Ok, at least one more unknown path to go (?)...
Has anyone tried to make a diffusor that might actually work?

Here are my views:
# don't want a boot wing, spoils the looks/view.
# there seems to be half a diffusor already - without the vertical walls and with an edge of the bumper that's spoiling the flow.
# You never know - it might even work, a little anyway...

I'll make a try and post some pics.

I think you'd need at least a couple of hours in a wind tunnel to produce anything other than a stylish, but pointless looking modification.

I've thought about it - you should really look at replacing the rear undertray in the same job to be honest then it might actually work. I've read in a few places it should not be more than 20-30 degrees.
The best starting point might be the zender rear apron - cut the middle of it out and then bond on a fibreglass diffuser.

Yea, been thinking about taking if off, it's a bit in the way.
Also as you say, cutting just a little in the lowest lip of the bumper may be required, but I stick to my std. one.. Think it'll look ok.

I thought about this too per, but removing the tank and spare wheel well was the route I would take on this - bit extreme for a road car. But it would help to panel the entire underside of the car. Without a chassis lift this would be a slow cardboard trial fit thing. Give it a go.

rich

Does anyone else read 'Practical Performance Car' they are doing an article on aerodynamics at the moment, basically they said, manufacturers spend millions on developing cars in wind tunnels, all these bolt on body kits, wings, spoilers, etc just ruin the car, make it slower and spoil the handling.

Stick with the factory kits, they are designed to work on the car.

true to a point. But my money would be on Fiat not spending a great deal of time in the wind tunnelon the LE kit or on the Fiat/Zender kit.

John

me thinks you'd get one hell of alot more benefit from a
spoiler on the boot.

You won't get any benefit from a boot mounted spoiler, unless it's a proper wing IMO... and then you can't open the boot without sticking it through the rear window.

There are a few different types of spoiler for the rear end, the ones like you see on the rear of a Jaguar where its just a little lip, these are designed so the rear of the car can be shorter but have the same aero dynamic effect as a longer boot.
You get the Subaru style rear wings that believe it or not are actually designed in a wind tunnel, the later ones with bent down tips to the wing are designed the same as those little winglets you see on passenger planes, they stop the lift slipping off the wing so make it more efficient.

The rear end of the coupe was redesigned to give it that cut off rear look to aid aero dynamics, have a look at http://www.fiatcoupehistory.com/e_index.htm for some design info.

The under side of coupe would probably benefit from some work to make it as flat as possible so for those that removed the undertray, it might be worth having a rethink ?

What interests me from the webpage is the early sketch of the coupe (showing two fronts of the car) both have a front bumper very similar to the one Mariusz is currently finishing work on (the PIU remake). This makes me want it even more

RE: The clio not having a functional Diffusor, I read in EVO that it gives 45KG of downforce at speeds over 100, so it definetly does work!

Exactly Suba, thats why we should all be fitting those huge wail tail spoilers to the bonnet !

The trick with a diffuser I believe is that it doesnt increase drag, so it is in effect downforce for free, and also its about minimising lift rather than actual down force , so it can help a fwd car on fast turns.

(The profile of most cars create lift at speed, this is why the audi TT had to be recalled to have a spoiler fitted, crashes at high speed were attributed to lift at the rear )

that is a nice looking bumper, are you going to be making them as well soon Mariusz?

Yas mate.. no exactly Fiat Centro Stile project, but similar.. anyway Chris Bangle designed first PIU style front bumper for Coupe

free diffuser included?

when the coupe was designed (some 13 odd years ago) , was
the use of windtunnels prevalent ?

the front bonnet profile of the Coupe provides all the front
end downforce the cars needs at speed. Its the bit after the
top of the rear windscreen to the tip of the boot which is
devoid of any aero aid for downforce at the rear.

I remember when my coupe was standard (with stock
suspension) , there was noticeable 'float' at high speeds,
eg. at 140 mph. People have been able to reduce this with
lowering the car.

It would be interesting to hear from someone who has
actually installed a boot spoiler and run the car fast.
If not, its all supposition.

cheers.
.

They've been using wind tunnels to design cars for 20 years IIRC.

Pistole,
Lowering a car will help greatly in reducing lift, if you can reduce the amount of air traveling under the car then you will prevent the high pressure that creates lift.

Cars in general and especially the coupe shape are probably very poor for down force, the long bonnet and sloping roof is a similar shape to a wing.
Air takes longer to travel over the roof line of the car as it does the under side, this causes a low pressure above the car and a high pressure below it so you get lift

Splitters as fitted to the front of touring cars, etc can reduce airflow under the car especially when its sitting so low to the ground but I cant see a splitter looking very good on the front of a coupe !

If you look at the std front bumper you'll notice an interesting shape on the sides. That actually helps prevent lift at high speeds at the front. That's why when people fitted the 360 front bumper that doesn't have the same shape they suddenly found the car started to lift at around 100mph. The LE bumper probably does a better job of preventing lift I would've thought? as the splitters probably do some good
I've got the cadamuro front splitter. Whilst it was clearly designed for show rather than go I think it works quite well, and having done near 180mph in my car I still don't get any lift at the frontand my car feels well planted. At the rear it is a bit of a different story I think as the rear does get a bit light at high speeds.

If you drive a lot in the rain on high speed roads you'll notice that the rain doesn't touch the car [much] beyond the end of the roof - that might mean that even if you do fit a boot spoiler that it might not do a lot as its not in direct line with the majority of the air. one solution to that (if you really want a boot spoiler) is to fit a vortex generator on the top of the rear screen. But I would personally rather use a rear diffuser

Have a look out of the back window in the rain John and check out the spray, the coupe makes quite good vortex's from each side of the rear arch but not like you say over the boot lip.
Those vortex generators as fitted to the roof of the mitsi EVO (the one with the carbon lightweight roof) look bloomin horrible, it would ruin the lines of the coupe

Ok, I promised I would give it a shot...

Here's how I did basically, cut cardboard bits til they fitted, then copied them to a plastic sheet:

http://www.garaget.org/?car=1476&image=274681

With a warm air pistol I managed to bend some 90deg mounting points to screw into the rear undertray. Although the front end of the right vertical wing had to be hot-glued to the tank (can be pealed off in case).

http://www.garaget.org/?car=1476&image=274682

As you can see the lowest bit of the bumper is cut to enhance the flow further.
Unfortunately I only found some transparent plastics, I'll have to find something black. Or paint it.

did you track with that?
any difference?

Cool per, that's very nice, me want too. make som to me this sunday?

Yiannis:
No not yet, will do some trackdays next week though.
But this thing is quite unproffesional so I don't expect it to make any huge difference..

Just the thought of it adding 5kg's of downforce at 160km/h is enough for me. On the track, every little thing counts..
According to my "aero-workmate" here at Volvo a really good diffusor would only make about 20kg of downforce in really high speeds.. So that's a sack of potatoes in the trunk. Except that I don't need that sack now!

David: Intressant detta som vi pratade om, invånarna i detta land eller hur? Ja vi får väl se vad vi kan göra för kopiering!