The Gryphon and speedo will always read the same (actually, the speedo will be about 2 mph higher due to a quirk in the way Ford does things, according to Bill). They BOTH get their input from the PCM, which has been programmed by the Gryphon to interpret axle revolutions to determine speed and distance. The fact that they agree with a GPS, though, says the overall effect of the gear and tire circumference settings is producing correct speed and odometer values.
But, and this is a big but: Both gear and tire size COULD be wrong. I'm positive the default values in the Gryphon have nothing to do with what's in your truck. On the f150 forum, someone had 3.55 gears and the Gryphon said he had 3.73 gears (and he had "funny" shifts). I think 3.73 might be the default gear ratio. The tire size on mine always defaults to 2356, but my actual tire circumference, accounting for "squish" is about 2481. Since my gears ARE 3.73, if I don't set the tire size manually, my speed and distance values are about 5% lower than actual.
And, I don't recall the MAX RPM default in the canned tunes but I know it was lower than 5400. The MAX speed is set to 99 MPH, by the way.
All these things are adjustable in the custom options menus. You select something, such as Tire Size and hit Enter. You'll be shown what the Gryphon is going to insert into your PCM when it "tunes" it. If you don't like what you see, just use the up or down arrows to change the value, then hit Enter to set that new value.
I doubt you can hurt anything unless you do something stupid like advancing the spark on low octane gas, or, possibly setting the Rev Limit to a very high value and then standing on the gas pedal.
You can actually go through all the settings without changing anything just by hitting Enter at each and then hitting Enter again to accept the value once you've seen it. When you're through looking or customizing, hit Enter on the "Done" option and you'll be told to turn the key off and then back on.
If you've gone through the custom options and looked at any of them (or changed them) the programming process will take quite a bit longer than if you just skip the Custom Options step. Don't worry, just make sure your battery is healthy and that your headlights, AC blower and radio are off to minimize battery load. Don't do it in really cold weather either.
Hope all this information helps. I'd be more afraid of damaging the truck through hard acceleration and high speed, rather than through playing with the Gryphon.
And, I hope Bill chimes in here sometime to say I haven't been leading you astray.
- Jack
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