Please note that the answers to questions in this section are purely the opinion of ANDIAL. Statements made in this section are not of the high-tech nature, but they are merely an attempt to explain some of the basics or certain performance aspects to the Porsche owner. The components discuss in this section tend to be the ones that lend themselves to certain modifications and consequently, there exists a tendency to create overrated expectations.
Question #1
I want more power and I’ve seen ads that promise 400, 500 and 600+ horsepower. I am a member of a Porsche club and intend to take my car on the track for some club events therefore I want the most power available i.e. 600+ horsepower. I intend to use the car 80% on the street and 20% on the track. Can you build me an engine?
Performance and horsepower. This is probably the most misunderstood and misrepresented measurement of performance that exists. Logic would seem to dictate that if power equals performance, and horsepower equals power, then horsepower equals performance. WRONG! Horsepower by itself does not necessarily translate to performance.
Making horsepower, especially with turbocharging, has never really been an issue. The 1975, 935 generated 590 HP at 7,900 rpm out of 2.9 Liter displacement. This was twenty years ago!
Could a car like this be driven on the street? Not a chance, this engine had a power band of probably 1,500 rpm and would generate very little horsepower below 4,000 rpm.
Remember, an engines power curve is not linear; 450 HP at 6,000 rpm does not translate to 225 HP AT 3,000.
It seems obvious that a street application using a race motor would be totally inappropriate, however; this is essentially what many "engine tuners" are selling. They build a motor, mount on a huge turbocharger (see question #3), crank up the boost, run it on 104 octane race gas and yes, you can achieve a flash dyno reading of 500 HP at 6,500 rpm. This should be your first clue. When you hear a statement of this nature...RUN!
What needs to come into play here is some common sense. Think about it, the 1998 Porsche Factory 911 GT2 race car, with 3.6 Liter displacement, twin turbochargers, and twenty-five years of racing research and development with turbocharging behind it, generates 485 bhp. Could it be that the factory should have had their cars built by some of the aftermarket tuners? You would think they could save millions in research and development.
The reason the factory invests the amount they do is simple...they need to win races. And to win races, you need to be able to perform, and you need to finish! The factory is after the same thing that you are; consistent reliable performance. The factory understands the relationship between performance and horsepower. Horsepower by itself is not the relevant measure.
The Porsche owner needs to know the right questions to ask. Don’t ask about horsepower ratings; ask what modifications will provide the performance to match your requirements. Define what you hope to accomplish!
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:
1. To control the fuel delivery through fuel mapping.
2. 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.
Question #3
I am looking for more performance for my turbo. Will a really big turbocharger give me more horsepower?
A larger turbocharger will not normally create more ultimate horsepower. What the different turbochargers do is change the rate at which the boost is created, therefore they change the engine’s power curve. The larger the turbo, the more turbo lag, but the less horsepower drop-off at high engine RPM. On the other hand...The smaller the turbo, the less turbo lag, but the higher the horsepower drop-off at high RPM.
The basic principle of turbocharging is that the turbocharger creates the boost, which results in a compressed fuel mixture. Once the maximum pressure the engine can take is reached, any excess pressure is released through the wastegate. The wastegate is a valve body that is preset by a spring, which opens when boost pressure exceeds the spring tension. This prevents damage to the engine from an excess boost condition. However, this same function means a turbocharger’s ability to generate higher boost levels is irrelevant as any excess boost is vented from the system.
Horsepower in itself is not generated by the turbocharger. Examples of extremely high horsepower rated turbo race engines, i.e. 1,100 hp in the 917/30 are a function of the engines ability to handle a higher than "standard" boost level, which in turn is a function of the overall engine design, quality of components, and quality of assembly.
Let’s discuss the mechanics of turbocharging. There are two ways to get "charged" air into the combustion chamber. Turbocharging and supercharging. As compared to the normally aspirated engine where the pistons are required to suck in the fuel mixture through the intake stroke, the "charged" motor has this mixture forced into the cylinder by the turbocharger or the supercharger.
Both methods share the common goal of supplying a compressed fuel mixture into the combustion chamber. The denser mixture results in stronger combustion and a more powerful stroke. The turbocharger versus the supercharger has one distinct difference: While both the turbocharger and the supercharger have a turbine wheel that compresses the intake air (cold side), the supercharger has a pulley attached and, by means of a belt, the turbine wheel is driven off the crankshaft. The turbocharger, rather than a pulley, has an additional turbine wheel (hot side) that is set into motion by the exhaust gases before the exhaust gases exit through the muffler. The obvious goal is to have the right amount of boost available at all times to produce the maximum horsepower.
Why the different size turbochargers? Porsche uses a variety of turbo chargers including the K24, K26, K27, K29, K31, and once there was a K36 (934 Turbo GT.) These numbers may look familiar to you. You've probably seen them advertised as "bolt-on" improvements. The numbers refer to the actual sizes of the fan wheels. A description of the different combinations and there effect is as follows:
A) Small (HOT) + Small (COLD) fan wheels = a quick response but no top-end.
B) Small (HOT) + Large (COLD) fan wheels = medium response with better top-end.
C) Large (HOT) + Large (COLD) fan wheels = marginal low-end response with good top end.
The smaller the fan wheel, the more instantaneously the necessary RPM can be obtained to make the maximum boost. In other words, an ideal situation would be a small hot wheel and a large cold wheel. Exhaust gases propel the small hot-wheel. Exhaust gases are a force greatly dependent on the engines RPM, hence the nature of the compromise. At a lower RPM, the smaller hot wheel cannot drive the larger cold wheel to create boost until a certain engine RPM is reached. This creates turbo-lag. Turbo lag is the interval between the initiation of acceleration and the employment of power. In extreme cases you would have no power below 4,000 rpm and the next instant when the boost comes on full. Since the objective is to have usable horsepower, not only at peak rpm, but also at midrange and lower rpm, compromises in the size of both fan wheels are necessary. In a competition motor, the issue of low-end boost is of lesser importance because racing engines rely on a very limited high RPM range in order to create maximum horsepower.
One might be led to believe that bigger is indeed better but don’t be mislead...its not that simple. There are physical laws to be obeyed and compromises must be made. Depending on the design of the engine, one thing is certain: There is only so much boost an engine can absorb. Obviously, the quality of components such as pistons, cylinders, connecting rods, etc. is crucial. Other determining factors include compression ratio, internal cooling capability, and the ability to dissipate heat from the cylinder head area. Turbocharging creates horsepower, but it also creates tremendous pressure and heat. This pressure and heat are what can destroy your motor and under extreme boost conditions, and this can take place in seconds. Obviously, a competition motor has far superior cooling capabilities, both air and oil, than the average street turbos. A street turbo generally runs safely at approximately 0.7-0.8 bar boost (1 Bar = 14lbs.). A competition car typically will run at 1.4-1.6 bar boost for short periods. The difference in boost levels is what creates the horsepower.
With the 993 B-Turbo, the over boost regulation is done using a wastegate which is controlled by the DME control box. To increase the boost rate in a B-Turbo therefore, reprogramming of the DME unit is required. The 993 B-Turbo S-version, with 430 hp vs. 408hp, is a case in point.
An ideal solution would be to have two (twin) Turbos of a small to medium size. Porsche demonstrated this feature on the 1986 959 model by putting two (twin) turbos in sequence, minimizing turbo-lag. Unfortunately, to do it right was very costly, and it was decided not to incorporate this feature into production models.
Beginning with the 993 B-Turbo, two medium sized Turbos are used. Additionally, engine size was increased, compression was raised, and a more effective ignition and fuel injection was incorporated. This, combined with the ratios available in a 6-speed gearbox, virtually eliminated the turbo-lag.
There are, of course, many enhancements that can contribute to improvements in turbocharging performance. These include sport intercoolers with greater cooling capacity, fuel enrichment systems, and improvements to the flow rate of the turbocharger housings.
The bottom line is this: bigger in not necessarily better for your street turbo! Yes, there are turbochargers that are an improvement over stock, but bolting a K-31 on your otherwise stock-motor will do nothing for the driveability of your car despite the fact that it may add some horsepower to the top-end of your rpm range. To achieve this top-end you will compromise power in the low to mid-range power band and on the street this is where you need it. When was the last time you wished you have more kick at 140 mph?
A common misconception is, "If I get flash reading of 600 peak horsepower on the dyno, some of it has to trickle down to my lower RPM range." It will not! We are not saying that you can’t build a car that has extreme horsepower. We are saying these cars are not intended for street use. If you have driven a car with over 400 "street" useable horsepower, you have an appreciation of how fast and how deadly the potential.
One of ANDIAL’s projects was a street car with a motor capable of producing 700+ hp. This car was a Carrera 4 with a water cooled, twin turbo-charged 962 engine and this engine had to be de-tuned down to 520 hp so the car could be controlled and to ensure longevity of the power-train. Read about the car in our Projects of Interest Section.
ANDIAL gained its knowledge of turbocharging through the development of the racing motors tested on the toughest tracks in America, by some of the world’s greatest drivers. We have been involved since 1976, beginning with the early 934’s and 935’s. ANDIAL’s credentials include 917’s, 962’s and the Can-am 917/30, which generated 1,100 hp.
Throughout this broad range of cars, the objective remains the same: Develop the power to match the application, and balance the dynamics of the car so that it performs to its capabilities. The game hasn’t changed. The same rules of physic continue to apply.
