Proper diffuser option for the ///M

B

Beedub

Lifer
 Sutton Coldfield
functional Diffuser...

Well it seems theirs a functional rear bolt on diffuser option for our cars... Alot of people have that stuck on upside down piece of tat which for me at least is total sacrilege on such a serious sports car ... This one may be abit aggressive for some but extends out and really should smooth out the air from the rear of the car.... and actually provide some function.

NOTE** - Rpi or similar small silencers are required.

Whats peoples opinion?

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john-e89 said:
Complete waste of money on a road car unless you like the look.
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Plenty of track users on here.......

Also as a side note.. most of the performance modifications we do to these cars are pretty pointless on a road car..... id wager only certain people would buy the above diffuser HOWEVER, id much rather have a function piece /or None at all than the recent trend of stick-on upside down vortex generator thing which is again imo of course sacrilege on such a performance orientated model.
 
Beedub said:
john-e89 said:
Complete waste of money on a road car unless you like the look.
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Plenty of track users on here.......
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Indeed, which is why I said road car meaning just road users. You didn't mention track users, but then I didn't take that into consideration either so for a road car a waste of money, for a road and track car who knows without data? Would it really gain anything worth the cost of it for a car used on the roads as well?
 
I like it, though that sticker looks bogus, and again, is easy removable. It does have function over form, and I bet it does as advertised.. Byron, there is another option mate, the Varis rear pieces are quite nice too, but at more than 8 times the price of this.if your looking for something that functions, this is a no brainer.
 
For 90% of the people who brought this it was for cosmetic reasons. For the other 10% it's only a cosmetic thing 90% of the time!! Then it might actually work and do something at high high speed on an aurobahn or track.

Saying that I like it have been looking st them. I think I may well make something like it one day. But it dose look like lots of easy to make anodised aluminium bolted together.
 
Beedub said:
thanks for the discussion on this one peeps, always good to hear what the masses think!
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Seriously I'm not trying to be controversial but my thoughts are that a Z4M used for road and track wouldn't generate enough cornering speed to make this of any use, as for straight line stability Is there a problem with that in the first place with the said car? Surely you need front aero and under car panels to channel and control air to make it of any use out the back which again you couldn't generate on a fairly stock car.
 
Beedub said:
functional Diffuser...
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I just can't see the point really in our country on our roads. I do track my car quite a lot but it is not a dedicated car that get' trailered to the track, if I were to have such a thing I very much doubt I would start with one of these cars. I like the fact I can drive there and back and do other stuff with it. Coupled with the reality that I don't live next door to Spa or some extremely high speed track where that kind of aero grip might be useful, plus the need to balance it with a bloody great splitter on the front if you're going to do it properly, means it's a no for me. Agree those stuck on faux 'diffusers' are absolute cack though, belong on seat leon etc, or most modern turbo hatch stuff it seems, bizarre.
 
john-e89 said:
Beedub said:
thanks for the discussion on this one peeps, always good to hear what the masses think!
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Seriously I'm not trying to be controversial but my thoughts are that a Z4M used for road and track wouldn't generate enough cornering speed to make this of any use, as for straight line stability Is there a problem with that in the first place with the said car? Surely you need front aero and under car panels to channel and control air to make it of any use out the back which again you couldn't generate on a fairly stock car.
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nah didn't think that at all... just enjoying everyones opinions :) :)

id hazard guess in a straight line this would probably be very functional, but again , you'd probably have to be going 80mph plus for it to start cleaning the turbulent air ??? i have no idea... In the world of trying to make our z4s the best their it can be.... and seeing many similar type setups for elises Exgie, Vx, .... plus ontop of all that, it looks very cool.....
 
They only work when they're fed smooth air but the underbody is not blanked off.

Their job is not to tidy up turbulence but to create a larger exit than the opening. This creates a pressure difference which creates the downforce.

This is a Cayman to show what I mean:

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I reckon over the top stuff like that diffuser looks stupid on anything but a dedicated track car. I also question how functional it would be without a lot of other aerodynamic improvements.
 
I like it but it would be a pain 90% of the time and (as said) would function only with other aero mods. I've not considered fitting a splitter or diffuser largerly because they would ground all the time.
 
You'd be better off paneling the rest of floor and doing something down the sides I imagine. That would be my stealth route and then if you need more, splitter and diffuser?

One thing to be careful of is keeping the diff cool if you decide to panel...
 
Steve84N said:
They only work when they're fed smooth air but the underbody is not blanked off.

Their job is not to tidy up turbulence but to create a larger exit than the opening. This creates a pressure difference which creates the downforce.
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Totally true. A diffuser must be fed undisturbed/unturbulent air, and only then the lamellae can create an underpressure as the size of the cavety grows.

With the e85/86 z4, it has a huge windtrap on the underside in the shape of the gearbox area which is not covered up which'll create a lot of turbulence.
On the e46 and e89 bmw did cover up this area with a plastic undertray. But even with these cars the exhaust isnt covered up, so its not 100% flat.
The only thing a diffuser can do for the z4 (like the aero kit diffuser) is filling up the holes between bumper and chassis, reducing another stock windtrap
 
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