Algodoo

Use circles instead of gears, because gears are buggy and can handle less power than circles.
And you could use attraction-turbo, which basically means that you work with "attraction" to get more power out of it.
I learned all this from other creators when I needed help with one of my engines.

Maybe you can also try to position the pistons so that they both hit the scriptboxes at the same time (or with a slight delay between them).
This way you get a huge power boost instead of 2 small ones.
I don't know if it's effective on your engine, but it's worth trying because it works for me.

In my opinion thruster engines are easier for people who don't have experience with building engines, because they are easier to make and adjust then for example spawn/spring/bounce engines.
I tried to make a spawn engine too, but that project didn't end very well.
It couldn't even make a small and light test car move.

So, I made a thruster engine and that one works great in a car.
It produces max. 60 Nm, which isn't a lot, but it's enough to get a car all the way to 65 m/s (about 230 km/h).
I got some help from somebody else, who made the gearbox and made the car work. Because a engine alone is not enough to make it move

How can I made "Truster" Engines?

Check out one of my first cars with thruster engine: http://www.algodoo.com/algobox/details.php?id=60492

It's simple and it doesn't have a lot of power (25 Nm, I think), but it's a great engine to start with. The scriptboxes and all the mechanics are exposed, so you are able to see how it works easily.

However, I don't give you permission to copy anything, you just have to make your own.
But you can use my scripting as an example, because everybody uses this or a similar script.

Btw, it's not the same engine as I was talking about, because the engine I was talking about has three cilinders.
http://www.algodoo.com/algobox/details.php?id=63992
(The gearbox problem has already been solved, but I haven't uploaded yet)

You aren't allowed to copy anything from this engine either!
I hate people who steal other peoples stuff.