Just my two-cents, but I couldn't sleep last night speaking of this ?
Before thinking about whether the BF1's engine could work upside down, we should wonder about the downforce produced.
I don't know the exact amount of downforce produced, but I've heard readind those pages that at 161 mph, the BF1 can produce enough downforce to equal.
So basically, when driving on the roof at 161 mph, the downforce created will be equal to the weight, with the force going upwards. The only problem is that is the downforce equals, the sum of the forces exerted on the BF1 will be equal to zero (value of weight + value of downforce -which is negative- = 0).
This won't make the BF1 able to stand on the roof, because if the weight is zero, the force exerted on the tires will be equal to zero, as if the tires had nothing on them to keep them stick to the ground (even they will be weightless). Which means that at 161 mph, the tires won't have enough grip to keep pushing the car forward, so the speed will reduce drastically (because of the excessive air resistance needed to create the downforce).
The result will be the car falling down on the ground, upside-down, resulting in the death of the driver, and the loss of a 20 million car... (omfg)
So, the car, in order to stay on the ground would need at least to create as much downforce as two times his weight (to make the tires have a grip on the ceiling). And in order to be driven like normally on the ground, they would need to create downforce equals to three times its weight.
How to do this ? Two options : Speed, or more wing angle.
In both case, a more powerful engine is needed. It seems obvious for the first option. For the second, more wing will create more air resistance, so a more powerful engine is needed to give the same performance with an increased air resistance.
OR, third option : getting Alonso, Hamilton, Massa and Kubica drive steady at 140, 150, 160 and 170 mph in the tunnel so that the driver of that BF1 will take their slipstream so counteract the air resistance and accelerate faster :P