Chip - Tuning.

[Ascari32]

Still trying to find a solution to what I have long felt an outstanding problem regarding my 3.2 JTS engine. The Colombo Bariani camshafts generate considerable cross - flow and consequently the MAF output voltage is considerably altered from the standard 3.2 JTS.

I believe the Alfa element has an acute dv/df characteristic, to compensate for the inertia NVO. occurring between 9deg.ATDC and 11.5deg. ATDC. It would therefore; in my view, need a sharp response to compensate for the fact that air flow has been stymied for 2.5deg.(static timing).

So, after much research, I bought a MAF element for a 3.8/4.0L Porsche 911 Turbo. This element has a much higher maximum flow rate but its Transfer Characteristic is much less acute: I reasoned, the air flow velocity in the inlet tract of my engine is now much faster and would be better suited to a characteristic that was more "Gently Progressive", with a hight air flow range.

Accepting that it would simply not be a plug and play device, I set about trying to adjust the Porsche element output signal, with limited success. This was done by fitting various resistive networks/attenuators into the output to the ECU [MAF Pin 5].

As I say, success was limited, which led me to research chip - tuning with turbo cars. To my surprise, I came across a device, made for the 3.2 JTS, by the name of "Petrol Chip". So, after some initial questions to the manufacturer, I decided I would try one.

I could not know how it was possible - until I got my hands on the device. Key to it working as well as it does with my engine is the increased air flow through the inlet tract, courtesy of the Colombo Bariani camshafts. From this it follow that output voltage of the MAF is higher, therefor providing extra level adjustment.

It is pleasing to find that although my attempts were crude, they were in the right area. The petrol - chip essentially adjusts the output voltage, whilst maintaining the pivot point of the Transfer Characteristic, something my modifications did not do. It also can be adjusted for 288 Vernier increments in attenuation: 2x12 coarse + 12 Vernier settings, the Vernier's functioning between each coarse step.

However, it does it in a way which is a bit different to the way I was trying and it would have taken me forever and a day to achieve such flexibility in selecting a new setting.

I am only just at the beginning of testing, but already the benefits are obvious. More to the point, it is normally not that easy to come to conclusions so early on when doing experimental work - although my previous tinkering's have helped. However, it is getting to the point where adjustments can be predicted to have such and such effects upon the engine - very pleasing.

So much so, that I was able to refit the Porsche element. This allowed direct comparison between it and the 3.2 JTS element - the Alfa element producing neck - wrenching acceleration from stand still, but losing pace at higher revs, whilst the Porsche element was less dramatic from stand still, but quieter than the Alfa's. But at 3000rpm and above, the Porsche, with it's much greater air flow range was in every sense of the word "Dramatically" quicker. 

Below is from a post I have just made on the UK forum. Whatever I do wrt my engine modifications, I feel it only fair to share them with fellow owners in Aus. I have a very great affection for my 159 Q4 and in particular the 3.2 JTS engine. Although it is a vain hope, I would like to think this car and the JTS engine will eventually be recognised for what it is - a superb Alfa, as good as anything for the last forty odd years.     

Quote:-

"Altered the Chip Tune to 11.1. After a run out with 10:1, it seems the ECU was learning the new flow characteristics, as switching the A/C in now causes the engine to pick up the load. So I increased the attenuation by 1. It is clear however, acceleration is not as sharp as when the 3.2 JTS correct element is fitted. Which fits in with my view, that it; the JTS element, has a sharp dv/df characteristic, but the maximum flow rate is considerably less than that of the Porsche.

Although slower, by some margin on pulling away, the Porsche element comes into it's own at higher revs. It is also noticeably quieter at tick - over than the JTS MAF, which also fits in with the my theory of less enrichment at the bottom end.

The JTS element gives a genuinely neck - snatching effect when stabbing the throttle from the go, but cannot match the rate acceleration the Porsche generates beyond 3000rpm.

These Colombo Bariani's camshafts are said to produce considerable power lift at high revs, So it seems logical that the Porsche element is better suited and I do not want to run the engine lean at high revs. The difference between it and the Alfa element in that area is quite noticeable. At the very least I need to find the best setting prior to putting the car on a rolling road. So it may be that I have to settle for a less dramatic take - off, for the sake of noise levels and top end enrichment.

Things are continuing to change/evolve, as I do further tests. So I need to write this down in the hope that I don't go continually over old ground. On the whole though, I am pleased with this little Gizmo. It has given me much more control of what I had hoped my first tinkering's would produce.

And it confirmed my suspicions about the unsuitability of the Alfa MAF, other than with an unmodified 3.2 JTS engine."