Thread: plotting dynos from vbox data
03-18-2010, 03:56 AM #1Member
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plotting dynos from vbox data
Here are some spreadsheets I made that allow you to copy/paste vbox data and create dyno graphs. It works by calculating the horsepower required to accelerate at that rate, overcome wind resistance, overcome rolling resistance, and travel over that slope. It is as accurate as your inputs -- get a local weather report, enter in the weight within 50lbs, use the correct Cd and frontal area -- and you've got extremely accurate results. Start to estimate and the results will vary accordingly.
Keep in mind that "dynojet" horsepower figures tend to be inflated. Those overseas have long known this, but it still can be an ego check if you see that you're making 10% less power than you expected...
Open Office: http://www.mediafire.com/?djjqynmuyzw
MS works: http://www.mediafire.com/?tu11wo0fnnj
If you don't have a spreadsheet installed on your computer, you can use open office calc (available for free: http://www.openoffice.org/ ). It's what I use just because half of my pc's don't have excel and I hate having to switch computers...
When you open it up, it should look like this (sorry in advance if screen shots are too big for some monitors):
You will only need to enter data into the red boxes (green box is optional if you want to graph rpm instead of speed). Don't touch anything else unless you know what you're doing...
Now open up the Vbox software and load your run. I'm using and old beta version of driftbox tools software so it may be a little different (you can DL my version here if need be: http://www.driftbox.com/download/DriftBoxToolsBeta.zip )
Here I'll be demonstrating with a pump gas run for a HPF stage 1 car (actually stage 2 -- but without meth):
Under the "graph data" window, make sure Speed (mph), Height (feet), and Distance (feet) are checked (and nothing else). If the units are not in mph/feet, you can change the settings under "options" --> "units of measurement."
Now move the cursor to the start of the run, click "edit data" and "cut all data before cursor" (you can also hotkey shift-x):
Now move the cursor to the end of the run, click "edit data" and "cut all data after cursor" (or hit ctrl-x):
Now click "export" --> "chart" and a TeeExportForm dialogue box pops up. Click the "Data" tab, and make sure format is "text" and delimiter is "tab"
Click save, pick whatever name you want -- just make sure you know where it saved to (I prefer the desktop). Now open that file in notepad/wordpad, hit ctrl+a (selects all) and ctrl+c (copies):
Then go back to the open office calc spreadsheet, click on cell A2, and hit ctrl+v (pastes). A pop-up window will appear -- just hit OK:
Most of the spreadsheet should now automatically fill. Now look at the other red box and make sure the values are correct for your car & the weather at the time of your run. The e46 M3 has a Cd of .32, the frontal area is somewhere in the 22-24' area, weight is 3500-3600lbs + turbo kit + driver. For the weather I go to wunderground.com -- type in "Portland, OR" scroll down to "history & almanac" and put in 11/29/09 (when I believe Chris made this run). At 3:53 that afternoon, I get:
From the vbox data, I see Chris was running on a 30-33* heading (NNE) so the 6mph WNW wind was pretty much at his side. You can leave headwind as zero, or do 1/2 of the wind (since x-winds do add drag). 2.6mph is nothing, but I'll put it in anyway. Pressure was 30.33, temp 43, and humidity 74% For the Green box, these gear multipliers are about right for e46 M3 stock gearing and typical slightly larger (diameter) rear tires although feel free to adjust them to your specs:
If this run had been done over multiple gears, I'd probably just plot speed vs rwhp. To do this, just highlight cells AA9 - AD9 and scroll down until you get "#DIV/0!" -- then click insert chart (and follow the steps under "graphing" below).
But since this run was all done in 4th gear, we can easily get rpm (and from rpm & HP -- we can get torque). So scroll over to AF10, highlight the cell, type in "=$I$14*B10" -- then hit enter. Click back on AF10, right click copy, then click AF11 and drag down as far as AG has valid data (in this case AF 167). Right click again, and select paste. This section of the spreadsheet should now be filled in (the torque values specifically).
highlight all of the cells (including the first row with the titles) you want to graph, click Insert --> chart. A graph appears with a chart wizard. Select "XY (Scatter)" and "lines only"
Click next, make sure "data series in columns" and "first row as label" are checked, then click next again. Step 3 -- just click next again. Step 4, chart elements. You can add a title ("Terry HPF M3"), subtitle (Pump Gas (no meth)), X-axis title: RPM, Y-axis title: RWHP/RWTQ. I generally like the legend on the left, and I like to check display grids for X and Y axis:
You're pretty much done unless you want to spend a little time expanding the graph, changing the scale of the axis, changing the color and thickness of the lines, etc. Here's what I come up with:
I've used some smoothing techniques, but these graphs will tend to be a little more bumpy than most dynos. In this case, the HPF Stage 1/2 on pump actually has kind of a bumpy power curve anyway (it doesn't look quite as bad since the Y-axis is scaled to 700 instead of 500):
Other notes: I added SAE and STD correction factors. I'm not really a fan of using correction for FI vehicles (especially turbo), but everyone seems to want SAE. Keep in mind the "actual" numbers are what the car truly made that day -- SAE/STD are basically an educated guess as to what they would make under those preset atmospheric conditions.
Terry Race (no meth):
Scott's 4th gear pull last year:
Compare the above with the dynojet runs, and you'll typically see +100ftlbs at 4000rpm (from turbo being able to spool much faster on the road), but also 20-40hp less peak hp...
Scott's recent 5.83 60-130 run on the new HPF stage 2.5 tune:
Scott's friend (TT viper -- estimated weight 3650, estimated temp 60* estimated pressure 30.3)
Last edited by spdu4ea; 03-18-2010 at 04:26 AM.
03-18-2010, 04:42 AM #2
This is very well done and highly informative.
It is also explained in a way someone who is not mathematically inclined can still understand. Well done!
03-18-2010, 02:55 PM #3Guest Vendor
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