Riccardo

iTrader: (1)

Any pics of Mazdaspeed rear diffuser other than these two...I have searched extensively but no luck
I am considering putting the one that fits on the stock bumper but would like more detailed pictures to see what it looks like

peterh

http://www.fd3s.net/diffuser/index.html -> try here.

Riccardo

iTrader: (1)

many thanks but it is the same picture

afgmoto1978

iTrader: (6)

http://www.japanparts.com/db/partsli...dle=2&small=11

Riccardo

iTrader: (1)

Many thanks
Any other pictures ?

Riccardo

iTrader: (1)

I don not understand how no one on the forum has really purchased this item

TRISPEEDFD3S

iTrader: (26)

It's really expensive, and the RE Amemiya and Sanai diffusers look better.

95MX6

Because it has a limited effect on a street car due to a several factors.

1. Ride hieght has a large impact and most street cars are a not low enough/stiff enough.
2. Without underbody panels to smooth air flow the effect of a rear diffuser is somewhat limited.
3. Limited effect at speeds below 100mph.

If you are willing to address these issues then a rear diffuser can create a large amount of downforce at speed (100+ mph). For example the majority of a Forumla 1's downforce is from groundeffects (which the rear diffuser is a major component of), the large front and rear wings provide less than half of the cars overall downforce.

It's just not a cost effective way of decreasing lap times for most of the people on the forums and serves no real function on the street.

TRISPEEDFD3S

iTrader: (26)

They look nice to have! HAHA!

Neo

iTrader: (3)

I've been wondering the same thing for awhile now.
I'm only getting these pieces because my front tray is mangled and the rear plastic trim on my bumper has melted.
I figured it would add a nice personal touch to the car.

7racer

I ordered the one on the yellow car from Fdnewbie...

hopefully it will be here SOON!

Riccardo

iTrader: (1)

95MX6 you are right regrading the aero, however I would say less than 100 mph - I am also studying maiking an underbody panel from the seats backwards...any issues on heat ?

However a great number of people have been using the Amemiya & Sanai diffusers, which are equally priced for me in Greece

7racer, please post pics when you get it

Neo

iTrader: (3)

7racer,

I've emailed and PM'd Fdnewbie, but I haven't gotten a response? Is he on vacation or something?

I'm definitely getting the rear and front diffusers and I was hoping to get it from him.... but I can't seem to find him...

TRISPEEDFD3S

iTrader: (26)

See, I'm going to get the knock off ones from shine auto here in the states. It will be extremely cheaper. It's just a looks thing for me anyway.

FDNewbie

iTrader: (10)

Yea I know I know...you don't have to remind me :runs and hides: I think you'll be happy to know that I sent in the paperwork for the shipment yesterday

Sorry...yes I was out of the country over a few weeks. Even businesses need a breather once in a while... I'm slowly but surely responding to the ton of inquiries that came in right around the holidays; I'm sure you'll have your response soon

Thanks,
~Ramy

Neo

iTrader: (3)

Woohoo! FDNewbie lives!

FDNewbie

iTrader: (10)

Even better...check your email

kuroi FD

Why dont we get enough interest to get shine to do one of these? I think people would rather have this than the RE or sanai one. Comments?

FDNewbie

iTrader: (10)

I can tell you this...if the very few ppl who are interested in ordering this currently find out it's going to be replicated, they'll probably lose all interest in the piece. You see, one of the main reasons these are sought after (other than the high quality and aerodynamic testing behind all Mazdaspeed parts) is that they're RARE

~Ramy

95MX6

The FD actually has very little lift for a production car.

Baseline RX-7 RX-7 R2(R1)
Cd, drag coeff. 0.29 0.31
Clf, lift coeff FRONT 0.16 0.10
Clf, lift coeff REAR 0.08 0.08

This is a good book to read on the subject of car aerodynamics.


The equation for lift is .

where:

CL is the coefficient of lift
ρ is the density of air (1.225 kg/m3 at sea level)*
V is the freestream velocity, that is the airspeed far from the lifting surface
A is the surface area of the lifting surface
L is the lift force produced


As you can see the velocity or speed is squared, so the lift at 100mph is 4 times that at 50mph. Without knowing the lift surface area of an RX7 we can't accurately calculate the exact lift at any given speed but an aproximate number would be 400lbs of front lift and 200lbs of rear lift at 100mph vs 100lbs of front lift and 50lbs of rear lift at 50mph (using Baseline RX7 numbers from above). At 50mph the effect of losing 150lbs of effective weight on the tires (of the 2800lbs) is minimal. Even changing the lift to -0.1 (downforce) for both front and rear would only generate ~130lbs @ 50mph. Please remember these are aproximations, even with an accurate surface area (which I don't know) the only 100% accurate way to measure lift is in a wind tunnel with scales measuring the weight on each wheel.

That's why I state 100mph+ is important for aerodynamic parts on a car. Most production type race cars aim for a 0 lift coefficient. Without major changes to the shape of a production car it's hard to generate any real downforce. Formula style race cars are function over form and can generate huge amounts of downforce (F1 cars I believe generate 2+ tons at 200mph).

It's also important to balance the lift/downforce front to rear, too much lift in the front with very little in the rear could lead to this RX7 crash at 215mph.


Of course none of this applies if you are just adding a diffuser for styling reasons. I don't want to scare anyone off, adding a diffuser for styling is fine just don't expect to stick to the pavement like a F1 car by adding a single body piece.

FDNewbie

iTrader: (10)

95MX6, here are a few #s to add to your calculations

From Mazda:

- The coefficient of lift for the front of the FD (R1/R2) is 0.10 and for the rear is 0.08 (In contrast, the estimated coefficient of lift for the 1995 Ferrari F355 is -0.24; ie it actually generates DOWNFORCE).

- The FD's aero numbers are 19.26 sq ft frontal area and .29 drag. That factors to 5.585 (for comparison purposes to say, the 2005 C6 Corvette, which factors to 6.132).

- "Developed specificially for the 1999+ FD3S, this is the fully functional genuine OEM 1999+ rear wing. This updated rear wing was made to meet the critical role aerodynamics play in the FD3S' peformance, given its light weight. The wing features and adjustable-rake rear center blade with four alternate angles to create varying amounts of downforce while providing a spoiling effect to reduce drag. The 4 positions for the center blade are at 1, 5, 10 and 14.5 degrees. At the standard one-degree rake, the front lift coefficient is 0.045 and the rear 0.000. At the extreme fourth setting of 14.5 degrees, the car generates a front lift coefficient of 0.053 and a negative rear lift coefficient of -0.075, pushing the rear end firmer onto the road surface."

Neo

iTrader: (3)

The F355 was designed initially with downforce in mind. Not as much as it's successors, but some. The whole downforce hype started with the new 360.

It's still stunning to see a 13yr old car outperform some of the heavy weights being offered today. The FD was designed and engineered way ahead of it's time.

95MX6

I was at work when I posted so I didn't have my books on hand.

"RX-7" by Jack K. Yamaguchi and John Dinkel states the RX-7 has a front lift coefficent of 0.04 and a rear lift coefficient of 0.01.

"Race Car Aerodynamics: Designing for speed" by Joseph Katz states...

Baseline RX-7
front lift coefficient 0.18
rear lift coefficient 0.08

RX-7 R2
front lift coefficient 0.10
rear lift coefficient 0.08

Not sure which are more accurate.

Unfortuately frontal area is only useful for calculating drag, for lift you need the total area of the top half of the car. Since cars can be viewed as a wing and the upper surface of a wing is the "lifting surface".

But Joseph Katz goes on to say (starting at page 252) that production cars can be modified to generate a large amount of downforce, the 1991 IMSA GTO RX-7 used a rear diffuser, an aggressive rear wing (aggressive in angle not size), and a low ride height (and some other tricks) to generate -0.3 to -0.4 lift coefficient. That's a lot of downforce at 150mph, of course a street car would have to have some stiff sprints to avoid making contact with the pavement with 1000lbs+ downforce.

From what Mazda/Mazdaspeed has to say about thier 99+ wing it sounds impressive (and always has), if quicker lap times are your goal it's hard to go wrong with that wing on the forth setting.

Monkman33

iTrader: (28)

that wing on the fourth setting will make high speed cornering a bit of a tussle though. it is all about balance of downforce in respect to average speed over the course.

ultmtrx8

iam with you on that