A few modifications...

Gustavo7 said:
I think you missed the point on my Cd vs downforce features of the z4m but that's fine.
Click to expand...
Yes I know you said that but I dont see how 2 small ridges in the bonnet will create significant downforce.
As for the diffuser I think its very debatable if that acts as a diffuser. The ducts originate at the rear of the diff (where the diff heatsink obstructs the airflow) and then it vents out at the rear. A diffuser only works if an airflow is created that has a speed significatnly higher than the driving speed of the vehicle. I cant see that happening with the diff heatsink in its path (and the gitter at the end). Thats why I think that that diffuser is more like ducting to guide away the heat from the diff to ensure the diff is cooled enough.
Even the normal z4 diff already has a finned cover with a similar scoop guiding air to it in the bottom tray, and thats an open diff with less power and that already can get pretty hot (too hot to comfortably touch after a spirited drive).
The z4m has a clutch operated lsd that gets much hotter (due to the friction of the clutch, and of course due to more power) so cooling becomes a real issue (therefore it also needs thicker oil). Normally performance cars with a clutch lsd have a seperate diff cooler (so piping and a radiator) but bmw does it this way. But I just cant see air flowing faster through those heat sink fins than the speed of the car, and that is imho a must to let it work as a downforce creating diffuser, because you can only create underpressure/ground effect by higher air speed than the vehicle speed.
Besides that there are no differences imho.

as for diffusers, this is imho a 'real diffuser':
diffuser_enzo.gif
Where there are long unobstructed ducts underneath a car with a flat underside. Thats where a real underpressure can be created by accelerating the air

And 99% of diffusers you see on current cars are more of a fasion fob not actually contributing on downforce.
you know, like this
kuga_rear_silver.jpg
or this
S3_Rear_Bumper.jpg
 
The ducts above the fangs in the Z4M front bumper are placed in a zone of high pressure when the car is moving forwards. The ducts have an opening aperture which is around 8x times larger than the small aperture at the rear of the duct, which is mostly blocked off. This must surely increase air pressure within the duct itself as the car travels. I would therefore suggest that this effectively increases the effectiveness of the fangs to act as front spoilers rather than for cooling the brakes. You can do the maths... :P
 
it can only act as a spoiler if the air can move freely away and a zone of underpressure is created. That is not the case.
There is no 'underside of the aircraft wing' so to speak. It its current form its a funnel concentrating air against the tyre (maybe against the disc if the wheels turn in). I dont see a great aerodynamic advantage in that, only a possible cooling advantage, but not nearly as effective as the ducting Vanne has made, but that wouldnt be suitabe for a daily driver in cold/wet western europe where lots of moisture and debris would be guided toward the disc and wheel bearing, thats why thats mostly a race/trackcar mod.
So I see those ducts as what a car maker can ultimately do to create some cooling to the discs/wheelwell without directly guiding in all kinds of grime debris and whatnot to the disc/bearing in regards to what an everyday daily car in cold wet western europe or US eastcoast has to cope with on the road like race cooling ducting would do.
 
If the blanking plate was not situated at the rear of the duct there would be less pressure in the ducts at any given speed (I've tested this with my Z3MC and a Magnehelic pressure gauge). The increase in pressure in the Z4M's ducts will cause air to "spill" under the fang creating the under pressure required.
 
if air spills under the fangs, how does that create underpressure? More air means more pressure.
And how exactly have you measured the air pressure in the ducts? do you have any photo/video archive?
a wing/spoiler can only create downforce if the pressure under the car is lower than above the car.
 
Did this years ago with this kit:

48Magnehelic_and_dashdyno.jpg


And produced the recordings and graphed them as the pink trace which compare to the theoretical pressure increase:

Frontalpressureincrease.jpg
 
So the pressure in the fangs increases with speed. That is logical as its an obstruction in air flow.
How does this differ to for example a fixed point on the bumper. That would also recieve a similar curve and increase in pressure (force of drag) I think?
And between where and where is the pressure differential? where and how where the hoses/hose ends situated? (place, direction, you have a photo of that?)

But I dont really see a point where you create underpressure related to this as that is needed to create downforce.
Obviously any increase in downforce results from an increase in drag (resulting from pressure above ambient) but that doesnt mean that any increase in drag automatically results in an increase in downforce.


Anyhow this turns into an interesting discussion (a bit sidetracked from vanne's mods, but still regarding features of his mod) because the aerodynamical properties you speculate/contribute to the fangs are somewhat the opposite of the aerodynamical properties gustavo7 speculated the fangs contribute to, and again opposite to what I think the fangducts are for (I think they just offer up some drag to get some cooling :lol:)
 
The Magnehelic Pressure Gauge has 2 tubes, one is placed in the location under test (front duct, airbox etc.) and the other is kept inside the car.

See: https://www.youtube.com/watch?v=-ZaDO7NbN_Y In this video, one end was placed inside the air intake. When I lift off, you can see the measurement of ram pressure inside the intake. If I'd set the Dashdyno to record speed, it's simple to plot the dynamic pressure at any speed by watching the video replay.
 
Ok, interesting, but then where is your data that shows that the ducts actually create an underpressure under the fangs compared to having no ducts?
Also I recon that the position in how the tubes are placed is pretty difficult/critical because of the venturi effect.

I understand/think its logical that pressure rises in the ducts if blanking plates at the rear are placed because it will act more like an air sack, but that still doesnt show that that actually creates more downforce. It just shows that the blanking plates create more drag.
I think those plates are maybe there so that the air is more funneled (more pressure differential between location in front of the plates compared to behind), so the air through that hole moves more quickly and is maybe targeted more/has more reach towards the brakes if the wheels are in a turning position. I dont know if the tyre can clear that duct if you steer.

Also those blanking plates look a bit like an afterthought. the prefacelift inner fender liners already have the cutouts for the fangducts (which serve no other purpose imho) so they already developed/designed the shape of the z4m with its fang ducts when they developed the initial prefacelift z4, but when actually making/testing the z4m they decided that the outlet side of the fang ducts should have been smaller and created a (very unaerodynamical) blanking plate with a small hole. So imho they were for some reason more interested in getting that small hole to concentrate that air going into the wheelwell than the drag it would create.
 
The blanking plates are there for economical reasons I think, and contamination - they stop a lot of dirt.
Mine's completely blanked right now with custom removable plates.
The more blanked off intake holes in the front, the lower the drag.
See BMW's Efficient Dynamic model's, the have closing flaps inside the grilles, for when cooling is actually needed.
The more air that goes thru the engine bay, the worse the drag basically.
The only channelling of air to the wheel arches taht would LOWER the drag is the more recent air curtains past the front wheels everybody use nowadays, at the rear edges of the bumper:
http://s1.cdn.autoevolution.com/images/news/an-in-depth-look-at-how-bmw-s-efficientdynamics-works-70177_1.jpg

My blanking plates on/off for trackdays:
http://rejsa.nu/im/user/2730/2016-07-04-15-00-58_image.jpeg
http://rejsa.nu/im/user/2730/2016-07-04-15-06-02_image.jpeg
 
Yup, thanks, my mates think it looks oem, extremely hard to pick unless you get up really close.. dropped my oil temps between 7 and 10 degrees. Not sure if it's had an effect on brake cooling.. the cams and vanos refresh (seals, pump disc and chain guide) install was 1500 pommy pounds. But that also included the Labour to fit and modify the oil cooler duct, chain guides, shims and water temp sender and paint and fit the new GC front sway Bar. Also included New oil and new coolant.. and a few seals here and there..
 
ah this car, I like it alot!! :D looking awesum there Vanne... I'm liking the upgrades... let us know how it goes next time you out at the track. :driving:
 
Vanne said:
I do mate, but unless you have an s54 tucked into that si, id say you might be outa luck. What parts are you looking for? I have most of my stock stuff in the garage..at any rate, when your in town, don't forget to call in for a scooner or ten. Always nice to talk cars. ;)
Click to expand...

Hey Chap, unfortunately not, Im running the standard 3.0 si. not after anything specific really, just any toys which you might not have use for!

I got in a couple of days ago and currently staying at the W in Habtoor City. Flying back out again on thursday night to Riyadh (joy!) but back next month again for three days also. If you are around during the next couple of days drop me a PM! :)

Faz
 
That really is a very tidy install well done.

I maybe over in Dubai next year we try and visit once a year. My best friend lives out there. Unfortunately for us he left his apartment opposite the palm and now lives JVT!! And no taxi drivers seem to know there way around. Every time we get a taxi we have to direct them. And sometimes that can be difficult because it dose all look the same. Any way if i pop over i will PM you would be nice to see this in the flesh.
 
Thursday night to Rhiyad?... Lol you might be in luck if your going with EK,I might be driving you there.. pm me your flight number. Sadly before than a bit flat out untill the 27th, after that, let me know for beers..

Monkey, anytime mate, anytime at all. ;)
 
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