Heat Crash's base power is relative to a range between your weight and your opponents weight. To put it simply, if your weight is **at least twice** that of your opponent's, the move's base power will be **40**. If your weight is **at least twice but no more than thrice** that of your opponent, its power will be **60**. On the chart below, "r" represents your weight divided by your opponent's weight.

5 ≤ r = 120

4 ≤ r < 5=100

3 ≤ r < 4=80

2 ≤ r < 3=60

r < 2 =40

To answer your question, Pignite weighs 122.4 lbs. and your opponent (whoever that might be) weighs 37.8 lbs. Since the move is STAB and has a base power of (122.4/37.8 = approx. 3.2; **3 ≤ r < 4=80** ), you'll be doing damage of **120 power**.