The wing mounts pin to a sturdy chassis mount under the carbon decklid. The wing is mounted as far rearward as NASA rules allowed and below the roofline per NASA rules. The wing is trimmed slightly upward as the air bends downward off the roof and we were trying to reduce separation and to make as little drag as possible. The wing endplates increase wing effectiveness by eliminating spillover at the ends of the airfoil making every bit of it work. A wing can also activate more airflow under the car increasing the effectiveness of a diffuser and other underbody aero.
When the car is at ride height, the rear suspension tucks up and does not mess up the flow to the diffuser as it looks like it might in this picture. This diffuser was made from sheet aluminum with hand tools. A few simple guidelines to make your own diffuser. The safe angle to make a diffuser is 7-10 degrees, any steeper than 10 degrees will result in flow separation from the roof of the diffuser causing it to stall, become turbulent, make drag and lose effectiveness. You can do tricks to keep the flow attached but that’s beyond the scope of this article.
One simple trick we used to keep the flow attached to the diffuser roof is to add vortex generators. since our diffuser is at about the maximum angle before separation normally starts or 10 degrees and we wanted to smooth and straighten the airflow which is a bit turbulent since we don’t have a flat bottom on our car, we have 4 of them, those are the black triangles riveted to the diffuser. You can tell our diffuser works, the dirt that gathers there is in long streaks, not swirls that would indicate turbulent flow. Our diffuser reduces drag as well because the stock bumper hangs down like a parachute, trapping, and pressurizing air. The diffuser stops this from happening by cleaning up the undercar airflow here and makes downforce to boot!
8 comments
You mentioned “racket mounted pins that slide into holes on the support bracket mounted on the frame. ” Any chance you have a part number or example link to go off of? Thanks!
The pins were just something we made.
Ive got A Z32 Race/Street setup. Still using the factory locations for the intercoolers (using US spec bumper). Would it be best to have the air exit out the bottom if front of each wheel or put vents in the wheel wells? Currently I am only using the factory exit out the bottom ( the version without the factory NACA duct).
Rear Diffusers in the back are challenging due to the dual exhaust. At this time I am not interested in a side exhaust. How much would it reduce in performance if you ” poke” the exhaust through or would I be better off making a smaller one that just goes between both exhaust pipes?
Last thought. It’s regarding air flow in the Engine bay. Currently I don’t have any holes in the hood, however I was thinking of taking off the molding that seals the hood near the windshield/wiper area. It would leave a 1″ gap along the entire width of the hood where the air could exit. I am unsure if that would help or hurt.
I would vent in the wheel well or better out the sides in front of the wheels. It is better to blow the exhaust over the top of the diffuser rather than in it. Removing the molding at the rear of the windshield is a bad idea, the base of the windshield is a big high-pressure zone, the flow would back into the engine compartment, the opposite of what you want.
By your comment of the high pressure zone in front of the windshield, would that also mean lifting the hood to vent hot air is a bad idea/ineffective?
Yes, looks cool, works bad. Look at static pressure contour from CFD on Google image search. Pretty obvious, it’s a bad spot to vent. You want to vent in LP zones, gurney flaps, and gills, can prevent flow reversion.
Those strakes on the diffuser are flow conditioners, not VG. The point of them is to reduce spanwise flow. They were heavily used on early swept wing aircraft.
Also, the point of producing a vortex, is to have an effect on a surface downstream, pointless to put VG on the rear, unless that vortex is directly making down force (which is unlikely, but not necessarily inconceivable.)
I disagree and so do other motorsport aero guys including the guy who helps me that has a PHD in fluids.