I've hit 300bhp too but that was because it was 90*F one evening then the next morning it was 50*F outside, so the ScanGauage went crazy, plus it was showing me getting lower 20MPG's highway.
After I reset it, the BHP's were more realistic and MPG's.
I personally still am deciding if it's worth it, this is why I haven't advertised it bigly yet.
It did help you resolve the crank issue
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Now once you tune the MPG offset % it seems to be showing it correctly. In my case I've noticed that my City offset is about 28% while highway is in the Negatives. So that means my gas is some how disappearing in the city, aka some kind of a leak some place.
I always use the Intake Air temp and Coolant temp. This way I didn't have to buy separate gauges for the Coolant temp.
Battery Voltage is a very useful one, helped me show that my parent's Maxima's battery is about 50% dead.
So technically the ScanGauge has been pretty good for everything but the MPG part, but thats because there is an internal problem with my car
Now back onto the BHP's.
I did notice that BHP's are not 100% accurate, but fairly close at best probably 5-10% BHP off, thats like 2-3 WHP off (nothing major).
Like I did notice that the BHP feature would over shop the BHP's if you go little pass the redline. (7300 RPM)
I tried using it on my friends 98 Camry, by book it has 133BHP, ScanGauge showed 130ish, and 139 very close/past redline.
1996 Maxima by book 190bhp, but I've been in 205 range mainly (a person on this forum did mention that those models came with 200+ish)
So it might be a few off, but when I can feel the power difference between 180BHP and 206BHP, like a world of a difference, the car feels like 200+ bhp haha
Sorry for the long post