If real difference is 10-15 whp, then I cannot explain why the '17 bone stock cars had so bad times in the mentioned race. I agree that human factor is an important thing, but this was a proffessional class, the track is large, the conditions same and there were more than 20-25 drivers. In fact, the lap times are suprising close comparing to last year. I mentioned already that some drivers were complaining about issues in acceleration. Probably, they were told the same thing (10-15 whp difference) and they could not see it in reality.
Here are the cars of last year:
Here are the cars of this year:
