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Old 05-13-2019, 11:57 PM
  #31  
FourT6and2
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Originally Posted by krell View Post
I'll see the underside of my GT3 in a few days but I don't believe a side delete is going to have much if any impact on the rear aero. The OEM mufflers are mounted high up in the rear bumper so only the piping may be in the air stream, not unlike the side deletes.
There is no wheel liner in the rear. So removing the side mufflers creates an opening from the rear wheel all the way to rear bumper and underneath the car. I have no idea if it affects aero or not. But I don't think anybody has stopped to ask if it does. My first thought is that it must. Doesn't mean it's a huge impact, but I'm willing to bet it affects aero to some degree, even small. I'm just curious to know what the actual effect is. Too bad wind-tunnel testing isn't as popular as dyno testing lol...

If louvres in the front fender help increase downforce by venting high-pressure air, I'm sure creating a huge gaping hole behind each rear wheel inside the body panels does something as well, either good or bad.

I think we can all agree if the diffusor on that GT3 prototype makes it to production it will be bad @ss.
Yeah, if that diffusor makes it to production I bet all the .2 GT3/RS owners will want one for sure.
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Old 05-14-2019, 12:14 AM
  #32  
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Originally Posted by FourT6and2 View Post
There is no wheel liner in the rear. So removing the side mufflers creates an opening from the rear wheel all the way to rear bumper and underneath the car. I have no idea if it affects aero or not. But I don't think anybody has stopped to ask if it does. My first thought is that it must. Doesn't mean it's a huge impact, but I'm willing to bet it affects aero to some degree, even small. I'm just curious to know what the actual effect is. Too bad wind-tunnel testing isn't as popular as dyno testing lol...

If louvres in the front fender help increase downforce by venting high-pressure air, I'm sure creating a huge gaping hole behind each rear wheel inside the body panels does something as well, either good or bad.
We don't need a wind tunnel, just a CFD program and a well versed person to model both setups for us.
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Old 05-14-2019, 12:15 AM
  #33  
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Originally Posted by krell View Post
I think we can all agree if the diffusor on that GT3 prototype makes it to production it will be bad @ss.
Looks? Yes!

Function? Maybe?

I have this absurd diffusor on the *** end of one of my cars and yet it makes substantially less down force overall than the current RS.

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Old 05-14-2019, 01:50 AM
  #34  
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downforce for front and rear of 991.1 GT3 RS

I cannot remember the source...came from some post on Rennlist if I remember right.
991 RS makes a surprising amount of downforce even at legal speeds...but really noticeable at higher speed corners and braking...even by an amateur like me...
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Old 05-14-2019, 12:28 PM
  #35  
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Almost no road cars make usable aero grip at all. Most people even on track will not require downforce as the fastest parts of track are straight...

That being said:

Ride height greatly affects downforce as the less air getting under the front bumper creates a suction (low pressure area) under the car and forces more air over and around the car. Diffusers are for efficiency- for arguments sake if they make same aero downforce as a wing, they actually make it with less drag.

Big wings are draggy. Viper ACRX for example. It has massive drag, more brute force aero than any road car ever released at the time. At high speed tracks like Fontana, it was almost impossible to get over 150 mph because of drag.

Cars which rely on lower body sculpting to make Downforce aka 'tunnel cars' like the old GTP cars- they stick and can still hit high velocity everywhere. Of course, if you hit a bump you lose all your aero...so they have to balance the safety of that out (or let people backflip at 160mph) with a little ride height and some top body winging.

At 80mph you can feel noticeable downforce from the front end in a car like the senna, P1, acr-x etc. there is a distinct lack of 'hunting' from the steering wheel, steering speed slows down a bit etc.

Ride height and suspension grip are much more noticeable in porsches vs aero and it will always be that way until you drive a GT4 clubsport or GT3 cup. Then, you really get some wild aero sensation and the dreaded 'aero push' aka too much rear wing that the front is not gripping. You get a big understeer with too much rear DF and poor compensation measures from front.

Active aero is a different subject altogether but lets just say it works really well.


This new diffuser wont make 1000 lbs of donwforce but it will make 50-100 in a very efficient way. The rear wing will make 1-2x that and the front chin spoiler and vents will make another 70-150lbs at high speeds. So maybe, they make 300-400lbs of downforce at 150mph. Not really sure that Porsche could do more and keep the ride height passing EPA/DOT/NHTSA /TÜV

If you slammed the nose down (race mode active ride height like Ford GT/ Senna/p1) then you could double all the chin spoiler and diffuser numbers and REALLY feel it. That could be almost 700lbs of DF.

Viper at 150-160 and P1/ Senna at 150-160 are rock solid stable.

CGT at same speeds is not. It feels floaty by comparison. I have not done that speed in a GT2RS yet but likely will be planted but not like viper or senna. Different leagues, like a radical vs a GT3...

Once you get cars making 1000+ it's amazing to experience.

An LMP3 car is really the most incredible thing- 3000lbs of downforce so you are 30-40mph faster through some corners- stuff like T1 at somoma or the esses, Eau Rouge, final corner at road atlanta etc are all easy flat out no lift no hesitation.
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Old 05-14-2019, 12:41 PM
  #36  
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Originally Posted by C.J. Ichiban View Post
Almost no road cars make usable aero grip at all. Most people even on track will not require downforce as the fastest parts of track are straight...

That being said:

Ride height greatly affects downforce as the less air getting under the front bumper creates a suction (low pressure area) under the car and forces more air over and around the car. Diffusers are for efficiency- for arguments sake if they make same aero downforce as a wing, they actually make it with less drag.

Big wings are draggy. Viper ACRX for example. It has massive drag, more brute force aero than any road car ever released at the time. At high speed tracks like Fontana, it was almost impossible to get over 150 mph because of drag.

Cars which rely on lower body sculpting to make Downforce aka 'tunnel cars' like the old GTP cars- they stick and can still hit high velocity everywhere. Of course, if you hit a bump you lose all your aero...so they have to balance the safety of that out (or let people backflip at 160mph) with a little ride height and some top body winging.

At 80mph you can feel noticeable downforce from the front end in a car like the senna, P1, acr-x etc. there is a distinct lack of 'hunting' from the steering wheel, steering speed slows down a bit etc.

Ride height and suspension grip are much more noticeable in porsches vs aero and it will always be that way until you drive a GT4 clubsport or GT3 cup. Then, you really get some wild aero sensation and the dreaded 'aero push' aka too much rear wing that the front is not gripping. You get a big understeer with too much rear DF and poor compensation measures from front.

Active aero is a different subject altogether but lets just say it works really well.


This new diffuser wont make 1000 lbs of donwforce but it will make 50-100 in a very efficient way. The rear wing will make 1-2x that and the front chin spoiler and vents will make another 70-150lbs at high speeds. So maybe, they make 300-400lbs of downforce at 150mph. Not really sure that Porsche could do more and keep the ride height passing EPA/DOT/NHTSA /TÜV

If you slammed the nose down (race mode active ride height like Ford GT/ Senna/p1) then you could double all the chin spoiler and diffuser numbers and REALLY feel it. That could be almost 700lbs of DF.

Viper at 150-160 and P1/ Senna at 150-160 are rock solid stable.

CGT at same speeds is not. It feels floaty by comparison. I have not done that speed in a GT2RS yet but likely will be planted but not like viper or senna. Different leagues, like a radical vs a GT3...

Once you get cars making 1000+ it's amazing to experience.

An LMP3 car is really the most incredible thing- 3000lbs of downforce so you are 30-40mph faster through some corners- stuff like T1 at somoma or the esses, Eau Rouge, final corner at road atlanta etc are all easy flat out no lift no hesitation.
Any theories on the effect of removing side mufflers and center muffler, regarding aero? I'm sure it's small, but when people obsess over the details but ignore three large, gaping holes they've just created, it makes me chuckle.
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Old 05-14-2019, 01:56 PM
  #37  
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Originally Posted by ILLCOMM View Post
Looks? Yes!

Function? Maybe?

I have this absurd diffusor on the *** end of one of my cars and yet it makes substantially less down force overall than the current RS.

That's not a proper diffusor anyway. It needs to start well underneath the car as opposed to just hanging off the bumper.
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Old 05-14-2019, 02:03 PM
  #38  
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Originally Posted by Quikag View Post
I think half the people here would have more fun bit*h slapping a Miata around the track sideways than taking their GT3 to 60% of its capabilities, but their ego won’t permit them to drive a lesser car.
I just put together a full race spec'd Miata and am piloting it for 9 races this season. The Miata is a blast - and while my other track car is a fully outfitted Audi TT Quattro, I was 2nd place first time out driving it this season with the Miata.
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Old 05-14-2019, 03:27 PM
  #39  
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When I'm on the freeway and the wing pops up on my Touring I feel the car just grip the pavement. Incredible really.... If I'm going fast enough I can almost catch a wheelie with the amount of downforce on the rear end. Gives me wood.
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Old 05-14-2019, 03:39 PM
  #40  
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Originally Posted by TexasPorschelover View Post
When I'm on the freeway and the wing pops up on my Touring I feel the car just grip the pavement. Incredible really.... If I'm going fast enough I can almost catch a wheelie with the amount of downforce on the rear end. Gives me wood.
Post of the day!
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Old 05-14-2019, 04:26 PM
  #41  
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Originally Posted by FourT6and2 View Post
There is no wheel liner in the rear. So removing the side mufflers creates an opening from the rear wheel all the way to rear bumper and underneath the car. I have no idea if it affects aero or not. But I don't think anybody has stopped to ask if it does. My first thought is that it must. Doesn't mean it's a huge impact, but I'm willing to bet it affects aero to some degree, even small. I'm just curious to know what the actual effect is. Too bad wind-tunnel testing isn't as popular as dyno testing lol...

If louvres in the front fender help increase downforce by venting high-pressure air, I'm sure creating a huge gaping hole behind each rear wheel inside the body panels does something as well, either good or bad.
I can't tell you how much downforce is lost by removing the side mufflers but I bet its a lot less than removing the center muffler. I think it's probably just a drag penalty that's offset with the weight reduction.

The Cup cars don't run the side mufflers and don't have a filler panel. It's a spec series but that'd be an easy fix if it were a problem. The GT3R has a closeout panel/eliminates the bumper cover in the area behind the tires. Some with the RSR.

To me, it would seem the effect of removing the side mufflers would be similar to having your windows down vs. not. While the window opening is larger and has more air moving past, I'd think the drag penalty is much higher than removing the side mufflers. The air flow isn't super clean with the mufflers in place anyways and there is a tire right upstream causing that area to be a low pressure zone. So, the penalty may be minimal but every little bit of efficiency counts in a non-spec racing class.

Removing the rear muffler will probably reduce the effectiveness of the diffuser considerably but as CJ and others have mentioned, the ride height of the car and the stock diffuser itself isn't designed to really make a ton of downforce. But it does make some.

The best option would be to cover up all the "holes" with a wider and longer diffuser with taller fences (at least on the outermost fence) to help reduce the tire wash into the diffuser. Isolating/blocking of turbulent air from getting under the car and/or disrupting the diffuser is a big win for aero efficiency.

Regarding shops to run CFD, they are out there and some of them are working on these types of things today. To name a couple, there is Verus Engineering and Next Rev Motorsports with the later testing a solution for the 2RS with 311RS. 311RS is also a importing Manthey Racing parts for the 2RS.... So, it'll be interesting what comes out in the next year or so. I'm definitely interested in seeing well engineered aero parts for the 3RS platform coming to market.
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Old 05-14-2019, 04:55 PM
  #42  
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Originally Posted by mdrums View Post
I cant tell any difference in my GT3 vs my 2017 GTS on the street as far as downforce. I can defiantly tell at Sebring, especially in Bishops bend at 110-120mph.
+1
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Old 05-14-2019, 05:08 PM
  #43  
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Originally Posted by TexasPorschelover View Post
When I'm on the freeway and the wing pops up on my Touring I feel the car just grip the pavement. Incredible really.... If I'm going fast enough I can almost catch a wheelie with the amount of downforce on the rear end. Gives me wood.
the funny thing is.. some people actually believe this of their own cars, and read your post and go "a-ah!.. so it's not just me.. this must mean that the big spoiler on my RS on which i eat my sandwiches actually does something"... it's a slippery slope of self-convincing placebo effect. To CJ's point, i have driven a Senna for enough time, at road speeds which are probably not ok to mention, to realize that this was the first car i ever drove which had real downforce around 100mph (above or below that a little bit).. it was a truly strange feeling to have that car really dig in hard as you accelerated in turns at speeds which most other cars would have experienced an off. I've never been in anything which gave that sensation.. i wish I could have taken that beast on track, i can't imagine what that would have been like. I just mention this to say that most people feel mechanical grip and wish it were aero.. it ain't, your wings and scoops are about as important as your stickers in a road context.

track, totally different animal.
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Old 05-14-2019, 05:09 PM
  #44  
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Originally Posted by S.White View Post
Regarding shops to run CFD, they are out there and some of them are working on these types of things today.
The trouble is that the areas we're talking about are very complex to model, as you say largely disturbed air flow through the body. If you're going for direction CFD will help, but it won't be good for absolute ie aero balance without a reference tunnel run to verify the model. There are a couple good rolling floor wind tunnels that anyone can book. Usually 1/2 day to 1 day minimum though.

I agree with the idea that the center muffler is worse than the sides.
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Old 05-14-2019, 05:13 PM
  #45  
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For all of us goofballs that have deleted the center muffler, I guess we need a company to design a diffusor extension or something to close up the open area.
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