Did some interesting quickie calculations with online 1/4 calculators, not truly accurate but gives a good enough ball park to judge when HP, weight, 1/4 times and trap speeds are known.
At McLaren P1's listed weight of 1395kg and 903HP, I added a 68kg driver to the equation and uses 2 different site's calculators and average the results.
On paper the P1 is suppose to do a 8.87@ 151.54. Now the Road & Track's time is way off on both count.
Since ET do varies depending on launches, the trap speed is a more consistent measure of car's HP. To adjust 2.64 mph difference, the engine either is down about 50HP or the weight is about 90kg heavier than listed.
While R&T did the run in England on a slightly damp track, that might account for some of the traction issue, the engine on the other hand has to be making at least 903HP if not more with the cold air.
Maybe the 1395kg is the dry weight of the car, but does all the fluids in a car weights 90kg?
Also did a calculation with the 918's numbers based on the 1640kg listed weight of the Weissach car with a 68kg driver and 887HP.
The averaged number is 9.4 @ 143.27. Close enough to the rumoured time of 9.65.
Also consider the 5.63mph difference in trap speed between the measured P1 speed and the estimate 918 speed.
For rough calculations by dragsters, every 20HP equals 1mph and every 75lb, or around 34kg is also a 1mph.
If the P1's true weight is 1485kg instead of 1395kg, then it would be about 155kg lighter than the 918 and that alone accounts for about 4.5mph, plus the extra 1mph from the 16HP advantage.
For comparison, I plugged in the 12C's number to do a calculation, but only the listed weight plus driver, so 1467kg and 616HP. It averaged out to be 10.09@ 133.49mph. Extremely comparable to the 10.55 @ 134.56mph gotten by a mostly stock MP4-12C last year which only has an exhaust upgrade. That specific car weights 1414kg with 1/4 tank of fuel.
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