Before you set off on a journey of tuning the 944 Turbo, you need to understand the limitations of the 944 Turbo components. Some components hold back performance, others may break before a certain performance level has been reached. Knowing this information is key to being able to get the best from your 944 Turbo.
Just to recap, in part one we covered the various engines installed into the 944 Turbo over its many years of production, if you have not read it yet, stop cheating and read it first before reading this article!
You may have heard this before, but to improve the performance of an engine you need to improve its breathing. Improving the breathing of an engine involves making the engine more efficient at how it breaths in air and fuel as well as its efficiency at expelling the burt fuel and air. This can be done in many ways, including removing restrictions from the breathing (in or out) as well as improving the way the air is processed and presented to the engine.
Lets look at some basic areas of the car and how they restrict performance.
The boost signal line to the wastegate (limits to 250 bhp)
The signal pipe and cycling valve, which sends boost pressure to the wastegate to open it, as standard is designed to limit boost to factory levels. With a standard wastegate it can be improved with a boost profiler, but with a dual port wastegate it would need to be replaced with a manual or electronic boost controller.
Engine management chip (limits to 265 bhp and 260 ft-lbs torque)
The standard engine management chip limits power because that is all it was designed to do, provide software and maps for the standard engine to be provided with the correct fuel levels and spark timing required by a standard engine and turbo. The result is that the engine is limited to 265 bhp, which can be performed by using a boost profiler to allow the engine to hold onto boost a little longer and allow it to build a little quicker. A good upgrade, but don't go any further than this without a replacement performance chip or a custom programmed chip.
The catalytic converter (Limits to 275 bhp and 300 ft-lbs torque)
When fitted, the catalytic converter is designed to change the state of exhaust gases from harmful gasses into less harmful gasses and water vapour. However its design hampers performance and strangles the engine. At best, with the catalytic converter installed, I do not recommend the performance is increased beyond 275 bhp or 300 ft-lbs of torque, as it is not only not nice to the catalytic converter (which can melt, causing a blockage and breakdown) but also to your engine, which will see very high combustion temperatures in the engine as well as in the exhaust. With this limiting item installed, you are limited to a boost profiler device or a set of chips at modest boost levels only. Its replacement can be a "Cat bypass" or "Cat delete" section of exhaust, or its replacement with a silencer.
Fuel pressure regulator (Limits to 275 bhp and 350 ft-lbs torque, with standard injectors)
With standard fuel injectors and fuel pressure regulator, the 944 turbo is limited due to the amount of fuel that can flow through the standard injectors at the standard fuel pressure. Upgrading the fuel pressure regulator to a 3.0 bar item (standard is 2.5 bar) can increase the fuel flow of the standard injectors to around 320 bhp and 350 ft-lbs of torque with the correct engine management chip.
The wastegate (Limits to 300 bhp and 300 ft-lbs torque)
The standard 944 turbo wastegate has a couple of issues. One, it opens slowly as boost increases above atmospheric pressure, this means that as soon as you get any boost, the turbo will begin to see less exhaust gasses flowing into it, therefore causing it to not increase boost as quickly as it could. The next issue is that as the RPM's increase on full throttle and full boost, the exhaust pressure in the exhaust before the turbo will rise to such a point that it will be opening the wastegate early, causing a drop off in boost pressure, which therefore also limits power. This can be improved with fitting a boost profiler, but ultimately a dual port wastegate of good design is required to take the car beyond 300 bhp.
Fuel pump (Limits to 320 bhp and 375 ft-lbs torque, when new!)
The standard Porsche 944 Turbo fuel pump delivers more than enough fuel for a standard engine. In fact a new fuel pump will provide enough fuel for 320 bhp. However, as the fuel pump ages, the fuel flow of the pump reduces, so also the amount of horsepower the fuel pump can provide for also reduces. This is particularly dangerous as if the rest of your package can provide more airflow for power, and your fuel pump is under performing, a lean fuel mixture can cause catestrophic detonation of your engine. Not advised. We recommend the install of a motorsport fuel pump, which fill fit in exactly the same way and provide enough fuel for a 550 bhp monster!
Fuel inectors (Limits to 320 bhp with uprated fuel pressure regulator)
At the standard fuel pressure of 2.5 bar, the standard fuel injectors can only flow around 275 bhp worth of fuel, at 3.0 bar with an uprated fuel pressure regulator they are limited to 320 bhp. Upgrading to larger fuel injectors, such as #55's or #72's increases the fuel flow, which then advances the limits of the injectors drastically.
The air filter box (Limits to 320 bhp and 375 ft-lbs torque)
As standard, the 944 Turbo air filter box and snorkel tube, like many other parts, can only flow a certain volume of air per second. We have found in testing that it usually limits the power to 320 bhp and 375 ft-lbs of torque. Replacement with an induction kit, should remove this limitation.
Typically, many people will tell you that the induction kit needs to place the air filter somewhere that it will recieve cold air, however, when the car is moving, often the under bonnet temperatures where an induction kit will place the air filter will not be as high as one would expect. However a better solution is always to have cool air feeding the air filter.
Replacement of the air filter box with an induction kit will also reduce the amount of time it takes the engine to create boost, making it less laggy.
Turbo Charger - K26.6 (Limits to 290 bhp and 375 ft-lbs torque)
The baby turbo fitted to the 944 turbo from 1985 to 1989 as standard (except Turbo S models) is very good at spooling up quickly and producing boost early, but this very design feature also means it runs out of steam by the time it is flowing enough air to produce 290 bhp. However its ability to spool up quickly means that it can provide quite a lot of torque. Remember, a turbo charger, like an exhaust system limits power due to its ability to move a certain volume of air per second. The lower the engine speed, the more time per second the engine is able to breath, so a small turbo like this can provide a lot of low down power due to its ability to create boost at lower rpms.. But that also means that at higher rpms, the turbo may not be able to keep up, beyond a certain level, the turbo will become inefficient and will generate more heat rather than more airflow beyond a pre set level of load or power. This limit can be removed of course with a bigger turbo, typically though, that also means more lag.
Turbo Charger - K26.8 (Limits to 320 bhp and 365 ft-lb of torque)
This turbo, fitted to the 1988 944 Turbo S and all 944 turbo's after 1989, is able to flow 30 bhp worth of air more, than its little brother the k26.6. Unfortunately it is at the expense of throttle response and increases lag. It was fitted because it allowed the Turbo S and late 944 turbos to produce a higher peak bhp, this often means that a standard 220 turbo is quicker out of the corner (less lag and more torque), but the Turbo S (or 89 on) car is quicker in higher gears. The limitation, like its little brother the K26.6 is due to it moving out of its efficiency band at around 320 bhp worth of air, beyond this it creats heat rather than more power, which can cause detonation of your engine.
Intercooler (Limits to 320 bhp and 375 ft-lb torque)
The standard intercooler design has poor flowing end tanks. There is much debate if this was a designed in feature to stop tuning, or if it was to help distribute flow across the entire intercooler at normal boost and airflow levels. But beyond 320 bhp worth of air, the standard intercooler is unable to flow as much air as the matrix within the intercooler can flow. An intercooler with modified end tanks is required to flow air beyond 320 bhp.
The air flow meter (AFM) also known as a VAF Meter (Volumetric Air Flow Meter). (Limits to 340 bhp and 400 ft-lbs torque)
The standard airflow meter as standard works fine, however it only measures airflow at low and mid range levels of rpm and boost, or to be more accurate "load", as such, when on a full throttle, full boost run, the engine management system is assuming a certain level of boost is being reached at a certain rpm at full throttle, not good for a very high performance car, so it is advised that you upgrade to a MAF sensor before you reach this limit or level. However, it has another limiting factor, which is that it can only flow a certain amount of air, which unfortunately hinders performance gains and limits them to around 340 bhp and 400 ft-lbs of torque. Beyond this, another air measurement device such as a MAF sensor or MAP sensor is required.
The exhaust system (Limits to 350 bhp and 400 ft-lbs torque)
The exhaust system fitted to the 944 turbo typically limits performance to 350 bhp and 400 ft-lbs of torque, this is because the volumes of air (or exhaust gas) required to produce more than this power level are more per second than the standard 944 turbo exhaust system can flow. Try to go beyond this power level with a standard exhaust will result in very little performance gain and increased temperatures within the combustion chamber. The standard system has a diameter of 2.5 inches, where as increasing its diameter, all the way back to the turbo, can remove this restriction. 3 inches is really the sensible upgrade diameter.
The standard engine - M44.50, M44.51 and M44.52 (420 BHP and 420 ft-lbs torque)
The standard 944 turbo engine, no matter what version it is, usually is fine producing 420 bhp and 420 ft-lbs of torque without issues, even if it has many miles on the engine. Obviously, if there is a component within the engine which has not many miles left on its service life, then upgrading the power in the engine is likely to reduce its lifespan. I often tell customers who are interested in tuning their 944 turbo that if their head gasket has not been changed in years and it maybe has another year or two left before it blows, then it may blow much earlier, or even right away if the performance is increased. We have taken standard used 944 turbo 2.5 engines beyond this level of tune, but to be honest, its a worry if the con rods, pistons or other components will survive. Certainly I would say that under 350 bhp a standard engine should have no issues, and ideally if tuning to 420 bhp I would recommend using a M44.50 engine with its superior strong block and pistons, but not essentially.
Every part above can be replaced with a less limited or unlimted item and at JMG we can provide any part you need for tuning your Porsche 944 Turbo, the sky really is the limit, we have even built 3.2 Litre engines for customers which are capable of 700 ft-lbs of torque as well as 2.8 and 3.0 litre turbo engines, every package is different, just as every customer and what they want to achieve is different, so for every package of different parts may provide a different output performance. All of the above information is based on experience and scientific experimentation, however every customer package is dependent on many factors and we can only estimate the final power delivery you may enjoy.
In the next installments we will look at what performance gains can be had from different performance products. But also look out for some of our other technical articles where we will deal with many other aspects of modification and performance tuning.