Saloon car underfloor venturi

[Tigermoth]

In my race series I have no restrictions on the underbody aero. I had planned on creating a venturi profile channel that runs with parallel sides, unobstructed from front to rear, 1.1mtrs wide over 4.75mtrs length.

Initial thoughts are to run with a 30mm radius on the front splitter at 80mm from the ground, curving down to 50mm from the ground at 900mm back from the nose, then flat at 55mm height for 1300mm length before tapering back up at 10 degrees in a diffuser over 2550mm.

I can run with side fences down to approx 15mm from the ground to partly seal the venturi and diffuser, spring rates will be appropriate to control ride height to a minimum of 40mm.

My question is, what can I expect the downforce to be from this set up and does my proposal sound reasonable or are there any flaws in the plan?

My maximum speed will be 160mph with the majority of corners being in the 70-100mph range.

thanks

Andy

[Cold Fussion]

2550 mm may be pushing the limits of the diffuser some what at that diffusing angle.



The left image is a chart from Belvins, and right image is from Katz.

[Tigermoth]

Thanks for your reply, this was going to be my starting point so I take on board your point on diffuser length and angle.

If one had a clean sheet and a rectangular 4750x1100mm channel to work with under the car, what would be the profile of said channel for maximum downforce. (Drag is not a concern at this stage)

Should it have a convergent/flat/divergent nozzle profile to maximise the CSA close to the ground, or a continuous curve more like an aerofoil profile?