PROFESSIONAL MOTORSPORT
SIMULATION SOFTWARE
Comparison with calibration data for development stages
The standard ECU was replaced with an Bosch Motorsport MS4 ECU running the Clubsport Software, developed by the much appreciated Jochen Hertkorn. We are a big fan of the clubsport software he developed and very much regret that he choose to leave Bosch Motorsport.
In addition to the MS4 ECU, a C40 logging device was mounted, so the data of all the drives could be logged and later analysed.
Calibrating the engine of a car which one drives on an almost daily basis is the ultimate experience for an application engineer. It generates a completely different feel for the calibration.
Bore x Stroke:
Compression ratio:
Mechanical Losses:
100 x 76.4 [mm] (6 Cylinder)
11.3 : 1
1.9 [Bar]
Intake Valves:
Exhaust Valves:
1 x 49 [mm]
1 x 42.5 [mm]
Inlet Camshaft :
Exhaust Camshaft :
240 [mm] (@ 1 [mm] lift)
228 [mm] (@ 1 [mm] lift)
Intake runner:
Primary exhaust:
300 x 42 [mm]
350 x 39 [mm]
Original engine run on Bosch MS4.0, with catalytic converter
Out of the calibration, the fill rate of the engine can be derived, because that is equal to the injection timing multiplied with the lambda. Much attention has been giving to ignition in combination with the knock detection and control.
Due to the aircooling, the spectrum in which the engine operates is large. it gives the opportunity to analyse the influence of engine temperature on the fill rate, knock and ignition timing. In order to analyse the influence of injection timing, the injectors have been replaced by the 993 Turbo injectors.
Since the car data are known, acceleration tests could be performed which can directly be compared with the simulation. This gives the opportunity to determine the power and torque curve of the engine, without using a test bench.
Delete of the catalytic converter
The first major change, was the delete of the catalytic converter. The converter generates a lot of back pressure to the engine.
By deleting the catalytic converter, the exhaust gas temperature decreased significantly, which is an indication of the amount of backpressure the converter generates. Less backpressure enabled more timing advance. In addition the reduction of the backpressure caused a slight increase of the fill rate of the engine.
As can be seen in the results, it caused a significant increase in power and torque. The higher the rpm, the bigger the improvement.
It is often said that the 993 exhaust is a big improvement over the 964 one. From our point of view, that is only true if both are run with catalytic converters. The 993 has two catalytic converters, each of them much bigger than the single 964 unit. So it is only logical that the backpressure of the 993 unit is a lot less.
LapSim designed camshaft for 964
The second major change to the 964 engine was replacing the standard camshafts, by custom made camshafts. Because the car is used on the normal roads, we wanted to improve the drivability of the engine, not just increase top end power.
Out of the simulations, we assumed that most replacement camshafts focus more on top end power at the expense of a wider powerband. As can be seen in the resulting power/torque graph, the custom camshaft delivered significantly more power, but even more important also a significantly increased power band.
We were quite surprised about the improvement of the engine, due to just a camshaft change. The 3.6 got more torque than most 3.8's and significantly more power than them. We wondered why Porsche have overlooked such a simple change?
Looking back in the details of the Porsches of the 70's and 80's, Porsche was using the 964 camshaft profile already for a very long time (15 years??). They merely only changed the lob centre position. It makes one wonder why this special Porsche 'profile' was not touched for so long.
Equal length exhaust headers with 750 x 42 primary tubes
The third change was the replacement of the standard exhaust to a equal length exhaust system, including heaters.
From a performance point of view it certainly delivered. More torque, more power and a wider powerband. However it had a bad resonance at about 2000 [rpm].
So we decided to shift back to the original exhaust system, although we severely missed the extra performance. If you are going to use your Porsche mainly on the track, we would advise to replace the standard exhaust system. For normal road use, we like the standard exhaust. Without the catalytic converter, it is not that bad and we love the sound.
VarioRam intake: till 5100 [rpm] 525 [mm] intake runners
The extra drivability of the replacement exhaust, raised our interest in an option Porsche introduced on the latest aircooled engine, the VarioRam system.
With the VarioRam, the engine characteristic transformed from a peaky flat 6 to a big capacity V8. At 3000 rpm, you already have 300 Nm at your disposal. Peak torque is at 4400 rpm.
With this engine, the standard 964 gearbox became way to short. We decided to change the gearbox for a much longer 965 unit. The combination worked perfect.
The 'long' 965 gearbox together with extremely wide powerband, made it a very economical car. Fuel consumption decreased by about 20%. Furthermore, due to the strongly reduced rpm, noise level on the highways was a lot lower, making it a very comfortable car.
The only 'negative' aspect of the VarioRam, was that the camshaft could have been more focussed on top end power, because the VarioRam sorts out the torque at low rpm. Unless you are going for maximum performance, you tend to shift @ 5000 rpm, even when driving fast.
Many tuners do not like the VarioRam system. We completely disagree. We love it. We would always use it, if we had the choice. For a pure racecar, one could argue that the benefits are small, because you mainly drive in the higher rpm. But still, coming out of corners, we think it more than compensate for its extra weight.
LapSim designed camshaft for 993 VarioRam
So when an original VarioRam engine became available out of a crashed car, we decided to use that as a base for the 'ultimate' engine for the street 964. The second generation 993 engine has larger intake and exhaust valves.
Out of our experience with the VarioRam, a 2nd custom made camshafts where developed and made, which focussed more on top end power, because VarioRam would take care of the drivability.
It has hydraulic lifters, which we kept. We wanted to try how well they worked, before changing them for solid lifters, which seems to be the common advice. The hydraulic lifters work absolutely fine. We expected them to reduce the fill rate at very low rpm, but that does not appear in reality. A first generation 993 engine feels weaker at low rpm than a 964 engine. We believe that is due to the exhaust system of the 993, not so much caused by the hydraulic lifters.
As you can see in the resulting power torque graph, the performance of the engine was raised over the complete power band, but with more focus on the higher rpm. This engine starts pulling from 3000 and just continues to do so till the rev limiter at 6750 rpm. In combination with the 965 gearbox, it is a dream to drive and seriously quick.
In reality it has about 325 Hp. That may not sound so much in this day and age. But in a small 964 C2 body, it almost reaches the rev limiter in 5th gear of the 965 gearbox, meaning it is not far from a real 300 km/h.