last couple of time i ran on 25" slicks, i noticed that when i shift into 2nd gear, b00st would fall off and slowly build back up to full boost. if i run it on street tyres this does not happen. what could be the cause of this?

 

you are probably shifting too early... in first gear with a higher horsepower car you need to feather the gas in order to fully ride out the gear... if that is your case this happens because you are spinning the slick and when you shift into second the slicks grab and you bog down... took me a full season of seat time to get first gear down...