[MNBoxster]

Originally Posted by Bavarian Motorist

It's day 3/12 (12 because I want to allow a day to send it back if necessary) now, Jim. I will be reporting every day to see if I can get you guys the most info I can.


I have heard all of the things you say so many times. That a tune by itself will not yield much benefit..that you need to remove air restrictions...that my type of engine can't be improved that much.


That's why I am so surprised myself!




Well, I asked them what exactly they DO. They told me, and I'm not sure if this is what all ecu tuners do, but bear w/ me... that the majority of what they do is just making sure the fuel injection and spark plug ignition take place as close together in time as possible...might improve MPG? Certainly is more fuel efficient.



Do you think the dramatic temperature change made a substantial difference? Like I said, the majority of the time I've had my car it's been in the 30s and 40s...and then the day I get the ECU back, it's 65 and I am not impressed w/ the results. The very next day, it's 40 out and I am suddenly impressed.



Let it be known that I want this to be real. I don't just want to think it's real or pretend it's real. So let's hope

Hi,

I think you're trying to convince yourself. What they told you they do to the Fuel Timing Maps is a very broad statement - all Maps involve syncronizing the Injector Pulse Width with the ignition (spark), but so far as taking place as close together as possible, this isn't true. And how they do what they do is just as important as the end result. Do they produce new Maps? Or (most Likely) do they introduce software to fool the DME into selecting different Maps than it otherwise would for a given set of operating parameters?

The Fuel Timing (when the Injector is pulsed) is dependent upon the engine's Duty Cycle. That is, when the Intake Valve is closed and the Piston is on it's Compression Stroke. This allows the Fuel and Air to emulsify (mix) and compress to achieve the best combustion. The length of this Injector Pulse (called the Pulse Width or Duration) determines how much Fuel is introduced into the cylinder.

Now the time interval of this Duty Cycle changes in response to how fast the engine is turning (RPMs). The Compression Stroke on an engine revving at 6k RPM is half as long in duration than one for the same engine revving at 3k RPM and the Injector Pulses (not the Pulse Width, or Duration) are twice as far apart for the 3k RPM mode than the 6k RPM one.

As far as Spark is concerned, the Duty Cycle is also important, but for different reasons. The Ignition of the Fuel/Air Mix starts at the Spark and travels (or propagates) outward to the Cylinder Walls. This takes Time (although it is measured in nanoseconds, it still takes Time nonetheless). In order to capture the maximum energy the A/F Mix contains, all the mix must be combusted just as the Piston reaches it's uppermost position - Top Dead Center (TDC). This makes the most energy available to push the Piston back down. If this doesn't occur, either some fuel is left unburned or the energy from that fuel isn't available to do Work (push the Piston). So, the Spark must occur at a precise optimal point in the Duty Cycle. But, since the Duty Cycle duration is variable (depending upon engine RPMs), this optimal point for the Spark to occur also changes. In the 6k vs 3k RPM scenario, in order for the A/F mix to properly combust, the Spark must be introduced sooner at 6k RPMs than at 3k RPMs, this is known as being Advanced (or sooner before TDC is reached).

These Optimal Points for Fuel Timing and Spark differ throughout both the RPM and Load Range and are independent of each other. This means you don't always want them as close together as possible, contrary to what you've been told. They have been determined experimentally in the Lab and are programmed as code into the ECU (DME in Porsche Parlance) and are called Maps. Using the signals from various sensors in the engine and car, the DME compares actual conditions to a set of known conditions and selects the correct Map programmed for those conditions and energizes the Fuel Injector and Spark Plug accordingly.

This is the very basic function of the DME. But, the Maps also incorporate other considerations such as Intake Valve cooling, Detonation Thresholds, Emissions, MPG (Lean Fuel Metering - Cruising), Fuel Quality, Engine Service Life, etc. which may set the Fuel and Spark introduction at other than Optimal Points (less than Optimal specifically for Performance that is).

A typical re-chip does not find some new Magical points at which to fire the Injectors or Plugs, it most often uses software to mask or alter the signals the DME receives from it's various sensors to fool it (the DME) into ignoring many of the non-performance related parameters and adjusts the firing points accordingly by selecting different Maps than those called for by the actual operating conditions. This will increase Performance, only very mildly for an NA engine - greater gains are to be had on Forced engines (such as Open Exhaust Valve combustion to maintain Turbo RPMs, etc.).

But these re-chips are dependent upon the DME's Memory Capacity. The file size for Bosch Motronic 5.2 (2.5L engines) is 16 Kb, 512Kb (or 32X more) for Motronic 7.2.2 and 720Kb for Motronic 7.8. This means that there is more to work with on the ver. 7.8 than the ver. 5.2.

Temperature has little to do with it as it is already compensated for in Air Mass determination and Engine Temp. - the DME adjusts accordingly.

Also, just as important as achieving a gain, you have to look at where those gains take place in the Power bands. If they're all at 6k RPM and above, you're rarely gonna tap into them anyway. The greatest gains to be had from a usability standpoint are in the mid-ranges and most of what you report is at the extreme.

The amount of gain really depends upon how poorly the original Software was written. These Gains are not Made, rather they are found within defficiencies of the original software.

One has to assume that Bosch/Porsche did a pretty poor job, leaving a lot on the Table, in the initial programming to assume that a re-chip can produce substantial gains.

I'm not willing to make that assumption, especially since the engine, in stock form, has such a high Horsepower/Displacement ratio as compared to many, many other Performance cars, including the famed 550 Spyder.

You may find trading $600 for a couple HP and/or Ft.lbs. of Torque (at best, if at all) as a good trade, I do not. And, I think there are many here who feel the same way. I mean that's 3/4 the cost of a new set of tires, or shocks, and such and I think most people with limited funds to spend on a fun car have to look at it this way.

Anything less than a 15HP gain leaves the car essentially as it began. You can say you have 3 more HP, Hooray for you! But that doesn't mean squat in the real world...

Happy Motoring!... Jim'99