What it Does
Street Dyno is a computer program that uses your ignition signal as an input to derive horsepower and torque curves. If you tell the program how many cylinders you have, it can easily determine the RPM of the engine from this ignition signal. By calculating changes in your RPM, along with your gear ratios, weight, and a few other simple parameters, the program will determine your horsepower and torque curves.
Where to get it
Street Dyno is available as a free download from the following web site: http://www.tweecer.com/StreetDyno/downloads.html . Take a look around the rest of the site to find out more about what street dyno is, and what it can do.
How to Use it
Toyota has conveniently given us an ignition output for us to use, which is where this signal is taken from. This output is located on the side of the diagnostics box in the engine bay, and is labelled "IGN". If you use a sound recording program, you can record the ignition pulses in a .wav format onto your computer. You must build a voltage divider as shown below to record this on your laptop computer.
In order to save this file, you must choose a sound recording program. There are many available for free on the internet. The software I use is called Goldwave, which is available as a trial version on from Goldwave's web site. A google search will find many similar programs. Windows also offers a very basic program that allows you to record sound files. It is called Windows Sound Recorder. Some people have used this with success as well.
You must create a voltage divider circuit in order to record the igntion pulses onto your laptop computer. The makers of Street Dyno have provided the following diagram which correctly shows how to build this circuit. The "input" is the IGN output on the diagnostics box, and the "chassis ground" is connected to any metal point on the chassis of your car. "V out" goes to the tip of a 1/8" mono phone plug, and the "Gnd out" goes to the outer edge of the mono plug. Make sure to solder your connections and use heat shrink or electrical tape.
Once you have the voltage divider circuit built you are ready to make a street dyno run. Plug the mono plug into the microphone input on your laptop, and the IGN and Ground inputs in the engine bay, and you are ready to go. Keeping your revs fairly steady at roughly 1500 rpm or so, press the record button on the sound recording program. Then quickly press the gas pedal to the floor and allow your revs to get to redline. Push in the clutch, and slow the vehicle to a stop. Allow the program to time out the recording, or stop the recording at this point. In theory you can do this in any gear, however I like to use 2nd for safety. If you tried a 3rd gear run you could be reaching speeds upwards of 150km/h! Not so safe when you are trying to keep an eye on your laptop at the same time.
Saving the file requires special attention, or the graph will not display properly. First you have to edit the run so that you have saved only the relevant acceleration through the gear. Delete everything after the point where you push in the clutch. You can listen to the file and it will be fairly obvious where this point is. Once you get used to the program, you won't even need to listen to it. When saving the file, you must be careful to select "PCM unsigned 8 bit, mono". The screen capture below shows an edited .wav file using a program called Goldwave, to give you an idea of what your file should look like.
I recommend making several runs in case that some of them do not work out, and so that you can determine if there are any differences between runs. Sometimes a missfire, ECU knock response, or even a bump in the road can mess up your run.
After you have saved your files, you can open up Street Dyno and upload the .wav file. Enter in your parameters, and save that config file as required by Street Dyno in the readme file. Click on the lightning bolt, and a graph should appear. You can now play with the Triggering Options until the graph looks fairly smooth and accurate. I usually use 0 per cent loss to the drive train, however when looking for BHP, the generally accepted figure is roughly 20 per cent for the GT-Four. The following image is the final product. Take a screen capture and save it in photoshop or paint, and show it off to your friends!
You might also find the following sites useful:
http://member.newsguy.com/~gtfour/dyno.htm
http://website.lineone.net/~gtfour/streetdyno/dyno_results/dyno_results.htm
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