Originally Posted by touringbubble

the big difference is cylinder pressure. Even at the same boost/load level, cylinder pressures will be higher with a cooler, denser air charge in the winter. This can cause knock even if you don't leave the tuned cells.

The evo does have a temperature compensation map that can be tweaked. I've modified it on a few vehicles and have seen a benefit from it. However, even with a modified compensation map, that dense air will reveal any over zealous areas of your tune.

Many have reported knock on the stock tune. The stock tune was designed to be good for as many weather/location variables as possible and therefore has a large margin of safety. This method tries to ensure that the car runs well in nearly any climate or altitude, but also leaves a lot to be desired power wise. We tuners could easily create a similar tune with big safety margins, but it would likely be no better than the stock tune.

When you tune the car, you effectively reduce the enormous margin of safety that the stock tune has and narrow it down to match the specific car and environment. This is why drastic location changes (texas to colorado for instance) require a re-tune.

But, when it comes down to it, a good tune will not knock in the summer or winter and will make power. You should not "require" a retune unless the environment drastically changes (elevation, humidity, etc.) or the car changes.