What's up everyone? I'm new to this site since about a month ago when I got my '04 GT (Grand Touring) RX-8 and I absolutely love my car. I'm posting this thread to the concerns of the people who want to actually improve the handling/speed characteristics of their RX-8 through modifying the chassis and body. I'm a Aerodynamic Engineer for Bridge Aerodynamic Inc. located in Pittsburgh, PA. I graduated from Duke with a Master in Aerodynamic and Fluid Engineering. Enough of that, let's get this started.

First, if you have a warranty on your RX-8, you may want to check with Mazda if the modifications your'e about to do will not void the warranty. You guys probably know a lot more about the warranty disclaimer and guidelines more than I, I'm just trying to look out for all of you because I know how easy the dealer can screw you over.

Q: Can/will body kits increase the Aerodynamic Efficiency on my car?
A: Yes, but VERY VERY few. The CD (Co-efficient Drag) on our RX-8's is 0.31, which is OK. Usually depending on material of the body kit (Flex strength) and how wide it protrudes from the body itself (the wider, the more wind resistance) and how many (un)necessary holes it has will tell you if it's actually helping with your CD. If the body kit has a snug fit onto your body and is either made out of carbon fiber or Poly-Urethane and doesn't have too many holes, it COULD help the CD and downforce. If you guys want me to explain this part more in-depth, PM me please.

Q: That huge spoiler HAS to give me downforce, right?
A: Depends! If your car is RWD (which all of ours is) and the spoiler is made out of a sturdy but lightweight material, and isn't higher than 3/4 of the back window and is fixed onto the body of the car (which means NOT bolted down), chances are your'e going to get better CD and downforce. But, all of our RX-8's are bolt-on spoilers. Bolt-on spoilers will give you more of a current curve, which is good at high speeds, but none of our cars will go 170+ stock. If you are in a slipstream behind a vehicle going 110 MPH+ and have a bolt-on spoiler, your back end could easily slide out if the steering wheel is turned too fast/hard.

Q: Will lowering my car improve CD?
A: Yes, sort of. It WILL minimize lift at higher speeds, hence increasing downforce. Increasing the downforce pushes the car down onto the pavement/racetrack, allowing higher cornering speed. It will also improve the stability of your car at moderate to high speeds and reduces turbulence when behind an opponent at the track. Also to note that CD varies as the square of speed is de/increased.

Q: I just waxed my car, it'll cut that air like butter now won't it?
A: Not necessarily. Although smooth linear particles increase the CD of any object in motion, it will not effect the handling or speed of your car. It will only make wind noise more unnoticeable by very little.

Q: Just strapped on a front splitter, will this do anything?
A: Sure will. This will make the most improvement to the aerodynamic characteristics on your RX-8. It will not only give you better downforce, CD, stability, but it will also curve the incoming air into your radiator and oil coolers. Not only will it do that, it will also reduce the "slyde" of your front tires (It means you can turn heavy and faster without overheating front tires, for more laps.


That is just a simple guide to understanding a small amount of how aerodynamics work and a little modification tips. I could get way more in-depth (Relationship to velocity, Slipstream, Fluid dynamics through engine coolant jackets/oil motion, noise emission, ETC.) If you guys have any questions please PM me and i'll be sure to get back to you ASAP! Thanks for your time. I will post another fully in-depth thread with charts and graphs, as I will be taking my car into work and will do some research on it. I will be testing different body kits, lips, spoilers, width of different size rims/tires, and bolt-on chassisand/or body modifications. Have a nice day

 

It's always a good thing having people with "higher" knowledge around! Welcome to the club and I'm sure may people will welcome your experience and knowledge.
Good luck with the testing and feel free to search around and collaborate with others with similar experience!

 

Nice to see someone apply their knowledge to something like this instead of having a bunch of uneducated people fight it out here. lol

 

Thank you! Also, if their are any specific parts you guys want me to test please tell me and i'll try as hard as I can to get my hands on the part!

 

this is a very nice thread, potentially.

i say potentially because the few who could follow the physics and math of a technical discussion would perhaps benefit in knowledge, but without very precise modeling, or actual testing of dozens of components the practicality of the thread is likely to go nowhere.

I dont have any high hopes of seeing multiple tests being performed, but will cross fingers for ya just in case.

 

Do you have access to a wind tunnel? That would be very cool

 

Understandable, I agree. I will try my best to get as much parts through endorsers and put them on the RX-8 and conduct thorough test. I have a few parts already, but in order to carry out the full potential of the thread I will be getting as much parts as possible.

 

Yes, we do. Reaches terminal velocity speeds up to 187MPH.

 

Which of the Mazda rear treatments has the lowest CD:
1. No rear spoiler
2. The Euro rear spoiler lip
3. The US rear spoiler
4. The Mazdaspeed rear spoiler
?

 

should focus on body underpanels and removing the windshieldwipers.?
OD

 

Here is a piece of data, before and after on springs, dropped the front about an inch more than the back. Saw a solid 1.0+ mpg increase with the next tank of gas. Car was quieter going down the road as well.

 

...

 

cf trunk lid with integrated lip

 

Underpanels and smoothing out the underbody will improve both the CD and reduce lift. Removing wiper could help TOP speed a little by reduceing drag but its not going to effect lift or downforce, so I personally wouldn't bother. Its just not worth it if you run into rain.

A good aero kit like the mazdaspeed front bumper, sideskirts and rear underspoiler will make some aero improvement. The lower front end and sides (1" plus) reduce the air under the car and the underspoiler helps exhaust the airflow under the car and then eases this high velocity air back to normal velocity air stream which all improce CD and reduce lift/improve DF.

A good spoiler for the rx8 is the APR GTC-200 with gournay flap, but unless you are running a serious front splitter, you wont be able to use an aggressive angle of attack. Are cars usually understeer at high speed and a big rear spoiler will just make that worse. A small wing or lip spoiler won't make downforce on our cars but they can reduce drag. A real spoiler/wing like the gtc-200 will make downforce but at the cost of drag. Its a trade off and you must adjust the wing depending on the track.

I have a custom front splitter, my 2nd design, sorry for the bad cell phone pic. I still need to make it pretty and add 1 more splitter rod to the side to reduce flex. The splitter alone improved my lap times by 2+ seconds on a 3 mile course. Grip improved at speeds over 50MPH, and huge improvements at 100MPH+. Splitters make good downforce if properly deisgned and attached to the frame, not the bumper. Best part is that they have almost no increase in drag.

Lastly the air pressure under the hood needs to be releaved. It can be done by a vented hood but improving the airflow under the engine helps too. I have both a vented hood and the beatrush engine underpanel.

Aero mods are trade offs. Most add weight, some add drag and the can effect clearance when driving on the street. My splitter can be easily removed and I swap my wing to the mazdaspeed for the street.

 

Nice work! Love the front splitter. I noticed you picked up on covering the exposed tire surface area. Would you be willing to sell a couple? I'd be interested for track days.

What did the beatrush underpanel do to reduce your underhood pressure? I think many folks who run turbo setups would be keen to know as they are constantly fighting cooling issues and this would help improve radiator efficiency.

Two other pieces I'm interested to get your opinion on.

1) Vorticies Generator shapes and location to reduce drag and improve efficiency of the rear wing.
2) Effective design of rear underbody diffuser to reduce the low pressure area behind the vehicle to reduce overall drag and improve highway gas mileage and rear downforce in high speed corners. 120+ turn 1 at Pacific Raceways.

 

I'm very intrigued by this thread. Has anyone tried running full length or half length venturis? I could be wrong, but i've been told that lift (in this case downforce) ALWAYS comes at the cost of drag...at least when it comes to airfoils that is. Does anyone know how long you have to make the diffuser to smoothly re-integrate the airflow underneath the car back into the airstream?

 

The guys over at RX7club could use a little help

http://www.rx7club.com/showthread.ph...t=aerodynamics

 

The reason a splitter has almost no effect on drag is that it works by building a pocket of air pressure on top of it self and it uses the air that would other wise flow under or around the car. Not sure if I am explaining this well or not. Basically the drag is caused when the air flows against the bumper, the splitter is just taking the drag and turning it into downforce.

Building downforce with a wing will increase drag, however reducing lift and creating low air presure under the car will reduce lift and allow the higher airpressure above the vehicle to produce down force. In extreme cases, vacuum can be made under the vehicle to produce downforce and that will have some increase in drag.

The length of the diffuser to be functional varies, but it does not have to be long. The angle is the big factor and again, it varies. I have a book that gives general guidlines and if I remember correctly, the angle needs to be between 5-30 degress.

Oh a diffuser can reduce drag by preventing vacuum pulling on the rear of the car.

 

Interesting thread. I believe in the past people have said the mazdaspeed wing gives a bit of down force but it is a bolt on. Since its a bolt on, does that mean its no good ?

 

The reason a bolt on wing usually doesn't do much is because it's attached to the trunk lid which flexes. However the bolt location is at the extreme edge of the trunk lid which is adjacent to the latches and directly above a solid piece of the body. If you push down on the brakets, the truck moves a hair with little pressure and then it's solid and you will begin to push against the suspension. So imho, a bolt on still works if the wing it self works. The mazdaspeed wing is not super ridged so it won't make much df, but it does add a little.

Most importantly, without a front splitter, a big rear wing will only hurt the balance.

 

Thanks for the info!

 

Suggested read to anyone interested in this stuff.
Competition Car Aearodynamics by Simon McBeath http://www.amazon.com/Competition-Ca.../dp/1844252302

I have read bits and pieces of the book and use it as a reference. It covers about everything and gives you a good grasp on how things work and how you can apply race technology to your own car.

This next one I have not read but it should be just as good.
Race Car Aerodynamics: Designing for Speed http://www.amazon.com/gp/product/083...XPN14FN3Z3D3KC

 

This is what I am most interested in. I suspect there is improved highway gas mileage, top speed, and mid-speed acceleration benefits to be had from a well design diffuser.

 

The mazdaspeed rear underspoiler/rear diffuser does work. But looks silly without the sideskirts and front bumper.

Your not going to get noticible gains in MPG until you reach speeds above 80-100MPH at which point MPG go out the door.

IMHO, Underbody panels will make a bigger improvement.

 

longpath, The MazdaSpeed spoiler HAS proven to add downforce but by very little. I'm not too sure about the other ones, I will look it up and do some equations for you on the CD values.

Oldragger, I would say to keep the wipers on if it's your DD, but if your'e at the track alot I would gladly recommend to take those boys off! Improves CD by I think around .0093 on any car. Plus, no more flapping at 140+.

04Green, Notice the smoothness? If you want, I could write a paragraph or two about saving fuel and/or reducing road noise with simple, yet adequate driving techniques and just a few mods.

Chad D, that would be very helpful for your aerodynamic properties

Highway8, couldn't agree with you more! PM me, please.


This week I will be taking in my car and doing research on the effects of relative humidity, temperature, elevation and integrated degree of slope on different types of road surfaces related to the STOCK series 1 RX-8 speed and handling aerodynamic properties and how it affects the car. I should have all info and research results Friday afternoon.