how fast will a vx-18 engine go? in a car? and in a truck?

It all depends on gearing, which car/truck.  The vx is not a real powerhouse but i find it to be super reliable and a long lasting engine.

but still with everything stock, how fast will it go on a car and on a truck?

lol, it depends on the car or truck, a 2 speed taipan will be faster than a single speed viper. 

On a car i would say 40mph and truck about 30mph

i think that's impressive... thanks bro

The only true way to find out how fast your car or truck will go is to radar it yourself. Different elevations will change top end speed. And it does not matter what nitro content you use either. The higher the nitro comtent the quicker you will hit your top speed. Nitro content will not give your engine more rpms. When its maxed, its maxed. We tested 20% tuned to 250 degrees and the cen car ran 49mph consistently. We put 33% fuel and retuned engine to 250 degrees. Again we hit 49mph consistently, but it got there quicker. You can buy a radar gun for about $79.00 on ebay. Just search radar gun.