hey guys I had this idea yesterday. I was reading thro pgmfi and I saw them mention using accelerometers to aid in "butt tuning" I looked these tools up and there alot of money. so i thought to myself why couldent I use a phone app. its possible to calculate hp from distance traveled and time. would also have to take in to account the weight of the vehicle and a good guess at the drag of the vehicle but I believe its possible with a really good program that updates multiple times a second. sure this would not be a end all solution to the dyno. but you could use it as a tool when you dont have one and get a better guess at things. so does anybody see any flaws with my idea? i dont know how to code myself but I was thinking of pitching the idea to a couple freinds who could.

 

the accelerometers in phones typically arent accurate enough. We tried doing this and the interference (noise bumps and turns) made it inaccuarate.

 

If you're able to tune, you're able to generate data logs, no? Put together an Excel sheet that calculates differential acceleration from a .CSV of your logs (or use Virtual Dyno)

 

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I have been using virtual dyno for a few years now. I even did a pull and compared it to my dyno tune and it was within a few percent with the same curve which is pretty good in my opinion. make sure to use the same road and try to have similar conditions (iat etc) to reduce other variables.

 

The trick with it (and any other street tuning) is the repeatability.

- Do your pulls on the exact same stretch of road.
- Lay down a start line; this is where you will go to WOT on your rolling start. Start at that line from the same rpm, every time.
- Do a pull in both directions of your stretch the first time you use it and overlay them. This will show you in you have any grades affecting your data.
- Factor in the atmospheric conditions at that location. They're in the calculations for a reason.
- Cold, dry days make more power but have more aero drag. Hot, humid days make less power but have less aero drag. When moisture content is up, there is less room for "air" in the air
- Weather Underground is your friend, or consider buying a Kestrel (if you plan on doing this often): - No running on windy days. This should be obvious, honestly. I prefer to run at night... Less traffic, winds are typically down, and since it's cooler out with no sun, it's easier to keep engine temps stable.
- TAKE NOTES!!!! Number your calibration files and save as every time you make a change. Start an Excel sheet that describes what you changed for each pull.

I don't really find it important if the numbers compare to a dyno, but it's nice if they do. I'm only looking for the deltas between changes to tune the engine.