What technic vehicles are built to scale for 75114 First Order Stormtrooper?
Obviously The Lego Group has not released any sets specifically designed for the constraction figures, but some sets would still be reasonably sized. I've never asked a storm trooper, but let's assume he is 6 feet tall, or 72 inches. According to Brickset's information, 75114 is "over 9 inches tall" That makes the scale for the figure about 1:8. 

Now bringing in the Lego Porsche 911 GTR, we find from its description that it is "22 inches long" The actual car's specs put its total length at 178.94 inches, which I have rounded to 179. So the car's scale is 1:8.14, which would mean that it is "to scale."

Now I don't have either set, so perhaps another user can provide photos of whether this figure actually fits in the car. I suspect it would not, which doesn't upset the reality of this situation. I'm not sure that John Boyega would fit in a $175,000 car in full storm trooper attire.

If the scale still bothers you, we might work with this actor's height at 5' 9" or 69 inches. That makes the scale for 75114 1:7.7 This would definitely make the scale believable enough if all you wanted a photo of the figure leaning up on the technic model. 

Additional info: 42021 and 42022 are not to scale; 42029 is close; 8070 is also worth looking into....

That gets you back to 2011. I may have missed some so please comment below if you see any I missed!