Common misconceptions as perceived by ANDIAL

Question #2 ~ I am looking for additional performance and see that there are a lot of aftermarket chips available. These chips seem to make a lot of horsepower. Are they any good, and are they something you sell?

Chips (or E-PROMs) E-PROM stands for "Erasable Programmable Read Only Memory." This is a programmable microchip. Removable chips were used on all Porsches from the 1984 911 through the 1995 993. Beginning with the 1995 993 B-Turbo and the 1996 933 Carrera, the chips are integrated into the DME unit (Digital Management Electronics) and are no longer easily removable.

Basically the chip has two primary functions:

To control the fuel delivery through fuel mapping.
To control the ignition functions, including timing, through ignition mapping.

The factory programs these functions to provide the best operating results over a wide range of operating conditions. The design is therefore somewhat of a compromise. Changes to these functions enable the tuner to make some subtle changes to the engine performance. The emphasis here is on subtle. Don't be misled by the outlandish horsepower claims that you hear and read about. If you do nothing else to the engine but install a chip from a reputable company, you can expect, on average an approximate 5 % horsepower increase.

Let's explore the potential modifications to the different functions of the microchip in more detail.

1) An Increase in the Engine Redline or Engine Cut-off.

Integrated into the fuel delivery and ignition functions is the control over the engine "red line", i.e. maximum engine rpm. This is accomplished through a combination of: (1) a reduction in fuel delivery, a soft cut-off, or (2) through the ignition program, a hard cut-off. The redline feature was installed by the factory primarily for the purpose of protecting the engine from overreving. A motor generates its peak horsepower at a point well below the redline. In a non-modified motor any RPM increase, (you usually see about 200 RPM), will produce no additional horsepower.

2) Increased Fuel Supply.

An increase in fuel delivery is also only of value if the engine is modified. Without getting too technical, a motor design is based on a combination of factors including bore, stroke, compression, torque band, and many other criteria. The overall design also includes the determination of the rates of fuel delivery for the engine to perform at its optimum over a wide range of varying conditions. The optimum air to fuel ratio is 14 lbs. of air to each lb. of fuel. Obviously, the challenge is to maintain this ratio consistently throughout the power curve as the volume of airflow increases. The design of the fuel delivery is then verified using the dyno, where the rate of actual fuel flow per minute is measured.

Any significant deviation from the original values can be counter-productive. Less fuel (lean) obviously does not create more horsepower but rather creates, among other problems, more heat. Significantly more fuel does not create more horsepower either. An increased fuel supply can cause a poor idle condition or insufficient combustion. The secret to modifying the fuel supply is to provide the correct amount of fuel at the correct time. Unless there has been a change to the engine design, i.e. increased displacement etc.; the factory has optimized the fuel delivery. Where then is the claimed horsepower increase?

3) Ignition Timing.

Once more, without getting too technical, common knowledge dictates that advancing the timing can create horsepower. Advancing the timing, advances the spark which "advances" combustion. It's here that some subtle increase in horsepower may be found. Again, the emphasis is on subtle. Obviously, when the factory designs an engine, it will compromise somewhat on the timing advance simply because it has no control over the quality of gasoline the Porsche owner has available to him. The higher the octane rating is, the more advanced the timing can be, therefore producing more horsepower. The common misconception is that "more is better." Frankly, the timing can only be advanced so far before detonation sets in (commonly called pinging). In a detonation condition the power loss is dramatic, and can result in serious damage to your motor. Pinging may not always be noticeable, however; you may hear it driving on a steep grade while the engine is under load.

Beginning with the 1989 C4 engine, the factory incorporated the Anti-Knock System into the DME. This enabled the factory to better fine tune the engine because if pinging does occur, the knock sensor and DME will retard the timing. Theoretically, one would think then that it should be irrelevant if the timing were advanced too much. WRONG. If the timing is advanced too far, the two systems will constantly be in conflict, the chip will be instructing the timing to advance and the Anti-Knock will be attempting to retard the timing, resulting in engine performance degradation.

That brings us back to the original question about the microchip performance increases. As discussed, microchip changes can produce some marginal gains. ANDIAL believes that to gain any significant benefit, a properly programmed E-PROM should be combined with additional changes to improve the engine breathing capabilities such as polishing intake plenums, and installing a sport muffler. A package of this nature can produce an increase of as much as 20 horsepower on a 3.2 liter 911 Carrera, to cite an example.

DO NOT fall for a claim of a 30% increase on the rear wheels! Be aware also that chips, especially the early designs, are relatively easy to remove and modify. The program mapping included on a chip is extremely complex and if the programing changes fail to integrate the complete functionality you can easily end up with a performance loss.

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