meaning of "grunt" when it comes to towing

The title of the humorous story is "The Sun got stuck"

“I don't suppose you could give us a tow, could you, sister?”

Luna's eyebrows shot up, “How? With what? The sun's 400 times larger than the moon, and even if I could give you a tow, it'd take me 8 light minutes to get there! And besides, I may have lowered it and put a supercharger in, but I'd never have enough grunt to tow it! Sorry, sis, but you're on your own. You can fix it, can't you?”

I tried the usual (Wiktionary, Merriam-Webster, The Free, Dictionary.com) and none of the definitions (foot soldier, sound, menial worker, fish, dessert), seem to match this kind of usage. What does grunt in this context mean?

From the Oxford Dictionary:

3 [mass noun] British informal mechanical power, especially in a motor vehicle: what the big wagon needs is grunt, and the turbo does the business

Grunt is being used to describe pulling (or towing) capability. I found it in this article relating an entry in a tractor pulling competition:

He says it is about having the tractor with the most grunt, but adds that a lot of skill is also involved.

In this context, grunt means power or force. In the context of engines in general, grunt often refers to the amount of torque that the engine can produce.