The front diffuser is a separate piece that I havnt made yet I'll have to put the drawing up of the separate parts (floor and front diffuser, monocoque, side pods, front and rear fenders and the bodywork in between the rest of everything) I don't know which part you mean by air vents behind the front wheel (i'v added way too many vents there lol) the vents on top of the wheels are going and being replaced with the conventional regulation hole. The vent in the side of the front fender is on pretty much all the LMP1 cars. So you'll have to show me where you mean
. The whole point of the double diffuser was to suck in extra air that would have just hit into the bottom of the rear wheels. The turning veins would be in the diffuser section right? When I designed it I did it more on looks than anything else to be honest
And at the back the turning vanes seem to be "moving" into the middle at a very steep angle. this would concentrate the air flow towards the middle and increase preassure/restrict flow. While a bit of curvature is probably wanted, due to having to cope with the tires being a bottleneck, at the end of the diffusor the vanes should be straight. I have no idea how one would draw this, so if you want it to stay the way it is, I am not going to complain. 
