Yes, i know what a diffuser is and what it allegedly does. Which ones work the way they're supposed to, and how fast do you have to be going for it to have any effect?

Edit: did you notice any other differences after installing it?

 

In a car that weights as much as an FD a good diffuser will only make a perceptable difference at speeds well over 100 MPH.

I could not give you an aproximate downforce figure for an FD that depends on the shape and depth of the diffuser. For reference, on a 1300 lbs Formula Atlantic race car a diffuser tunnel provides 2300 lbs of downforce at 140 MPH. In comparison the front and rear wings an a Formula Mazda race car provides only about 200-400 lbs of downforce.

Albert

Edit: a good clue is that if the diffuser is mounted with some flimsy screws and bolts and it actually remains on the car at speeds over 120 MPH than, it is not very effective. As you may imagine an effective diffuser need to be mounted in a VERY sturdy way.

 

Now is that exclusively the diffuser tunnel or are those figures extrapolated from the total downforce effect of the aerodynamics on the car?

 

Since I only raced Fomula Mazda my information regarding the FA car came from a friend's Crew Chief, for his FA team car. He stated that the tunnel provided 2300 lbs downforce, not inluding the wings and the body.

You notice that the FA cars do not carry all that much wings. They represent a lot of drag, while the diffusers are an almost "free" downforce.

Albert

 

I myself am not a big fan of wings, but i've also noticed that my driving style or my lack of useful tire has made my car tail happy. Even after i get new tires i want to eliminate the problem efficiently at every speed.

 

Very interesting. Thanks for sharing.

 

You are most welcome.

As an interesting side note on the FA tunnels:

The Crew Chief suggested that with the amount of down force that an FA develpops one could drive an FA car on a ceiling, upside down, being sucked to the ceiling and never fall off, as long as you could maintain your 140 MPH speeds.

I ran in the same race group with the FA cars and their cornering speeds and abilites send cold shivers through me. A Formula Mazda goes through a corner far faster than a GT car but, an FA is INSANE. These guys (the top drivers) stayed on full throttle far beyond my FM braking points, they would go through high speed corners without litfing off where I had to brake for the same corner. That downforce does wonders for cornering speeds.

I had actually considered moving my FM to an open FS class and engineer my own downforce tunnels into my car. I chickened out as I did not have access to wind-tunnel testing and simply did not trust my engineering with my life. You can imagine if I made a mistake in supporting the pods and the tunnels broke off during a 140 MPH corner. You'd go off flying and hit so hard that it is just not an attractive thought

Albert

 

The use these so called "diffusers" that people like RE and such sell are pretty much aero useless...

1 the cars ride height is way to high... the closer to the ground the more affective GA become IE. reasons why most sanctioning bodies have minimum RH requirements, most GA cars are run in the 2" to 4" range...I have not seen many fds running this low.

2 the affectiveness of the difusser is highly dependent on the air it is supplied with....the air comming through the bottom of an fd is going to be super turbulant do to all of the dead ended cavities. also most of the bolt on diffussers I have seen are in no way sealed on the leading edge to the bottom of the car which means the air comming across it can go over and under it = negates the whole purpose.

If you were willing to spend the dough and time you could make one functionall but it would require you to..

1. run the car very low and stiff..not bad if this is a dedicated race car but you would probably also have to stiffen the chassis a lot in order to keep it from tearing itself apart

2. fab up a false flat bottom or tunelled floor the whole length of the car.

3. in order to really be able to use its benefits with any kind of success you would really need to spend quite a lot of setup testing in order to build any kind of reference as to its affectiveness.

 

I beleive the only purpose is for stability on turns or so that's what was said on tv. I can't rememver which show it was. Is that not correct? It's used to keep the rear end planted or prevent it from lifting on high speed turns? So drag racers and street cars < 100mph won't have much use for it. There was a clip of a police chase with a corvette doing 120mp (i think that was the speed) and it tired to manuver around a semi when the rear end lifted in the air and smashed in to the semi trailer. Maybe the diffuser would have prevented that?

 

well, don't believe alot of what you here on tv.

Diffuser's,tunnels, skirts... are all forms of ground affects.

ground affects are the use of the bottom of the car in relation to the ground to produce downforce via a ventury created by the shape of the underside of the car and the distance of it from the ground. where this downforce is located in relation to the car is affected by a whole range of factors (rake,tunnel length, diffuser height....) this placement is refered to as the center of pressure. the total amount of downforce is directley related to the velocity of the air moving across the device...you are correct that most street cars will find very little benifit, mainly do to the low speeds and reletively High RH....also the amount of suspension travel incountered makes it almost impossible to maintain any kind of consistant RH.


down force = more weight on tires = more grip....grip doesn't car if the car is trying to turn, slow down or speed up it will benefit everything.

 

I believe having a diffuser on a streetcar wouldn't be very functional. However, 1 can debate if this was true, Ferrari wouldn't go through so much trouble designing the underbody of their cars.

However, I think 1 gets a diffuser to individualize their car. Whether it be from REamiya or from Mazdaspeed themselves. I seriously doubt anyone is thinking of getting any real use out of diffusers for street use.

Race use is different. Lots of factors come into play.

Pointing that out, I believe Mazdaspeed has tested their diffusers and they are functional in smoothing out the airflow under the car. Provides a bit of downforce at the appropiate speed. Which is probably why they cost so much and probably why many people don't have it on their cars.

 

The diffusers have very little practical effect on these cars on the street. Tires, on the other hand, do. Put on better tires and get your alignment adjusted if you think you have a grip problem. Aero won't solve your problem.

Wings and diffusers do the same thing: they trade drag for downforce. The one advantage of a diffuser is that it's at the front of the car, while a wing relies on air to flow over the car body and into it. In turns, the airflow over the wing is much less clean, while a diffuser continues to engage good laminar air. So you'll always trade acceleration and top speed performance for grip when using aero components.

Dave

 

the diffuser might be more functional with a full underbody panel, but without it, its more than likely just for looks.

 

The alignment is fine, i don't have any bump steer issues and it tracks straight as an arrow. The issue is my tires and my broke ***. So here i am asking silly questions so when i do have money i can solve the problem and perhaps make an improvement to my handling characteristics at speeds my car doesn't see terribly often :P

 

New tires are much cheaper than new bodywork. In other words, get some tires before it's too late!


For the budget conscious, look at the Avon Tech M500. You can get them from tirerack.com , and many tire shops are now 'special-order'-ing tires from Tire Rack. I've been using their 245/45R16 tires on stock wheels and suspension for a couple years, and they've got plenty of grip and have worn well also.

-s-

 

if i hadn't had to get body work, i would have money for new tires. mother nature is a *****.