[Svartalfiar]

When vaporized, gasoline is about as explosive as an equal mass of dynamite.

That depends entirely on the concentration. Gasoline vapor is ONLY explosive when in gas-air concentrations of ~1.4% to 7.6%. If there's more gas vapor, it can ignite and burn, but not explode. (Note this assumes standard air and it's oxygen concentration.)

At ideal concentration, however, fuel-air is actually around 2-4 times more explosive than TNT, depending on a few other factors.

[yefragetuwrabrumuy]

Gasoline has a bad habit of moving from a less explosive concentration to a more explosive one as a secondary explosion. It can work both ways to get to the bracket concentration you described, that is, either increasing or decreasing the concentration until boom. It is fickle.