348 Rear Diffusers - anyone seen any?

Unless ya fit the complete undertray to match the diffusers they would not be any good by them selfs. The flat undertray/Ground FX channels the air to and through the diffusers. This causes low pressure under the car thus adding down force. This on a 355 was not just thrown together, it was designed in a wind tunnel to add pressure to the rear of the car instead of using large on boot spoilers.
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Thats about right too chaa.

 

It would seem to me that some of the ground effect on the 355 is seriously disrupted by the hole in the undertray at the engine sump. IMHO, although the the 355 diffusers do have some aero effect, it's mostly for look. The 348 does have a full belly pan up to the front of the engine, but without the V- shaped stepped tunnels of the 355.

The diffuser kick-up accelerates the air as it exits from under the car and the strakes keep air of different pressures from mixing.

 

Point noted ...

Here is a 348 underbody for comparison. Looks like 60-80% of the 355 undertray is installed.
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I suppose it would not be overly hard to incorporate some 355 diffusers on the 348. Just make some brackets ect....
They would never work 100%, but would still look the part.

 

The aerodynamic effect of the rear diffuser is to accelerate the air underneath the rear of the car. As the air accelerates relative to the air on top it creats a negative pressure, ie Barnuli's (sp) prinicple. This adds down force.

I don't think the diffuser on the 355 creats enough air flow to get any significant down force. Not that it would really matter at normal road speeds. Maybe the 360. That's why the 355 CH uses a rear wing and the 360 and 430 CH's do not.

It looks cool especially in carbon fiber.

 

Actually these dumb things can have quite an effect. Homebrewing splitters, wings, and diffusers is easy and have significant benefit. For laughs and giggles I tried a large NACA profile wing about 10" x 6ft I think and on the track I am 10mph faster in the fastest stretchs with much greater stability which gives the chicken driver the confidence to go faster. My spiltter and diffuser will go on at the same time. My problem is that the splitter is a full 4 1/2" carbon splitter and I can't get the car on the trailer because it is so low. So I need to find another way to make the splitter removable. Easy in concept a pita in practice. If you look at 360 and 430 bottoms they are flat with some defined areas like the 348. The 355 is the only undertray that "looks" developed because of the funky middle section etc. I forget the downforce at 120 was like 150lbs on the 355. I am not sure the downforce is as significant as the fact that all cars produce lift at speed they are wings. So if you get 150 lbs down that is huge! Ride height and consistent ride height is critical to the function of splitters and undertrays. I don't think street suspensions benefit from these other than looks. But a properly set-up racecar will be paid dividends. Based on what the 360 and 430 bottoms look like I bet the 348 with a rear difusser is 90% of what the 355 with all the gadgets could do. Also realize that a rear diffuser could be made much larger in the 348/355 that the oem diffusers which were really slit trays to channel air. You could easily make a 360/430 ish diffuser for the 348 which would be as wide as the measure from exhaust opening to exhaust opening. The surface area here will be much bigger than the 355. Remember that the 355 was a first generation of not only road car aero but F1 gearboxes. Ferrari has learned so much more since then on both fronts. So It does not take too much for a stooge to copy the new technology even if we lack wind tunnels. Old Billybob will report his results here around october'07 with laptimes...a cheap windtunnel if you will.

 

Seems to be a few arm chair aerodynamicists on here. Using expert phrases like, "it looks like" and "it seems like" LOL! so ferrari got it all wrong ey The 120-150lbs of down force isn't really there ey? The hundreds of hours in the wind tunnel was all wrong ey?
You should really remember that without the 355s basic ground FX, there may not have been the F50 ground FX either which was made a year after the f355s production. And nor any of the other road ferrari ground FXs that we have today like the 360s and F430s. I think that's a good ground breaking legacy for the F355 to be remembered by...isnt it??
MB: The hole in the undertray was designed to cool the underside of the engine via the finns.

 

Also noted dude And it looks that way. Its seems like and early step towards the wind tunnels 355 undertray. The reason the 355 undertray developed into the form it was/is. Is due to the undertray being smooth and flat to allow the air flow to flow uninterrupted. With the 348 underside the area is not smooth but has nooks for the fast flowing air to grab onto thus causing turbulent air. But yes maybe the 348 was the first step. Would be interesting to know.

 

At a speed of 185ish the following ferraris produce the following downforce.
Things have moved on at a great rate, but interesting to see the F50 built at the same time as the 355 with more DF than the F430 and CS. But check out the Enzo!!!!!

Model = lbs = kg
F355 = 220 = 100
360S = 374 = 170
360M = 397 = 180
F430 = 550 = 252 (360 + 40%)
F430 = 573 = 260
CS__ = 592 = 270
F50_ = 683 = 310
Enzo = 1710 = 775

 

Do you mean like these?
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Well these are nice numbers but you probably can't get to those numbers on a typical race track with corners during a race. Maybe a high speed NASCAR oval you can. I have never been on a complete oval. On typical road courses with a couple straights and high speed banked sweeper 120-140ish are likely numbers. I do not think aero downforce is linear. I don't think even a 430C could get to 185mph on the straights of a typical roadcourse. It seems that 150-160 is more likely tops. Has anyone here hit those numbers on say laguna seca or WSIR? I think even the 348 was capable of reported 187 top speed but it take a full day to get it there.

 

Totally agreed, but maybe you should write a letter to ferrari and tell them that There not my figures there ferraris
As for top speed i have had just short of an indicated 180MPH in my 355, so 185 is deffo a no no in one. But i have had an indicated 190+ in both 360 and F430. There were no race tracks involved as i drove from Portugal through Spain and France to the UK

 

Ernie,

Being sans windtunnel armchair aerodynamicist I can only guess at how to do a 348 diffuser. The pix you show are a start. I'm going to cut the bumper center section out between the exhasts tips and the bottom of the license plate. That will open up a large area to blend and direct the airflow. You can see this on the backs of the 360/430. This increases the diffuser eficiency that the original 355 design did not do and takes away some bumper parachute. I'm not sure the 348 designs you have pictured do much as flat extensions of the flat underbody. I have not decided where to route the exhaust. I may even route it out holes in the diffuser also known to improve diffuser action. Regardless of what happens think home made diffusers will do little relative to real splitters and real rear wings. Plugzit uses that dinky 1 1/2" splitter and says he feels a difference. I'm not convinced. I think you need to be in the 3-4" range for those effects at reasonable club race speeds 85-150mph. With only a rear wing now I am amazed at the car's reponse. It was the radical effect of the wing that got me to pony up the bucks to have a carbon fiber splitter custom made.

 

Is the picture Ernie posted your car fatbillybob? Have you used a complete undertray or just the diffusers? Have you noticed a large degree of difference over the standard set up?

 

Read the posts! At normal road speed the diffuser gives little down force. You don't even over come the mechanical down force of weight, friction and gravity under 100mph. At 120 mph as FBB said or in you post at 185ish the under tray produces aerodynamic down force. When was the last time you were driving 185ish, and did you notice the down force effects?

 

Ah....you mean something like this??? http://ferrarichat.com/forum/showpost.php?p=135505386&postcount=8

 

DRT348 The last time i drove at over 180 was only with in this last two weeks, and i dont know what i should have been feeling at that speed. Hey and why ya trying to make a point with me. Take up any figures you have with ferrari, dont shoot the messenger, relax

 

There is in fact an undertray that covers the engine sump on 355.

 

I'm not out to shoot anyone. My point being that few Ferrari owners ever drive 180mph. Few probably reach 100mph and only for very short distances. Will the small rear diffuser (relatively small 120 -150 lbs of down force, considering some race cars have 1000+lbs down force) really conteract the lift created by Bernouli's principle as the air accelerates off the top rear of the car at speeds of 180mph.

 

You have 3000+ lbs of down force (the weight of the car)! The question is at what speed that down force is over come by lift created by the car and how much wing do you need to keep the car on the ground. The more wing the more drag and lower top speeds! Something F1 guys try to balance all the time.

Don't get me wrong, I like the carbon fiber pieces and would consider adding for looks.

 

I don't think this is an issue at all. Ferrari did all this pre-1995 when I did not even know what a diffuser was. But that does not mean this technology is current or the best anymore. Even you have commented I think on the Throttle bodies threads right? Well home made diffusers from armchairs are no different than throttle body swaps that we would never have concieved in 1989. Best part is they work. Plugzit is way over the 348 HP numbers and he is not even dialed in yet. Why can't a home made diffuser blow away what Ferrari did pre-1995? Arm chairs don't know anymore about motors than they do about wings.