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      12-30-2016, 01:34 PM   #1
zachbooze
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Thinking about aero...

Hey guys, I am planning on picking up the APR Wing/Splitter later on in the coming season and I stumbled upon this diffuser too. Is a rear diffuser significantly functional on these cars?
http://fancywide.ru/product/bmw-z4m-...mper-diffuser/
I know some of you have a lot of technical knowledge, so I figured I'd ask you guys
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      01-03-2017, 11:12 AM   #2
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That's a pretty good find. how did you find it? I've searched online a fair bit and that one never popped up.

Would be better if it fully covered over the mufflers but it looks pretty good. Price isn't too bad.

Have you reached out to those guys?
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      01-03-2017, 02:07 PM   #3
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Quote:
Originally Posted by zachbooze View Post
Hey guys, I am planning on picking up the APR Wing/Splitter later on in the coming season and I stumbled upon this diffuser too. Is a rear diffuser significantly functional on these cars?
http://fancywide.ru/product/bmw-z4m-...mper-diffuser/
I know some of you have a lot of technical knowledge, so I figured I'd ask you guys
I have done some research, and asked a shop called trackspec who are making functional vents for z4m and he said that just by the hardware they have used, it has 400x more drag than appropriate hardware. And if they didnt consider that in design, makes him question how much design did they put into the diffuser itself.
So he is considering doing diffuser as well for z4m that is functional.
btw he tests his products at the track with a bunch of lines and some computer data....hes well known in california.
If people get more interested in functional diffuser, I could have him take it more seriously and start asap.
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      01-03-2017, 02:09 PM   #4
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Quote:
Originally Posted by Mirko View Post
That's a pretty good find. how did you find it? I've searched online a fair bit and that one never popped up.

Would be better if it fully covered over the mufflers but it looks pretty good. Price isn't too bad.

Have you reached out to those guys?
I have reached out to them...shipping is 98 worldwide. but like i said in my comments above, I can have trackspec to make a diffuser that will cover mufflers like the varis and that will be 100% for functionality if we can get enough people to buy it.
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      01-03-2017, 03:24 PM   #5
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Quote:
Originally Posted by AriuSen View Post
I have reached out to them...shipping is 98 worldwide. but like i said in my comments above, I can have trackspec to make a diffuser that will cover mufflers like the varis and that will be 100% for functionality if we can get enough people to buy it.
would be interested to see what he would come up with.
That diffuser that I made b4 was mainly cosmetic I'm sure.
I'd be interested in something more functional.

From some of my research one of the most important areas is to restrict the wash of air that comes off the inside of the rear tires.
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      01-03-2017, 03:41 PM   #6
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Quote:
Originally Posted by inTgr8r View Post
would be interested to see what he would come up with.
That diffuser that I made b4 was mainly cosmetic I'm sure.
I'd be interested in something more functional.

From some of my research one of the most important areas is to restrict the wash of air that comes off the inside of the rear tires.
Interested.....explain?
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      01-03-2017, 03:51 PM   #7
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Quote:
Originally Posted by 3GFX View Post
Interested.....explain?
basically the air at the rear tire gets squished & forced out to the sides.
On the outside its not a problem, but on the inside it washes sideways under the car.
If you can catch the air off the tire and force it straight back, air is much more linear under the center & out the back.
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      01-03-2017, 03:56 PM   #8
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So ideally a diffuser should be wide enough to cover the sides of the well? Ideally pushing air backward?
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      01-03-2017, 04:04 PM   #9
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Quote:
Originally Posted by inTgr8r View Post
would be interested to see what he would come up with.
That diffuser that I made b4 was mainly cosmetic I'm sure.
I'd be interested in something more functional.

From some of my research one of the most important areas is to restrict the wash of air that comes off the inside of the rear tires.
Cool!. ill let him know and try to push him to start developing one! ill let him know about your tip!
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      01-03-2017, 04:04 PM   #10
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Quote:
Originally Posted by 3GFX View Post
So ideally a diffuser should be wide enough to cover the sides of the well? Ideally pushing air backward?
Yes.
This one from FancyWide (weird name) does it pretty well.
& AriuSen ... fasteners dont look bad to me.

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      01-03-2017, 04:07 PM   #11
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Quote:
Originally Posted by inTgr8r View Post
Yes.
This one from FancyWide (weird name) does it pretty well.
& AriuSen ... fasteners dont look bad to me.

you have to look at the inner part.
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      01-03-2017, 04:10 PM   #12
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yea but anyway.....im not a aerodynamic expert, but seems like is a good diffuser. is just that the the owner of trackspec is very detailed to minimum stuff.
i am actually tempted to get one, but since trackspec said he would be interested in making one, i opted to wait and see what he comes with.
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      01-03-2017, 04:30 PM   #13
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Quote:
Originally Posted by AriuSen View Post
yea but anyway.....im not a aerodynamic expert, but seems like is a good diffuser. is just that the the owner of trackspec is very detailed to minimum stuff.
i am actually tempted to get one, but since trackspec said he would be interested in making one, i opted to wait and see what he comes with.
Yeah, noticed the inner part after I posted... I agree.
Also, if you look closely the edges are done poorly, ....rough cut with some sort of plasma cutter

I'd also MUCH rather deal with someone in N.Amer.

I wonder what the weight would be?

The other important part is to maintain air getting to the rear diff!!!!!
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      01-03-2017, 05:15 PM   #14
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Quote:
Originally Posted by AriuSen View Post
I have reached out to them...shipping is 98 worldwide. but like i said in my comments above, I can have trackspec to make a diffuser that will cover mufflers like the varis and that will be 100% for functionality if we can get enough people to buy it.
I am interested in a functional one and would prefer someone in North America like Ian.

What sort of timeline? Track season starts in 4 months up here in the frigid north!!
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      01-04-2017, 07:33 AM   #15
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Quote:
Originally Posted by inTgr8r View Post
basically the air at the rear tire gets squished & forced out to the sides.
On the outside its not a problem, but on the inside it washes sideways under the car.
If you can catch the air off the tire and force it straight back, air is much more linear under the center & out the back.
This is apparently correct. Google exhaust blown diffuser. Some F1 teams route the exhaust to push the air past the inside of the rear tire, creating a boundary layer and preventing the air washed off the tire from getting pushed into the diffuser.

https://www.google.com/search?q=exha...lpXBSEGJsJM%3A

Anyway, I would also be interested in a functional diffuser if the Trackspec guy moves forward. Although with a small bench brake, fabricating one doesn't look that difficult.
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      01-04-2017, 10:46 AM   #16
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Quote:
Originally Posted by Mirko View Post
I am interested in a functional one and would prefer someone in North America like Ian.

What sort of timeline? Track season starts in 4 months up here in the frigid north!!
I think 4 months is plenty of time lol. let me get details from him.
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      01-04-2017, 12:45 PM   #17
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Aero is a slippery slope. Far more slippery than suspensions, IMO. And it is FAR more dependent on your skills as a driver, since with added grip quickly disappears when you are SIDEWAYS. It's like the transition from driving on street tires to R-Comps.

That increase in grip level also comes at the cost of terminal speed too. I think aero is more beneficial on cars that have added "lightness". At 3,xxx lbs with driver the lift eliminated, or downforce created at speed isn't significant enough, but at 2,7xx? That same force is far more effective.

The other thing to think about, is how aero affect classing if you're competing. Take BMW CCA CR for example, I believe STOCK classes no aero is allowed. You add a splitter and a diffuser and all of a sudden you're in MOD class, where composite panels, stroker engines with stand alone ECUs, slicks rather than r-comps, and all sorts of exotic setups are common in the name of "competition."

If you're not adding aero for competition purposes, then it does go a long way to improve lap time. As my club racing buddy once commented to me. "[Hack], aero is like crack for racers. Once you go aero you will NEVER want to go back." Or as another CR buddy, after driving my MZ4 Coupe at Buttonwillow, commented: "[Hack], you need aero."

So yeah. If you guys end up making a functional aero diffuser here in the states, loop me in. I'm definitely interested.
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      01-04-2017, 01:07 PM   #18
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Wow, whether it works or not that diffuser looks great! (perfect for a poser like me lol).

What a price too, I expected to see $1350, not $350. That's about the first time I've ever seen a custom part for our cars and thought the price was right!

I'd love to see more pictures, but you need a pretty wild car to pull it off right (lowered, wheels, BBK, other mods etc.). I think I could manage it with my car, but it might be *too* much. Overall stock cars would look like crap with this I think.
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      01-04-2017, 01:20 PM   #19
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I'd definitely be interested in a functional diffuser from trackspec. There is a trackspec autosports (NorCal Bay Area) and a track spec motorsports in (SoCal). Im guessing you are referring to the SoCal one?

Last edited by zachbooze; 01-04-2017 at 01:28 PM..
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      01-04-2017, 01:21 PM   #20
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The inherent problem with any diffuser that will bolt up to the unmodified rear bumper is that it doesn't provide enough of an angle to maximize the venturi effect. From what I've read (on the internet, of course), the more it angles up, the more it expands the air, increasing the draw, or suction from the feeding air. Up to an angle of 10%. Beyond that and apparently the air seperates from the difusser, and much like an airfoil when it stalls, it loses benefit.
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      01-04-2017, 02:03 PM   #21
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Quote:
Originally Posted by Michael9218 View Post
The inherent problem with any diffuser that will bolt up to the unmodified rear bumper is that it doesn't provide enough of an angle to maximize the venturi effect. From what I've read (on the internet, of course), the more it angles up, the more it expands the air, increasing the draw, or suction from the feeding air. Up to an angle of 10%. Beyond that and apparently the air seperates from the difusser, and much like an airfoil when it stalls, it loses benefit.
It's surprising, but there is more angle than initially evident.
From when I did my 1st diffuser fins added to the OE under tray, I would say that there is close to 10% already with a Venturi like curve.
In the pic the bottom of fins are not fully at zero deg.

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Last edited by inTgr8r; 01-04-2017 at 02:23 PM..
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      01-04-2017, 03:24 PM   #22
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I'd be interested in a group by as well.
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