Algodoo

I don't know if I can really help you without building it for you.
If you are having trouble finding a good engine design/concept, check out my "super engine". It utilizes collision engines, spring engines, and thruster engines; all in 1!
As for the gearbox, if you want it to be automatic you'll need scripts.
If you want something simple an 8 circle design would be great.
You'll probably have to scale up the engine quite a bit if you want the van to have realistic acceleration.

I've learned this:
1. Set you piston inetriamultiplier around 5x-10x, it keeps it them from spinning around and getting stuck sideways.
2. Try direct linkages (the 4 bars with 2 hinges each on 2 linked circles) but you probably know about those.
3. Lower you densities for better speed, but keep your center of balances straight with weighted boxes.

@Ky13harbor9: Thanks for the fast response and your tips.
If you want to you can build one for me, but I won't use it in my scenes because I want to make something myself. However if you build one, I could use it as a sample engine. But it is your choice if you want to or not.

I already knew about point 2, but never got it work properly.

And what densities do I have to lower?
I gues the piston housings and the pistons themselves.

Thanks for point 1, I didn't know that!!!

By the way I think I am going to choose a simple old fasioned circle design.
Because I can always make it (semi-)automatic if I want to.

Or you can get the killers a bit more away of the spawners and use Attraction-turbo?

I tried putting the killers a bit more away, but that resulted in a unstable engine.
But I'll try attration-turbo to see if that works.
To be honest I never thought about that.

i made it a ton better runs around 57 rads/ sec now stable. contact me if you want it.