bonus is the result of the same tuning effect achieved with tubular headers of a specific length. Installation of a catalytic converter in a full length open exhaust pipe defines the "end" of that pipe, effectively shortening it. The resulting impact on exhaust system acoustic waves and resonance can actually improve efficiency thereby resulting in a slight, but measurable power increase.

Obviously, your mileage and horsepower may vary, but the point to remember is by using high efficiency catalytic converters, an engine will produce maximum power while remaining emissions legal.

Catalytic Converters- The Inside Story

They’ve been cursed, damned, gutted, removed and praised, and depending upon your priorities, they’re either the best or worst thing to happen to automobiles in the past 30 years. Since they first appeared on 1975 model year vehicles, catalytic converters have made a significant impact on both pollution and performance. Unfortunately, that impact hasn’t always been positive on both accounts. Owing largely to early designs, which were very restrictive, catalytic converters are widely viewed as horsepower killers. And while even the most free-flowing converter will increase exhaust back pressure, the effect on performance can be minimal. Independent dyno testing has repeatedly proven that most engines produce just as much power when equipped with high efficiency catalytic converters as they do when running through straight pipes. So it just doesn't make sense to drive a car that isn't emissions legal.

That statement may seem to fly in the face of reality but catalytic converters have changed dramatically over the years. The first converters to find widespread usage were filled with pellets coated with precious metals. As hot exhaust gases pass over the pellets, (also called beads) their coating serves as a catalyst and instigates a chemical reaction intended to transform exhaust pollutants into harmless compounds. Specifically, when unburned hydrocarbons come in contact with platinum and/or palladium, the resulting oxidation process transforms them into carbon dioxide and water. Similarly, when carbon monoxide meets palladium and/or rhodium, the resulting oxidation process converts it into carbon dioxide.

"oxygen is as fickle as Lady Luck"

Initially, catalytic converters addressed only hydrocarbons and carbon monoxide. But oxides of nitrogen constitute another compound that fouls the air we breathe and in the early 1980s, rhodium, another catalyzing agent, was incorporated with the resulting converters being known as “three-way” because they address three, rather than two pollutants. Rhodium functions as a reducing, rather than an oxidizing agent. In “chemistry speak” that means it separates oxygen from a compound instead of adding oxygen to it. Consequently, nitrogen oxides are broken down into nitrogen and oxygen. However, oxygen is as fickle as Lady Luck and tries to dance with any available partner. In the exhaust stream, that’s usually carbon monoxide, which the footloose oxygen atoms convert to carbon dioxide.

Loose oxygen also combines with unburned hydrocarbons in the exhaust stream, so they’re fully oxidized before exiting the exhaust pipe. In theory, with a properly functioning catalytic converter, and an optimized air/fuel ratio, all potentially harmful pollutants are converted to nitrogen, oxygen, or water vapor. However, a number of other compounds found in fuel and air don’t participate in the catalyzing process, and pass through the converter unchanged.

"pellet-type converters being very restrictive..."

From an emissions control standpoint, converter construction is of little consequence. However, pellet-type converters being very restrictive to exhaust flow, impose considerably greater power losses than monolith-type converters. With its honeycomb construction, a monolith substrate consists of a number of relatively small “tubes” or cells through which exhaust gasses pass. The size of the cells and their length determines the amount of restriction and to some degree, the extent of catalyzing action.

The most influential component of the catalytic reaction is the “loading” of the washcoat that’s applied to ceramic substrate. Heavier concentrations (loadings) of the precious metals that cause catalytic reactions increase the effectiveness of the process, with no increase in substrate surface area. Rhodium, platinum and palladium, which are used in various concentrations in the washcoat, aren’t bargain basement metals, so converter manufacturers must tradeoff cost and effectiveness to produce converters that meet operational requirements, yet are affordable.

Most converters produced in recent years contain two monolith "bricks" spaced several inches apart from each other. The washcoat on the forward brick typically contains rhodium which causes nitrogen oxides to break down into nitrogen and oxygen. After passing through the first brick, exhaust gasses pass through an air chamber before entering the second brick. In some converters, known as “oxidation” types, a small tube passes through the chamber and injects air pumped in by an engine-driven “smog pump”. (In some vehicles, the "smog pump" incorporates an electric motor, which reduces accessory drive complexity and also allows for remote mounting.) Injected air simply brings additional oxygen into the exhaust stream to assist in the oxidation process.

"a catalytic converter should last the life of a vehicle"

Although “three-way plus oxidation” type converters were prevalent during the 80s, that’s no longer the case. With improvements in washcoat technology, and improved control of air/fuel ratios, the need for additional oxygen has been eliminated. Some vehicle manufacturers have continued to use oxidation converters on some models, but typically that has been done to use up inventory. As an example, the Corvette and Camaro Z/28 were equipped with oxidation converters through 1991 and 1992 respectively. But when the LT1 engine replaced the L98 (1992 in Corvette, 1993 in Camaro) three-way converters with no air tubes were incorporated.

In theory, a catalytic converter should last the life of a vehicle; it has no moving parts, the bricks are not consumed by the catalytic reaction and the cases of all original equipment converters are made of stainless steel, so rust isn’t a problem. In the real world, an excessively rich air/fuel ratio, oil or antifreeze in the exhaust system or physical damage can send a catalytic converter off to the great recycling yard in the sky.

Physical damage is the easiest to diagnose. If a converter is bounced off a curb or speed bump, or is struck by freeway flotsam, the ceramic bricks can be fractured. Once that happens, it’s just a matter of time before the bricks start rattling around inside the case, beating themselves into oblivion.

"Extremely high temperatures can result in destruction..."

Fuel, oil and antifreeze cause a different type of brick destruction. Under normal operating conditions, the catalytic process doesn’t begin until temperatures inside a converter reach 500 to 600 degrees (F). If air/fuel ratio is on target, and the exhaust is free of contaminants, internal converter temperature stays at about 1200 degrees. But when unburned fuel enters the picture, temperatures can reach 2200 degrees and either burn the precious metals out of the washcoat, or literally cause a melt down of the bricks. Extremely high temperatures can also result in destruction of the mat that's wedged between the bricks to the converter case.

Oil and antifreeze also cause elevated temperatures, but as the converter tries to burn (oxidize) these compounds, a residue, which plugs up the bricks is formed. At this point, the converter not only looses its effectiveness, it also becomes very restrictive to exhaust flow, which kills horsepower.

"...many times a high converter isn't quite what it seems"

When a replacement converter is required, a high flow model is the typical choice if performance is a consideration. But many times a “high flow” converter isn’t quite what it seems. According to Clay Ingram of Random Technology, "Replacement converters aren’t subject to the same requirements as original equipment models, so most standard replacement converters offer increased air flow potential. The 'high flow' label is a result of this increased flow capacity. However, a replacement converter designed for use on a four-cylinder engine will likely not have as high a capacity as an original equipment converter (with the same size inlet and outlet pipes) designed for a V8. Although converter manufacturers certify each converter type for a maximum engine displacement and vehicle weight, some dealers have no qualms about ignoring certification criteria. If a “high flow” converter has an extremely low price, chances are it’s not really a high flow model. Additionally, if a converter is installed on a type of vehicle for which it wasn't designed, it may not be very effective at controlling emissions."

Obviously, the bricks within a converter create the major resistance to exhaust flow. Over the years, various brick densities have been used, with the most common now being 300 and 400 cells per square inch. All other dimensions being equal, converters with 100- or 200-cell densities offer improved air flow capacity, but reduced emissions control efficiency. In many cases, it's necessary to significantly lengthen a 100 cell converter to achieve the necessary levels of pollutant control. That additional length reduces flow capacity, so it's possible to end up with a 100-cell converter that does not flow as well as a 300-cell model.

"maximum air flow capacity"

But another factor, and one that’s often overlooked, is brick length - longer bricks offer higher flow resistance. On the other hand, if a brick is too short, it won’t offer sufficient area to effectively control exhaust pollutants. Converter manufacturers use different precious metal loadings of washcoats and vary them according to brick length and density. Since all catalytic converters must meet standards established by the Environmental Protection Agency, (EPA) their efficiency in controlling exhaust pollutants is a given - provided a particular converter is installed on the type of vehicle for which it was designed. However, the super-cheap models typically don't have enough high quality materlials to allow them to be effective much longer than the EPA-required 25,000-mile emissions compliance warranty period. Random Technology converters are specifically designed for maximum air flow capacity and to remain effective well beyond the warranty period.