The additional power from the reflash is generated by modifying the fuel, ignition and cam angle. There are 10 tuning air pressure positions from sea level to vacuum. Hondata tunes at sea level.
As you rise in altitude, the air pressure reduces. This does not affect the fuel and cam angle changes, but it does affect the ignition changes . At around 8000 feet altitude there is no difference between the ignition timing for a stock and a reflashed ECU. At around 3700 feet, the ignition changes are a around half that of sea level.
Altitude changes do not affect the improvement Hondata has made to rev hang.
so you are saying at sea level you should get the gains they claim? and even if that made sense he should be gaining around half since hes 4k above sea level. yet he said he got 2hp but by his graphs he went from 177.7 to 178.5 which is 0.8hp. I was pretty sure i was about to buy this reflash for my 2012 si coupe and even though where i live is only 300ft above sea level but now im not too sure i want to buy this unless i see some other people actually getting somewhere close to the numbers that were claimed