Every time I measure my hp during hot days I see a dcrease of 10hp.

Today I felt my car very slow, the weather temperature is 90ºF / 32ºC.

Does the ECU change the map to a conservative one during hot days?

 

Yes, you will see a decrease in hp on hotter days. The colder the day, the "denser" the air becomes, and you can get more oxygen into the engine on a mass basis. Add the appropriate amount of more fuel, and you'll make more power. On hotter days, just the opposite occurs. When you heat up the air (air is a gas), it expands and it's mass per unit volume (lbs. per ft3 for example), and you just can't get as much oxygen into the engine for comustion.

It's not that the ECU changes maps, it's just accessing more conservative areas of the same map based on the crappy weather conditions. Where the heck are you at that it's 90F???? It's Christmas!

 

+1. Over in my kneck of the woods, the temps are below 0 and my car runs VERY good. Seems like more power and the engine stays VERY cold. When i let off the gas, i can see the temp needle drop a little bit and my TT shuts the car off in seconds after a 10 min drive home from work in the 5th gear 3900 rpm range, with a few quick pulls inbetween then.

 

Is there some relationship between hot days and colder spark plugs?

I mean, Will a colder plug increase/decrease the performance during hot days?

btw, South America, starting summer season.