I used my friend Allen's blogpost as a guide on how to speed match. http://thelittlerockline.blogspot.com/2012/04/speed-matching-locomotives.html
A special thanks to Allen for putting this together. It was pretty easy to follow and understand once I got my hands dirty working with it.
So, I have two locomotives. First, the Atlas Rock Island GP38-2 #4303. Second, an Atlas Grand Trunk Western GP40-2 #6412. Both by the same manufacturer, but run night and day different.
So, I placed both locomotives on the test track and let them run for about 15 minutes each before testing. The Grand Trunk was geared for "Nascar" running 83 smph compared to the "Driving Miss Daisy" RI GP38-2 running 36 smph both at half throttle. Top speed for the GTW unit was a smoking 149 smph compared to the RI unit at 92 smph.
Using Decoder Pro 3 and JRMI, I connected my MacBook to the NCE system. I read in both locomotives and created a profile for each.
I made a few initial changes to both locomotives. I turned off Analog Mode for both locos as I don't plan on using them in standard DC. I checked to ensure CV3 and CV4 were set to 0 to turn off momentum. I turned off BEMF (CV57 on Digitrax, CV61 on TCS).
On the Speed Table tab, I started off by selecting "Use Speed Table (CVs 67-94)". I started off with 0 and the max speed for the high end. I selected "Log Curve" which generates a natural curve for power to the locomotive. I tested. Nothing moved when turned to speed step 1. So, I bumped it up to 5. Wrote the changes ("Write full sheet"). Still no movement. I changed it to 9 and found movement. I then adjusted the high end voltage down, selected "log curve" again to change the speed table values between the low of 9 and high number), wrote the values to the decoder and tested until the top speed was around 70 smph for both locomotives.
Once both locomotives were running at nearly the same speed, I checked the mid-range setting at half throttle. I had to adjust the GTW unit slightly. It took a big of trial and error to get it right, but overall not bad. If I had everything sitting at the workbench, it would have been much easier. My setup required me to get up and change the settings on my laptop and then walk back to the workbench to test again.
You can see the speed tables for both here below. As you can see the GTW unit has a much lower max speed.
Now, at half speed, the locomotives were within 1 smph of each other. They run very well together at all speeds.
I need to work on speed matching all my locomotives so any of them can run together instead of my typical matched pairs, but this is a start.