I have been thinking of fitting a rear diffuser to my car and seen several posts discussing this. However I am not clear on how big to make the diffuser and how to fit it. If I make it to cover the whole of the underside of the rear area will I need to cover the tunnel . I am thinking that the rear diffuser will become a scoop and fill the rear panel void with air.

I have a rear diffuser on my car that stops at the rear bulk head behind the seats area. Under the engine bay and tunnel are left open.

My current thoughts are the resistance for the air to get up and over the rear diffuser, to sqweeze past the diff, past the fuel tank and through the gaps out the back is a lot higher than just carrying on under the car.

From the track days I have done I think my car keeps up with other se7ens and full bodied kits at higher speeds which is great. Especially as my 4age is approx 150bhp and I often end up playing with cars that are 200bhp CEC or becs. I have no reasoning behind this other than I have half doors, half tonneau and the Striker is smaller than most cars.

I have done some changes to my engine cooling and will be seeing how they work on track. If all is good I will be flat flooring the engine bay and tunnel.

a full flat floor would be the best solution

as for fitting, i made some alu brackets that sit over the chassis and bolt either side through the diffuser/splitter
like this


the rest of the floor is riveted on

front of the splitter has stainless tie bars