Flat floor, diffuser and hot air

[RH1300S]

HI,

I am a huge fan of F1 and I have watched almost every race since 1989. I think there is less than 10 that I have missed since then 

I am reading this forum for two years at lease and it was very helpful. I am currently building truck day car, mid-front engine with rear wheel drive, around 950kg with driver and 250hp engine and I need some help in terms of flat floor, exhausts and cooling. Car is equipped with flat floor and rear diffuser.

Can you explain me if there is any advantage/disadvantage of directing hot air from radiator under the floor. Radiator is about 50 cm after the front bumper and I can choose to direct hot air through the bonnet or under the floor.
The same question is for exhaust gasses. Should I put them under the floor or at the rear of the car above the diffuser?

Thanks for your help and understanding (I am not an engineer)

Regards

Would it make more sense to look at prototype sportscar design? Especially older ones where they had front radiators, they let air from the radiators (heat exchangers really) out onto the upper surfaces of the car - AFIK this was to bring some higher pressure air from infront of the rad onto a low pressure area on top of the nose, which helps air through and also helped reduce lift. Likewise, the vents you see above wheel arches are there to reduce lift as they let high pressure air from around the wheels exhaust into a low pressure area.

I am thinking that you would probably get more benefit from looking at areas on the upper body where you can reduce lift or even add some downforce (wings?) rather that get too hung up about underbod areas - which seem to be very sensitive and hard to tune. At least with upper body devices you will find they are easier to change/adjust.