911R's rear diffuser
10-27-2016, 09:39 PM
#91
Burning Brakes
Join Date: Jul 2016
Location: Northeasterner living in the South
Posts: 1,232
Received 37 Likes
on
25 Posts
Gentlemen.....I won't have this blasphemous talk!!! I just won't have it!!
Porsche is PERFECT....and every feature they put in the GT cars makes them faster and race ready!!! Don't even think about questioning this Fact!!!!!
Porsche is PERFECT....and every feature they put in the GT cars makes them faster and race ready!!! Don't even think about questioning this Fact!!!!!
11-01-2016, 06:52 AM
#92
One things for sure - the diffuser is very low!
I know of many (most?) that have been damaged coming off the transporter. Both mine and other one delivered at same time are waiting for replacements under warranty.
I caught it last night on a relatively small speed bump, so glad it being replaced. (I'm hoping to keep the old one to use and have the new one on standby). I didn't put a front lift on my car, but the rear would be more limiting anyway, IMO. Just needs some care, but obviously worth it, for the ground effects...
I know of many (most?) that have been damaged coming off the transporter. Both mine and other one delivered at same time are waiting for replacements under warranty.
I caught it last night on a relatively small speed bump, so glad it being replaced. (I'm hoping to keep the old one to use and have the new one on standby). I didn't put a front lift on my car, but the rear would be more limiting anyway, IMO. Just needs some care, but obviously worth it, for the ground effects...
11-01-2016, 10:18 PM
#95
Rennlist Member
Join Date: Jan 2013
Location: West Vancouver and San Francisco
Posts: 4,268
Received 1,241 Likes
on
609 Posts
Thanks for posting, but from that list, for performance I'd take the R, because it will be generating a lot less drag. There aren't many 186mph corners in the world, for a road car. (Obviously the d/f will help under braking at the end of the straight)
So, pretty much the 90-100mph that's most relevant for faster corners of a race track I'd say. If RS at 94 mph is 193lb/88kg, then it's not doing much at all
We can assume the R is generating none in terms of feel, GT3 negligible. RS - my guess is it generates massive psychological levels of downforce....
On a non de-restricted road, downforce is not going to be a factor at all. On an autobahn at 180mph plus where it probably helps if there's a bend. Most likely the real reason for a big wing! (+ the racer 'look')
So, pretty much the 90-100mph that's most relevant for faster corners of a race track I'd say. If RS at 94 mph is 193lb/88kg, then it's not doing much at all
We can assume the R is generating none in terms of feel, GT3 negligible. RS - my guess is it generates massive psychological levels of downforce....
On a non de-restricted road, downforce is not going to be a factor at all. On an autobahn at 180mph plus where it probably helps if there's a bend. Most likely the real reason for a big wing! (+ the racer 'look')
First, unless you are driving completely in a straight line, R's aero set up will disadvantage it in terms of performance. Drag has much smaller role than downforce on cars with this low levels of downforce and high-power engines.
Second, 193lbs of downforce at 93MPH is not "not doing much at all". It's a freaking 4-7% more traction in fast corners, which in turn results in 3% higher speed through such corners, but also about 3% higher exit speed from such corners, and thus all the way through the following straight (tapering down on longer straights due to increased drag). It also helps with braking, shortening braking distances from high speeds by up to 6%, and thus enabling going at top speeds longer.
And if those numbers seem like not much, just consider that 3% faster is almost 2 seconds per minute or difference between Cayman GT4 and Corvette Z06 or Lambo Huracan. 2 seconds per minute is enough to thoroughly intimidate someone on track.
And this does not take into account other positive effects of downforce, such as reducing the impact of elevation changes on available traction, which adds confidence.
So if performance is the goal, even seemingly small numbers of downforce matter. It does not have to be something comparable to the weight of the car to matter.
11-02-2016, 04:08 AM
#96
If you want to get really technical, the stripes on the R make it go 7.36% faster everywhere (unless it's dark), so it's quicker anyway. They also add confidence and don't add much to the weight of the car.
Depending on the thickness of the vinyl, they do add drag to be fair, but that's counteracted by the reduction created by the Porsche badge being a sticker rather than metal. (Not a lot of people realise that a metal badge would disrupt the airflow over the car, away from the roof indentations, almost negating the speed gain created by the go-faster stripes). Attention to detail - that's what Porsche is all about.
PS Since my diffuser has a slight dent in it, it's virtually impossible to drive in a straight line, due to the resultant lack of downforce.
Depending on the thickness of the vinyl, they do add drag to be fair, but that's counteracted by the reduction created by the Porsche badge being a sticker rather than metal. (Not a lot of people realise that a metal badge would disrupt the airflow over the car, away from the roof indentations, almost negating the speed gain created by the go-faster stripes). Attention to detail - that's what Porsche is all about.
PS Since my diffuser has a slight dent in it, it's virtually impossible to drive in a straight line, due to the resultant lack of downforce.
11-02-2016, 08:56 AM
#97
Race Director
Originally Posted by Footsoldier
If you want to get really technical, the stripes on the R make it go 7.36% faster everywhere (unless it's dark), so it's quicker anyway. They also add confidence and don't add much to the weight of the car.
Depending on the thickness of the vinyl, they do add drag to be fair, but that's counteracted by the reduction created by the Porsche badge being a sticker rather than metal. (Not a lot of people realise that a metal badge would disrupt the airflow over the car, away from the roof indentations, almost negating the speed gain created by the go-faster stripes). Attention to detail - that's what Porsche is all about.
PS Since my diffuser has a slight dent in it, it's virtually impossible to drive in a straight line, due to the resultant lack of downforce.
Depending on the thickness of the vinyl, they do add drag to be fair, but that's counteracted by the reduction created by the Porsche badge being a sticker rather than metal. (Not a lot of people realise that a metal badge would disrupt the airflow over the car, away from the roof indentations, almost negating the speed gain created by the go-faster stripes). Attention to detail - that's what Porsche is all about.
PS Since my diffuser has a slight dent in it, it's virtually impossible to drive in a straight line, due to the resultant lack of downforce.
11-02-2016, 12:55 PM
#98
Nordschleife Master
If you want to get really technical, the stripes on the R make it go 7.36% faster everywhere (unless it's dark), so it's quicker anyway. They also add confidence and don't add much to the weight of the car.
Depending on the thickness of the vinyl, they do add drag to be fair, but that's counteracted by the reduction created by the Porsche badge being a sticker rather than metal. (Not a lot of people realise that a metal badge would disrupt the airflow over the car, away from the roof indentations, almost negating the speed gain created by the go-faster stripes). Attention to detail - that's what Porsche is all about.
PS Since my diffuser has a slight dent in it, it's virtually impossible to drive in a straight line, due to the resultant lack of downforce.
Depending on the thickness of the vinyl, they do add drag to be fair, but that's counteracted by the reduction created by the Porsche badge being a sticker rather than metal. (Not a lot of people realise that a metal badge would disrupt the airflow over the car, away from the roof indentations, almost negating the speed gain created by the go-faster stripes). Attention to detail - that's what Porsche is all about.
PS Since my diffuser has a slight dent in it, it's virtually impossible to drive in a straight line, due to the resultant lack of downforce.
12-27-2016, 02:40 PM
#99
And the undertray would be carbon too? Again, unless I'm badly mistaken, the undertray's purposes include protecting the engine (in addition to smoothing the airflow under the car), and from time to time can itself take a hit from speedbumps, etc. Probably carbon fiber is more suited to this use than to being used for the fins, but is it really the best choice? I'd prefer metal.
So while it's great that you are making an aftermarket version, seems to me it would be even greater if you considered some other materials. And if you make something like this for 996s and 997s, please let me know!
12-27-2016, 03:18 PM
#100
Technical Guru
Rennlist Member
Rennlist Member
Carbon fiber, unless I'm badly mistaken, is not. Indeed, while I know there are different kinds of carbon fiber, did anyone every come up with a carbon fiber that could work as well as a bumper as the regular mumper material? For these fins, I think you'd want something at least as flexible and impact resistant.
12-28-2016, 01:42 PM
#101
The fiber selection is not so much the problem as is the choice of compatible resin. For a rear diffuser that would need to withstand debris impact (but does it really?), something like Bayer Bayflex works really well (used on snowplow blades) and you could probably spec a cheap milled fiber. However the weight benefits would probably be lost.
Slightly less off topic, am I correct that it makes no sense to think one can reduce weight with carbon fiber bumpers (unless one doesn't mind regularly replacing them when they get damaged)?
Thanks!
12-28-2016, 07:40 PM
#102
Technical Guru
Rennlist Member
Rennlist Member
The bottom (wear) section of the blades on commercial snow plows are a glass filled elastomer. Bayflex was used for this the last time I was involved with any type of casting. In that application there is no benefit to using carbon fiber. In a passenger car you might want the diffuser to be the sacrificial object instead of the floor pan? I would trust the automotive, mechanical and material science engineers that Robert Linton (unlike 99.95% of the automotive aftermarket) employs to have worked out the details. If you are balancing longevity with cost than metal might be the more appropriate material (aka Porsche knows best?)
12-29-2016, 06:43 PM
#103
In reality, the tray might be made from a high temperature composite (BMI), the fins might be made of a less stiff carbon fiber, might have a bit of kevlar mixed in for tear resistance and/or even might have a bit of glass fiber incorporated to deal with some of the problems noted above. In any case, please forgive my shorthand for saying carbon fiber as a generic.
Last edited by Robert Linton; 12-29-2016 at 07:26 PM.
12-29-2016, 09:39 PM
#105
Though based on some other posts above, it sounds like it might make sense to consider the fins a disposable item, as front lip spoilers sometimes are. In that case, a more disposable material might be the best choice. I don't know what Porsche used for their cup spoilers, but as they apparently sold for as little as $100, it was probably a good choice.