Interesting topic.

I've put a front BRE type spoiler on my 71 Z twice over my 41 years of ownership, only to have them cracked or broken due to "parking errors" on my part.

While this helped the car at speed initially some 30 years ago prior to suspension upgrades, it didn't seem to help much after I lowered the car with new Tokico springs and struts. I have since removed the spoiler (for the last time) and the car seems to track and drive great, have less "crosswind" effect, even at speed.

Go figure.

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John Kish
1971 240Z - original owner

No, that makes perfect sense. By lowering your Z, you have defeated most of the problem. The front spoiler serves to keep air from running under the car and lifting it like an airplane wing, since the air running over the top of the car produces less pressure than the air running under it does.

Aerodynamically speaking, the Z silhouette resembles the edge of an aircraft wing. Driving at speed results in lower pressure on top of the car than under it, which causes lift. That's great if you're trying to fly, but most of us prefer our wheels to remain on the road.

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1970 240Z

Here's an interesting wind tunnel "smoke" test (technically not "smoke", I guess, but I call it that) done on the old SuperBird. I can't find a smoke test on a 240Z anywhere on YouTube.

You can zee how the smoke (dry ice?) tries to hug the upper silhouette of the car when it can, but at 02:45 they demonstrate what happens in the low-pressure area behind the rear window. On the S30 Z carz, that area is the sloping hatch, where the air can't hug the car like it wants to. That results in a low-pressure area with disrupted airflow, which a REAR spoiler tries to restore. On the old 1970 carz, the cabin vents were mounted exactly there, which resulted in exhaust fumes being sucked back into the cabin.

The purpose of the big rear airfoil is to redirect airflow back down onto the car body as much as possible.

If they were able to show a side-shot of a lot more smoke, you would notice the airflow running under the car reaches and leaves the rear bumper much later than the airflow OVER the car. That results in denser air beneath the car than over it, which equates to more air pressure under the car than on top of it. That's what makes airfoils lift planes off the deck, and what makes old Z cars get 'light' in the steering.

By attaching a front chin spoiler, (or by lowering the nose suspension), we reduce the air running under the car. With a full air dam, we eliminate the under-car lift altogether.

http://www.youtube.com/watch?v=s-t5WKkg ... re=related


And here's an example of a slightly modified rear wing, making a remarkable difference in airflow on basically the same kind of car:

http://www.youtube.com/watch?v=7Xc5TjtZ ... ure=fvwrel


Sure would like to zee an old 240 in the smoke test!


Frank

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1970 240Z

Nice smoke show of the Super Bird @ A2. If I remember correctly, A2 was the tunnel that the Hybrid Z 240 was tested in. The use of CO2 aka Dry Ice is a cleaner way of producing “smoke” in limited quantities (It takes a lot of D-Ice to make a worthwhile run). We used a multicolor (dyed) kero based oil mixture (combusted) pumped thru an X-Y-Z multi-tube traverse array. One of the big problems was that it is somewhat dirty and only provides limited aerodynamic information. Although a 5gal bucket would provide hours of HD video, again it was dirty, coating the model, test section and the diffuser section but far worse, it gets into all the instrumentation and balance mechanisms. For an hour smoke show we had to put aside a 2 days of clean-up before resuming “real” testing. As we use to say it was only good for IMPRESSING the Brass and the Public Relations folk. The best flo-vis is tufting and better yet iridescent micro tufting i.e. “the string thing”. Needless to say, in order to assess the effect of the wind, you must be able to first see the tufts and correlate accurately the aero conditions that they are currently subject to. A high end HD/HR Video Cam System with a real time display of tunnel conditions works fine and of course it must be set well away from the test area. Alas this method is also subject to interpretation and speculation. What we are looking for is “boundary layer separation and detachment” that causes turbulence i.e. induced instability/ drag and disrupts the attached “near laminar air flow” over the model. This is decidedly the domain of a very expensive high speed data system, extremely sensitive pressure transducers and a “spider web” of micro-tubing that is coupled to sometimes hundreds of static & total pressure mini taps (0.062”<) that have been strategically located and laboriously installed. Oh ya, last but not least, a whole lot of very smart people willing to sit around for weeks on end, sifting thru reams of empirical data to produce a mathematically accurate aerodynamic profile that is based solely on objective and impartial evidence. Don’t get me wrong……………I like smoke too but I defer to the math.
In the early 90’s I played around (off hours) with a 1/10 scale 240Z (Old R/C car) that I swapped in and out different front & rear spoiler configurations in the UTRC Pilot Wind Tunnel (PWT). This mini tunnel has a 5’ Test Section and Capable of approx. 110mph (MWT its big brother, has a 18 foot test section and capable of 650mph+). PWT was fully instrumented and has a complete compliment of Lift, Drag, Yaw & Side/Down Force Scales. It however does not have a “Rolling Ground Plane” which is somewhat essential for accessing automotive aerodynamics. I wanted to change the rear flairs and spoiler that were on the car when I took ownership. I also wanted to modify the front spoiler which I believe to be the most common aftermarket spoiler available. As you can see I narrowed the existing the rear duck tail by almost 6” total (3” per side) and cut in a center air bleed (also supports the integral deck lifting handle). For the front spoiler I ducted the original (pho) brake cooling ducts TO the front brakes PADS (4 piston Toyota/300z x-drilled & slotted rotors) reducing a little flow (lift) beneath the car. I also added a spliter urethane skirt beneath the existing front spoiler which also reduces the airflow beneath the car and provides a convenient location for the engine oil cooler. The raised L-88 hood dose a wee bit to reduce air press buildup in the engine compartment, allowing air to escape into a low-pressure zone. Lowering the whole car an inch or so probably did the most as far as reducing drag and increasing hi speed stability. However as others have said, its very ezzz to rip the whole thing off on a parking lot speed bump!!! It’s all about compromise, form vs. function and we should just enjoy what we have. Just my 2 cents on the subject………maybe even a buck or two.

Now see? That's what makes sense to me. The rear spoiler has been extended outward (sideways) so it has significant 'ears' out there in the airstream flowing down the sides of the car. That will force pressure across the blade and exert more downforce on the rear of the car than the standard aftermarket spoilers will.

I also LOVE the shark gills on either fender, *IF* they are functional (I'd be really surpriZed if Dave Russell ever put anything on his Z car for visual effect ~ everything I've ever seen him use is purely functional).

The headlamps are covered to eliminate the air-catching 'sugar scoops', the chin spoiler is low to reduce under-car airflow and uses the high-pressure area to duct cooling air back to the front brakes.

Those "shark gill" fender vents and "reverse hood scoop" hark back to a previous post (which I can't find now) wherein we discussed releasing under hood air pressure. We showed examples of many world-class sportscars which provided vents to release the under hood air pressure. To 150mph oncoming air, this Z would look temptingly 'slippery'.

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1970 240Z