Road dyno my 996 - help with input variables needed

I have since some weeks a piggy back ECU plugged in onto the ECU and I can now adjust timing and injection for the engine myself. Advantage is that the internal safeguards for the engine inside the ECU remain intact and functional so no big danger of doing something wrong. Started with small delta-adjustments to the current mapping and try evaluate them with my butt-dyno, insofar my butt is sensitive enough The piggy-ECU has an optional road dyno function. Not that the absolute values are of any importance but it will allow me to compare the performance of different delta-mappings and see which works best for me. To get a more or less usable result I need some car parameters which I feed to the software. Some numbers I could find. Others I am not sure if they are what is described. Anybody can check or give me a lead? Here under is a screenshot of the data needed. Coefficient of drag for the 996.2 = 0.30 maybe 0.301 with spoiler up (Adrian Streather's Essential companion) Frontal area = 1,903 m2 (for 996 C2 narrow body: Essential Companion) Gear ratio: in the manual it is describes as the difference in rotational speed from the input to the output shaft. So for a dyno run in third gear it would be 1.52? Driving axle gear ratio: do they mean final drive? then it is 3.44 Tire section width: in my case 295 Tire profile: 30 Wheel diameter: 18 Any comments in what range trans and tyre losses would be? I know for comparing between results in a relative sense it will not be so important. As I would be running the same setup and the runs will be done in as best possible identical circumstances. But it would be nice to come to a best estimate and why not to come as close as it gets to an acceptable absolute value. Some googling gets me numbers of 12% transmission loss for a 996 C2. So 17-19% total losses would be an accurate total estimation. As to the rpm correlation of the losses I am for too inexperienced with the subject-matter. Maybe some of you experts could chime in!

Silk - Have you reached out to people who have dynos? Seems they would know every parameter used.

Very interesting project... what are you using to piggy back the factory system? PS if you are on FB, DEEJAY MARKSKI is a local to me Porsche Turbo tuner and fabricator. He has a LOT of tuning experience on Porsches. He might be a good resource for the info you are looking for.

Scroll down to step 3 of the following: https://www.6speedonline.com/forums/...ta-thread.html

https://www.ecumaster.com/products/digital-ecu-tuner-3/ fairly simple install I have a switch near the door sill to switch between two different maps. acces is very easy via a usb connection and their software I am able to shift ignition almost 8-9 degrees earlier without any problems. For the an atmospheric engine the delta mapping is fairly easy. A single column for rpm - timing and rpm - injection The device has a map sensor so you could additionally run a line to the intake to measure the vacuum there and make a more extended mapping based on rpm and intake vacuum (amount of throttle). You could even go further and log with the map sensor the complete working range of your maf sensor. After that you could bypass the maf and run if based on the map input. This is much more reliable as the maf is influenced by heat soak, ageing etc. Even going further it has an output which makes you able to use water or ethanol injection. Plenty of exotic things. But most interesting is the map tuning. No magic! Gains are lowish and in line what can be expected compared to those of the respectable tuners. Nice thing is you can easily fine tune it yourself for your specific engine. Other cars with same piggy back have shown an 25-30Nm increase in torque, not at peak torque but in lower to mid rev range. Definitely makes the car quicker. Just curious how good I can finetune it myself. My car has some small mods 200cell cats, Cargraphic mufflers, 3.8L manifolds, ipd plenum.

@Schnell thx for the link I think I got most of the data right

Be careful, all you are doing is trimming the safety margin that the factory put into the stock tune. If you engine is near stock, leaving the tune alone is good idea.

I used an Apexi Neo back in the day to tune my supercharged project car. As Imo000 remarked, you can do a lot of damage with a tuner...especially if you don't have a wideband to keep an eye on actual AFR (post-cat O2 sensor values are useless). I can't think of a single person I knew during that phase who didn't pop a motor in the process - and we were the "responsible" guys who actually bothered tuning. I use a Hypertech programmer to mess with the shift points and transmission pressure on my Corvette - but I won't go there with the 996. Post up your "pull" results - it will be interesting to see how the software dyno compares to actual 996 dyno sheets.

Well road dyno and roll dyno will be difficult to compare. Both data inputs are subject to different assumptions and different fault margins. So I doubt if they have any statistical value at all when compared. The advantage of a road dyno is you can eliminate the heat soak of the MAF which is a crucial factor in dyno-ing in static circumstances. Don�t underestimate driving wind. It cannot be compared with the force and flow of some ventilators. I followed the intake temperature for 25-30.000km in various circumstances and saw how fast it rises when driving speeds are down and the spoiler is not been up for a while. Also how long it takes to drop again to steady state when driving again. No experience with how it behaves on the dyno with artificial airflow. I am afraid that most of them will fail to simulate the real driving wind conditions with an engine in the back of the car! But again I only can make this from my own common sense and my engineering background. I cannot level my knowledge with the real pro dyno experts. As to safety. The exotic options are not my intention. But will check how it goes with the MAP functionality and eventually eliminate the less precise MAF. Further the standard ECU safeguards are untouched. I realize it is pushed more to the limit. Maybe lifetime is sacrificed a bit. The sooner I can move to my 3.8 or 3.9 or ditch it and go GT3 :grin: