To explain Mike'* comments a little more, normally aspirated motors are more susceptible to the effects of low air density. If you take a look at fighter planes from World War Two, you see the addition of various power-adders to planes as the war progresses. Aircraft developers started seeing the benefit of supercharging and turbocharging in order to make engines perform better at high altitude. A forced induction setup will not feel the effects of thin air as readily as an NA motor, for the simple reason that air is being compressed and blasted into the intake manifold. The L36, much like the earlier fighters of WWII, is normally aspirated, and is completely at the mercy of atmospheric conditions. Cool, dry air is more dense than warm, moist air. If you start tuning your car to the ragged edge for certain conditions, you'll notice it feeling weaker on days that have thinner air. That'* why Mike is saying he had to re-tune from season to season. Winter air is colder and almost always drier than summer air, and a maxed-out tune in the winter will often involve different fueling than a maxed-out tune in the summer. From the factory, our cars are designed to adapt to a plethora of different conditions and air densities, but when you start adding parts and modifying the PCM code, you affect the car'* ability to "roll with the punches."
I have certainly noticed the effects of seasonal change in my car. The temperature variation alone accounts for a lot of it. But I think Mike is right in saying that it'* more noticeable in a modified car than a stocker. It'* nothing to be worried about, either. I had my car dyno tuned in humid, 65 degree weather in Ohio, and then I promptly moved to Arizona where the word "humidity" is a foreign language and 65 degrees is enough to make you wear your winter parka. I simply babied the car in the heat of the desert summer, and I'm now enjoying the power that comes with the dry, cool air of the desert winter. You don't have to re-tune for the seasons, but you'll notice that changing conditions will have an effect on the butt dyno.
1997 SE w/SLE package
"White curse? I think it'* more like.... WHITE FURY!" - MyLittleBlackBird