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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.
The different Porsche 944 Turbo engines and the cars they were installed in.
Tuning the Porsche 944 Turbo is something that we at JMG Porsche have been doing extensively for many years. We redesigned the standard 2.5 Litre engine in 2005 to provide the worlds first 3.2 944 Turbo engines as well as building the very best 2.5, 2.8 and 3.0 engines for 944 Turbos. We have even tuned standard engines with over 100,000 miles on the clock to have over 400 horsepower reliably. So you could say we know what we are talking about.
In this series of articles, I plan on showing you what can be done with a 944 Turbo to improve its performance, you will learn what the limits are to the original components and what can be done to improve those components.
So first things first, we need to cover the basic engines installed into the 944 Turbo and the turbo chargers the factory connected to them.
Porsche officially launched three revisions of 944 Turbo engine. The M44.50, the M44.51 and the M44.52.
In 1985 when Porsche released the 944 Turbo, the original engine was an M44.50. With a capacity of 2.5 Litres, this engine was designed to be the test bed that the first customers of the 944 Turbo would be unwittingly testing for Porsche along with long term Porsche test cars, some fitted with a M44.50 engine as fitted to the production cars, others fitted with a M44.51 and some fitted with a M44.52. As Porsche were a low volume car manufacturer, this allowed Porsche to trim the production costs of the engines over time, as their test cars mileages rose higher without issues and the customers cars were monitored.
- This original version of the engine, the M44.50 featured the following:-
- Sodium filled exhaust valves
- Ceramic coated exhaust ports
- Modified engine block
- Thicker engine casting with higher density aluminium engine block
- Forged piston connecting rods
- Manual Cam belt tensioner
- K26/6 Turbo (Size 26 compressor matched with a size 6 exhaust turbine.)
This engine produced 220 bhp @ 6000 rpm and 243 ft-lb @ 3500 rpm, and was almost completely bullet proof. If anything Porsche knew it was capable of much higher performance, but due to the superior weight distribution of the 944 design, more performance would have made it faster than the companies flagship 911 Turbo on the road or track. Arguabley the 944 Turbo is faster on the bends and is certainly no slouch on the straights, so it was decided to limit power to 220 bhp.
Half way through 1986 the 944 turbo received the M44.51 engine which had now seen another year of testing in the factory road test cars, so it was put into production as the new engine for the 944 turbo. Much the same as the M44.50, but with the following differences.
- Thickness and density of the engine block reduced back to the same as a 944 non turbo to reduce production costs
- Cast piston con rods instead of the expensive forged con rods of the M44.50
For normal or tuning use, there is no difference between the M44.51 and the earlier M44.50 except these components were downgraded in the later 51 engine. However, for the engine builder wanting the best from factory components, a M44.50 block and M44.50 con rods are sought after.
The M44.51 engine still featured the same K26/6 turbocharger and provided the same power output of 220 bhp and 243 ft-lb torque.
During 1987, Porsche had finished testing with a new upgrade for the engine, an automatic cam belt tensioner, wider balance shaft belt (most earlier engines were upgraded during service belt replacements) and a deflector rail on the waterpump. Other than this, the engines are identical. This version of the engine continued until the Porsche 944 Turbo stopped production at the end of 1991 and the begining of 1992.
It is said that the M44.52 engine is one that produces 250 bhp, this is not true, but we will cover that in a moment.
The early cars before 1987 featured a different wheel offset to the later ones, something that changed with all Porsche models in that year, this was done to improve handling and road safety, although it is also said that these earlier cars are more edgy and track focused, partly due to the lack of option for anti lock brakes (ABS) and a limited slip differential, but also due to the geometry caused by the wheel offset, but thats for another article.
After 1987 the engine changed to the M44.51 engine, performance was unchanged, the wheels changed to the later offset and some extra options became available such as ABS.
In 1988 Porsche had been racing a more powerful and upgraded 944, the 944 Turbo cup for a little while and decided to make a special edition 944 Turbo, the 944 Turbo S. This featured the sports MO30 Suspension and brakes, a larger turbocharger, the K26/8 (Larger exhaust turbine and housing) and a limited slip differential (LSD) all lifted directly from the 944 Turbo Cup race cars. The Turbo S featured 250 bhp @ 6000 rpm and 258 ft-lb of torque, an impressive increase in power, but with slightly more lag than the 220 bhp versions with the smaller turbo. These cars were fitted with the same M44.51 engines that all 944 Turbos had for the previous year and the non turbo S cars of 1988.
The turbo S version of the car was sold as a limited edition, at a price premium. Much to the annoyance of Turbo S owners, the following year in 1989 Porsche upgraded the standard Porsche 944 Turbo so that all 944 Turbo's featured the same K26/8 Turbocharger, and so produced the same power output as a Turbo S. Although in most international markets, the MO30 suspension, brakes and LSD transmissions were still optional.
Over the years there also were many changes to the 944 Turbo other than what we have mentioned here, but we will cover those in other articles as time goes on. For the moment, we have been interested in the engines, the years and what changed, as well as getting rid of some myths at the same time.
By now, you should have a good understanding of the 944 Turbo and its history, as well as the engine and the differences in the engine types.
In the next installment we will look at the Porsche 944 Turbo, component by component, to assess the tuning limitations of each part...