I'm sure this has been discussed before, but I haven't seen any good threads on this in quite a while, so I decided to start this one...

Anyway, I was clicking around on jalopnik.com and I found this thread, Under-Body Aerodynamics Ain't Just For Looking Awesome.


(Pictured above: Password JDM Honda S2000 Carbon Fiber Under-body)

Since most of us spend a fairly good amount of time under our cars, I'm sure we're all familiar with the underside of the body - not exactly the best aerodynamics, other than a front under tray and some few vented panels. Could this be improved?

Why worry about it? Well there are the performance aspects, such as drag / down force, etc., but also, things like better gas mileage, quieter cabin, etc.

I wanted to see if we could use this thread for discussing options related to the FD's under-body. Some things to address:

• Effects of the stock under-body?
• Other cars that address the under-body aerodynamics?
• Available parts for the FD? (OEM & aftermarket)
• Ideas for developing new products?

I know there are a few rear-diffusers out there, and also a few front under-trays, but I don't know much about parts that address the space inbetween.

Personally, I have a Shine Auto Project replica RE-Amemiya Pro-Diffuser, here are some photos:


But what else is there? Check out this photo, for example. Is there anything like this for our cars? Would our cars benefit from something like this? Why doesn't anyone make one?

Here's some more information that I found, on under-side aerodynamics in general:

Here are some more examples of underbody on some high-end cars (links to pics):
Ferrari Enzo: http://tinyurl.com/ygls55w and:

Mercedes CLK GTR: http://tinyurl.com/ydhwf4q
Nissan R35 Skyline: http://tinyurl.com/ybqfypt
Lotus Elise: http://tinyurl.com/yj5nn23 (!!!)
Porsche Panamera:


Other Interesting undertrays/diffusers (links to pics):
BeatRush Front Undertray (Mitsubishi Evo): http://tinyurl.com/yflds9l and http://tinyurl.com/yjchu9k
BeatRush Front Undertray (Mazda Miata): http://tinyurl.com/yzkewj4 and http://tinyurl.com/yz56lts
Password: JDM* Underbody (Honda S2000): http://tinyurl.com/yazb8sw and http://tinyurl.com/ydtdgbp and http://tinyurl.com/yd5act6 (product link)



I guess I'll start with a known FD3S products list. Here is what I could come up with:

FD3S Front Undertrays / Under Panels: (links to products/photos)
Mazda OEM FD3S Front Under Cover: http://tinyurl.com/yzhjcoh
C-West FD3S Front Under Panel: http://tinyurl.com/992axq
C-West FD3s Front Under Panel 2: http://tinyurl.com/yhyruww
Jun Auto Universal-Type Front Diffuser: http://tinyurl.com/yzadabd
R-Magic FD3S Venturi Front Under Panel (Type Basic): http://tinyurl.com/yfv5yg7
R-Magic FD3s Venturi Front Under Panel (Type F / Type R): http://tinyurl.com/yjmyqpe
Re-Amemiya Under Sweep: http://tinyurl.com/yh94low
Re-Amemiya Under Sweep for AD Facer-9 & N1-05: http://tinyurl.com/ygulbaj
Shine Auto Project FD3S 3-Piece Adjustable Front Undertray: http://tinyurl.com/ykwjrjm
Shine Auto Project FD3S/Universal 1-Piece Front Undertray: http://tinyurl.com/yz7hfwz


FD3S Main/Body Under-Panels:
UNKNOWN

FD3S Rear Diffusers: (links to products/photos)
Abflug FD3S Splendid Diffuser: http://tinyurl.com/yfcx547
DAMD FD3S Rear Flat Bottom Diffuser: http://tinyurl.com/yhg9r24
EUROU FD3S Rear Diffuser Type 3: http://tinyurl.com/cbgw4v
EUROU FD3S Rear Diffuser Type 4: http://tinyurl.com/yzur4sx
Re-Amemiya FD3S Diffuser: http://tinyurl.com/yfj9st7
Re-Amemiya FD3S Diffuser-Pro Carbon: http://tinyurl.com/yfy5ns3
Sanai Works FD3S Rear Up Sweep Diffuser: http://tinyurl.com/yf6fq49
Uras FD3S Type-GT Rear Bumper & Diffuser Set: http://tinyurl.com/yjd9p8y
Shine Auto Project FD3S Spec-RE (Re-Amemiya Replica) Pro Diffuser: http://tinyurl.com/ykqjw28
Shine Auto Project FD3S Spec-RE (Re-Amemiya Replica) Street Diffuser: http://tinyurl.com/yjmfg3w
Vorschlag Design FD3S Rear Bumper Spoiler with Diffuser: http://tinyurl.com/yls2uce



Share your thoughts, photos, diagrams, etc.

Cheers!
Tom

 

I have not seen a full undertray for the FD... that I can remember. Interesting concept. I wonder how effective an undertray could be made to be as far as downforce, and heat evacuation would be concerned.

 

Relevant autospeed articles

Undertrays (we know these work, but still a good read)

Another undertray prototype

Underbody aero

 

Can someone adapt this to fit the FD?

 

that's actually very similar to the Re-Amemiya "Street" diffuser. Here is the link to the Shine replica:

http://www.forum.shineautoproject.co...read.php?t=133

What I really want to know is if anyone makes, or has custom made a full under-body thing, similar to the one for the S2000 (1st pic at the top of the 1st post).

 

thorough thread with good starting points for research, but no intrest...

cmon people speak up

 

Stupid question: without testing, how do we know it actually does anything?

 

^ I'm with Dysfnctl85. This goes for a number of aftermarket mods I see. I know they add weight. I'd have to be convinced they add much else.

In the case of a full undertray, it's likely it would only help enough to make a substantial difference at very high speed. And then you have to worry about trapping in all that heat from the cat and the exhaust.
A Ferrari with a full undertray has been designed that way from the get-go. All manner of little effects have been taken into account. Not so with an aftermarket part you tack on to an existing design.

And who's to say that a full undertray on an FD wouldn't have an effect that might alter the airflow balance over and around the top and sides of the car? You'd only know that with extensive wind tunnel testing. You're playing with an existing design that has been finely tuned as it is.

But some people can't resist the urge to tinker---even if it has a detrimental effect.

 

an "existing design" that was designed almost 20 years ago.

i'm guessing you have a stock seq-turbo FD all the stock parts, stock wheels, and no mods? or have you been tinkering? how do you think people figured out which mods were worth doing? what's wrong with experimenting and brainstorming?

 

I'm not trying to be an ***, but I believe the reason why this stuff (functional aero) doesn't exist for *many* cars is simply because testing is prohibitively expensive. It's most certainly easier to make a product that looks good and can be sold to the masses under the perception that it provides some sort of benefit. Just look at how many people spend money on pieces wrapped in carbon fiber.

I don't think it's too much of a stretch to say that the same principal applies to aerodynamics parts developed outside of a racing program of some sort.

It's easy to test water injection, spark plugs, air filters, exhaust components, etc. because they can all be validated with a dyno sheet. Seriously, how do you validate claimed performance benefits of an aerodynamic part such as a diffuser without actually track testing it or putting it in a wind tunnel?

 

Exactly!

Aerodynamic refinement is a complex science. As to someone's previous comment that the FD is a 20 year old design, Yes it's 20 years old, but it's a finely honed design with a lot of wind tunnel time.

When you put on a complete undertray you're smoothing out and speeding up the airflow under the car. This airflow meets the air coming from the top and sides of the car at the back of the vehicle. With an undertray you're changing the equation of a finely honed aerodynamic design.

Is it an improvement? Maybe, maybe not. You won't know without extensive aerodynamic testing. It's entirely possible the speeded up under-car airflow is changing the point all the airflows meet, or creating a vortex, or adding to rear end lift, or whatever.

And that still doesn't address the question of added weight. We KNOW you're adding weight to the car. That weight is there ALL the time. So, if you're super-dooper cool lookin' undertray gives you some incremental advantage over say, 100 mph or 120 mph, is that worth the price you pay in the 0 - 60 or 0- 80 range where you do 99% of your driving?

Like some of the stuff around, it's a case of "If it looks cool, do it ----- the actual performance consequenses be damned."

 

Come on bro, you're talking about two completely different types of cars here.
While I really love the FD, it doesn't hold much to the super cars in terms of technology platform. However, keep in mind that those were circa '92 technology so most of the cars built around that time were lacking compared to current-day cars (personally, i would like to see Mazda re-create the FD3S with current-day brains).

If you wanted to be a stickler about this - I recall a F1 team who was whipping *** in a black car with secret aerodynamic tricks in the mid-late 70's;
The other teams couldn't understand what was going on, from where did they achieve this extra power? .... ta ta daaa!! aerodynamics.

My point is, leave the high end / super cars out of the picture.

 

I think that discussing supercars is relevant here specifically because they are designed with underbody aero from the factory.

I do not believe Mazda exhaustively tested the aerodynamics of the car to the extent which race cars are currently tested because specifically because the FD was not a race car. That being said, I do not believe one can slap together an underbody aerodynamics package in their garage and market it as a performance-enhancing system. I believe it's a supremely expensive endeavor and that's mainly the reason why such systems -- functional aerodynamics -- do not exist (at least not to my knowledge) for most cars including FDs.

As for the Lotus you're referring to, it's probably in this generation of F1 cars. Wikipedia says Lotus produced the first monocoque in F1 during the 70s.

 

It's difficult to make sense of your post.

The principles of aerodynamics and design apply whether the car is a Ferrari or a
Mazda.

In the case of the Ferrari pictured in this thread, it's a fully integrated and tested aerodynamic design. It works.

This thread poses the challenge of adding a full undertray to the existing and proven aerodynamic design of the RX-7 (which is already quite good.)

Well, what is there to prove that this is an improvement? Has cooling been taken into consideration? Is there an proof that this undetray improves peformance?
Even if there is some advantage, is it enough to overcome the added weight?

There is ZERO evidence to prove an imagined full undertray on the FD offers any improvement. Yet, some posters seem offended that anyone would question this conjectured modification. It's completely laughable.

 

The rear diffusers for the fd don't do anything. Without a proper undertray to duct the air to the diffuser the air is just too turbulent for the diffuser to do anything but look badass.

The fd also has the same coefficient of drag as a c6 corvette. That antiquated design is really hurting isn't it This is why I laugh when people hang ridiculous bodykits off their cars for the purpose of "aerodynamics."

A proper undertray probably would be great for race cars. It would be a bitch to work on and would cost a ton of money. I couldn't really see it being valid on the street. Another thing that ground effects requires is for the car to be very low.

 

FWIW,
I believe Atomic Rex has worked up a full underbody for the car... maybe Jon will chime in here.

 

All I've got to say is CANARDS. They obviously make a tremendous difference . I'll never forget the tech-talk the Risi Competizione ALMS team (they run a Ferrari F430) gave this year at the Petit Le Mans. The technical director said something to the effect of "our car has canards, but I have serious doubts about whether or not they do anything beyond looking cool." After which the crowd erupted in laughter.

I do think that the C6 above looks menacing. I'm just more of a go-before-show kind of guy and question whether or not such an investment in aero is beneficial beyond getting looks on the street.

 

And now you've hit on it again Dysfnctnl85: LOOKS.

Let's be honest folks, that's what this and several other mods I can think of are all about. "Hey, look at me! My car is baaaad. It's all racy and s**t."

Some of these body kits....fine. If you want to distinguish your car from others, more power to ya. But don't tell me you did it to enhance performance. At the speed you're really driving that thing all you've done is add weight and aerodynamic drag.

The FD, as it was designed, still has a very good coefficient of drag, and from all the reports I've heard, it's stable throughout its speed range. That's the stuff that counts.

 

Man I love Jalopnik!

I believe someone on the forums was working on a full body undertray just nothing has come out of it so far. I imagine the undertray would get scratched up alot for those slammed or lowered cars. I know sometimes the bottom of my car hits and my car is only slightly lowered.

 

I will be developing aerodynamic components for our FD.

I have a degree in aerospace engineering and also have military training on helicopter blade construction and reconstruction. When I am done with my engine, I will be developing the following:

Rear diffuser similar to Kenstyle and Sorcery for the NSX
pop-up headlights with intake port and projector HID's
full front undertray
front bumper rebar
underbody components ultilyzing stock mounting points such as where the seat bolts onto
full lightweight dash, door panels and center console
front fenders

Hopefully, by the summer I will have some stuff to show...

 

Hiya Guys....Time for me to chime in

We do do a full underbody system. Marco texted me to say this thread was up and running, but just for once I'm not at the workshop late in the evening...so I don't have any photos with me.

The system includes:
Carbon Front Splitter
2 Carbon flat floor sections
Carbon Diffuser
2 Side Skirts

To compliment the diffuser, we use a centre exhaust system, which exits within the centre tunnel. The whole system is raked by 10mm, so there is a slight height differential between front and rear, but is designed to run with a 50-60mm ground clearance.

We are going to be running the system on two different cars, our standard track, and the wide body. The flat floor protrudes out either side, and to fill the gap this is done via a side skirt.

As said I will get some pictures of the kit up on Monday

 

It's a very clear post I thought. I'll touch on my thoughts again in short:

Mazda clearly had the funds to provide the car with a full under tray but did not. Much like they did not provide the FD3S with better quality twin turbos.
However, a friend of mine did manage to talk privately with one of the Mazda Employee's who was part of the chassis design team for the FD3S and the short end of that conversation was "Economy was good for us in those days - we did not need to watch budget" as he recalled. With that being said, I'm very sure the dynamics of the underside of the car are just fine, however, I do not think it can be compared to a factory like Ferrari. This is a company who measures the thickness of the paint on their cars as part of quality inspection. I'm not saying Mazda is cheap - only implying they most likely do not go to that extreme for their mass-produced autos.

Again, I'm not disagreeing with anything expect showing a photo of a high end car with unmeasurable amount of research and design and comparing it to a 1993 Mazda car built for mass production and distribution. Even with that out of the way - compare a 1993 Porsche 993 or '93 Ferrari 348.. I think your dynamics tests would be equal comparison(read: not a late model super car vs. 15 year old car).

On another note - I would not want to enlist the help of an aid when i needed access to he bottom side of my car. Removing a full body undertray would be a pain. In a modular / sectional design it probably wouldn't be so bad.

 

My 2cents it that you are just wasting your time and money until you ensure that all air entering the front of the car exits on the top or sides rather than underneath.

Here's a link someone who built their own undertray for another car for a reason other than downforce.
http://picasaweb.google.com/threewhe...oothingPanels#

 

I posted an autospeed article about a 1/2 center undertray that was fabricated out of sign material here. It was fabricated in 3 hours, it did not show any improvement beyond standard deviation. However, the potential *is* there for someone to go farther.

Saying that the vintage 1992 design is perfect is not correct in the least. If it was, we wouldn't have to do reliability mods, because the system would have been "exhaustively tested" just like the aero.

See also: The Amemiya Genki 7

 

Interesting thread.

It shouldn't be too difficult to quantify changes in aerodynamic drag by doing coast-down testing. Google it, you basically put the car in neutral and record vehicle speed vs time: lots of drag will slow the car quickly. Should be a pretty simple test if you've got an aftermarket ECU that can datalog vehicle speed. Slightly less easy would be to use a camcorder (or digital camera or fancy cell phone in movie mode) pointed at the speedometer.

Someone on these forums once claimed that removing the front fender liners improved their 3rd or 4th gear acceleration times by a significant margin.



Unfortunately measuring actual downforce isn't nearly as easy... the best most of us can do may be to infer 'more grip' or 'less grip' from very controlled testing. If you've got some way of measuring actual cornering g's that's a step closer. If you've got a lot of resources you might be able to measure suspension travel... find a straightaway and compare ride height with and without aero. You might take this a step further and compare those numbers against ride height with ballast.

Don't forget the weight of fuel if you're testing over an extended period of time... a 5-gallon fuel jug is pretty heavy when full.