Problem with ADD TORQUE

I don't really know if this is a problem coming from Playmaker, Unity or PhysX itself.

Fact is, I add torque to the wheels of my vehicle, but there seem to be a ceiling to the power that can be added, and I'm EARLY hitting that ceiling.
In fact, my vehicle can't go past something around 80 Km/h (didn't check exactly, still have to make the speedometer, but surely it's not the 300 Km/h I need).

I tried to put 100, 1000, 10000 and millions, but it simply doesn't change anything past 100 I think.

My hypothesis are:

• Playmaker has a standardized ADD TORQUE action that applies the force to a point too near to the axis, so increasing the power doesn't really add up. This can be easily circumvented.
• Or, it's Unity to have this problem. This would be a little bit harder to fix.
• Or, PhysX doesn't "expect" that such high torque added to an object, so it's limited in this regard. If so, I'm f**ked. But I don't think it's probable.

Does someone have any idea about what's going on?
I'm stuck, because I'm making a racing game, not a pizza delivery simulation

You can download a build to see what's going on (ZIP file for Windows x64):
https://drive.google.com/open?id=1cn_2H1LOLC4BJcFpAJXoGI0426JM4YiO

P.S.: oh and before somebody comes up with this, of course I have put to 0 both DRAG and ANGULAR DRAG

 

Try setting your rigidbody's max angulary velocity. Here's the documentation for it: https://docs.unity3d.com/ScriptReference/Rigidbody-maxAngularVelocity.html