Brake pressure drop while down shift

sawill629

I have my used 09 370Z sport 6MT for 6 mths 35k. Does any one have this symptom or any advise ? Thanks in advance.

Change all fluid before the track day
fornt Hawk DTC 70 rear DTC 60
power slot (slot) rotor F/R ( no brake cooling duct )
SS brake line
OEM suspension
CB exhaust / test pipe
front camber arm

When I am at the local track day ( mission raceway). squeeze the braking under high pressure (like 70%) downshit while release the clutch. I can feel the brake pedal pressure drop down a bit. while the pedal drop the car wasnt slowing down as it should be ( could be scary ). No matter under S-mode or not still the same. try to breed the brake and do another test. still the same. normal daily driving or light pressure under track condition (50%) brake feel like normal. I guess thats not ice mode since the pedal being soft instead of being hard. I dont feel ABS kicking the pedal. any advise ???

another question is while I am testing the brake for the 2nd time I do 8 laps ( 2 laps warm up 6 laps more aggressive in total 16mins ) after that I am doing a cool down lap. I experience my first brake fluid boiled which i am using Motel RBF600 already.( my lucky day). no brake. sponge on pedal. I know different track and brake skill will total affect the temp of brake fluid which I have been doing this race track for 10 yr. with my previous STI I have no problem at all for a full 30 min. Do you think brake cooling duct will help ?

Please forgive if I am making story long.