Found something really interesting in my Laguna Seca data. I took 2 laps, one from last year and one from this year and compared them. Both laps are within 1/10 of a second from each other. The 1st graph uses my actual start/finish line as a base. The blue graph is this year. Red is last year. Look at the dip in speed on the front straight. It looks like my car was not performing in 4th gear under load going up the hill. If you look closely to last year

 

I agree with heat theory. Occasionally my car some what struggles in 4th gear. Almost seems like to doesn't pull as hard as it should. Now that I think of the times it happened it was pretty hot outside. The car would run normal in any other gear but 4th.

 

there could be underlying factors in this....

 

Heat may have been a factor. It was 90 that day vs. in the 70's last year.

 

I bet it was the heat. My car runs better in the morning and evening. The air is more dense when it's cooler allowing your car to perform better

 

I've known that hotter temps will have an affect, just thought that effect would be more across the board rather than just 4th gear bewtween 85-90 miles per hour.

 

the difference is due to change in air density form the heat and/or barometric pressure.