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What a great clear comment!
Thanks.

2 additional questions

1. If the underbelly is well fixed to the chassis the only "deformed "area could be the lip right?
2. In one of the Kylee engineer video (the guy is former AJ HARTMAN consultant and now F1 engineer) he said
(
around 8:50 and up)
" if we lift the front of the splitter up we allow more airnto get under the car resulting in even more increasing of air speed resulting in more downforce.

So all the theory of giving a negative AoA of the splitter is not true?4c09d7435858ef96f56d0f586bcab5f0.jpg

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What a great clear comment!
Thanks.

2 additional questions

1. If the underbelly is well fixed to the chassis the only "deformed "area could be the lip right?

You would think so, but it’s not always the case. Most of this is alleviated due to the adjuster rods being positioned towards the leading edge of the splitter, and the real pressures didn't build up until they reached the middle of the surface area. The leading edge is cutting into the air, not giving it a surface to generate pressures on to. That happens farther back on the splitter and belly pan.

At one point in the video, he speaks about the downward pressure on the top of the splitter. Well... in my experience, it’s more the negative of pressure underneath the splitter that generates the downforce, with most of the drag coming from the top side, so... yeah. Not to say he’s wrong or anything; it’s likely just the difference in automobiles. Stock Cars are a far cry from F1, so it’s likely they are trying for gains using different approaches than we would.

We would run “soft” springs to get the front of the nose down on our cars for a couple of reasons. One, it worked better for us to have a lot of rake in the car at speed. This way, the most amount of downforce was generated from the body surface of the car, and the less air the better underneath. Since we couldn’t run full belly pans, we wanted the smallest amount of air possible under the car, and what air did get under there, we wanted it to move out as fast as possible. Two, our wind tunnel time showed us the best results when the splitter was perfectly parallel to the racing surface, with the undertray kicked up about 7°. This gave the impression that we had the front of the splitter “kicked up”, and in reality, at race attitude (the rake the car has at speed) it was perfectly level with the earth.


2. In one of the Kylee engineer video (the guy is former AJ HARTMAN consultant and now F1 engineer) he said
(
around 8:50 and up)
" if we lift the front of the splitter up we allow more airnto get under the car resulting in even more increasing of air speed resulting in more downforce.

So all the theory of giving a negative AoA of the splitter is not true?

4c09d7435858ef96f56d0f586bcab5f0.jpg
Sent from my LG-H932 using Tapatalk

I’d say those guys opening up the front end of their cars in WTAC are more trying to manage the air moving over and through the body of the car. Downforce comes with Drag, and trying to reduce Drag while keeping your Downforce numbers on target is what the goal is.
 

Boone

Professional Thread Killer
Downforce is created from a pressure differential. This applies whether we're talking about the front or back of the car. For the splitter, you can look at increasing downforce by further lowering the pressure on the bottom of the splitter or increasing the pressure above the splitter. Either way, it's the difference in pressure that matters, so both sides of the splitter matter.

The amount of area the pressure is acting on gives you a force. This is likely why the testing daegoba observed focused on the bottom side of the splitter. There is more area there, thus more opportunity for gains.
 
I've also spoken to them a bit and can vouch that they are very customer-friendly, though I haven't bought anything from them yet. Will be interested in what you end up with from them Boone.
I couldn’t agree more, their front splitter appears to be a great product as well. They use some type of composite, which is then wrapped in an aluminum (I believe). It felt very strong. Here is the universal center vent on my S197 if anyone is interested in fit etc... I’m going to be adding the silver vents soon as well.
 

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ChrisM

Mostly harmless.
1,180
1,419
Exp. Type
HPDE
Exp. Level
3-5 Years
South Carolina
The underside of the newest Mustangs is pure OEM aero porn. Even my wife commented on how dramatic the difference is just looking at it.
 
Great conversation.
So the reason why I'm asking is because I don't think the underbelly could be much more different than this OEM PP1.
Yes maybe adding 1 extra tunnel front diffuser.
Underpanel is block with 12 bolts and screws.
Surface is pretty flat.

So does it make sense to buy or fabricate a brand new one splitter?

However the add front Lip started to generated some downforce.
In the second picture you can see that the entire front end is loosing. All the plastic clips are completely disangage.
In wsir where the average speed is 100mph for 2. 5 miles with 140 top speed the stress on front end is bigger i guess.
After i get back the car in 2 weeks I'm hoping to install front rods to the chassis .
3465588cf6087ecad874be44b368ba6a.jpg019abe9910f1c0fc19a4da02256db5d7.jpg

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Grant 302

basic and well known psychic
But currently the car is shaking like crazy with the splitter on.

Can you tell what direction the shaking is? Up/down or do you feel lateral movement in the steering wheel? What speed does it start to show up?

Since your splitter seems like it might be stiffer than your mounting, it seems possible that it is fluttering and the mounting needs to be stiffened to eliminate.
 
218
369
Exp. Type
Time Attack
Exp. Level
5-10 Years
CA
Can you tell what direction the shaking is? Up/down or do you feel lateral movement in the steering wheel? What speed does it start to show up?

Since your splitter seems like it might be stiffer than your mounting, it seems possible that it is fluttering and the mounting needs to be stiffened to eliminate.

The shakes are stronger on throttle than when coasting. You can see the shakes getting less when I am off throttle and turning and trail breaking into t9 and t1.

There are general shakes through the whole car as well as the steering wheel. It basically feels like a badly bent wheel, accept it gets stronger the faster you go.
I tried multiple tires and wheels and kept rotating them. It`s definitely neither tire nor wheels.
We also did a dyno test and there are no shakes coming from the rear.

The splitter is on the heavier side and really stiff. Connected to the bumper cover and with rods to the bumper support beam in the front. There is no support to the chassis under the car yet as the splitter is not long enough.
I also tried decreasing the AOA from 0 to -1 but this rather makes the shakes stronger.

Removing the splitter solves the problem completely and the car runs super smooth without it.

I am running 550/275 springs, MCS Vorshlag coilovers, Boss ABS module, 2011 stock steering rack, stock front bushings, rear bushings are all spherical accept for the Dif.

The camera arm on the rear window exaggerates the motion quite a bit. It`s not as bad but the car still shakes quite bad at 100-140mph:

 
The shakes are stronger on throttle than when coasting. You can see the shakes getting less when I am off throttle and turning and trail breaking into t9 and t1.

There are general shakes through the whole car as well as the steering wheel. It basically feels like a badly bent wheel, accept it gets stronger the faster you go.
I tried multiple tires and wheels and kept rotating them. It`s definitely neither tire nor wheels.
We also did a dyno test and there are no shakes coming from the rear.

The splitter is on the heavier side and really stiff. Connected to the bumper cover and with rods to the bumper support beam in the front. There is no support to the chassis under the car yet as the splitter is not long enough.
I also tried decreasing the AOA from 0 to -1 but this rather makes the shakes stronger.

Removing the splitter solves the problem completely and the car runs super smooth without it.

I am running 550/275 springs, MCS Vorshlag coilovers, Boss ABS module, 2011 stock steering rack, stock front bushings, rear bushings are all spherical accept for the Dif.

The camera arm on the rear window exaggerates the motion quite a bit. It`s not as bad but the car still shakes quite bad at 100-140mph:



Mount a camera under the car behind the splitter and pointed toward it. I’d be curious to see if the splitter is buffering, or if it’s the belly/radiator pan.
 

Grant 302

basic and well known psychic
The splitter is on the heavier side and really stiff. Connected to the bumper cover and with rods to the bumper support beam in the front. There is no support to the chassis under the car yet as the splitter is not long enough.

Since your splitter seems like it might be stiffer than your mounting, it seems possible that it is fluttering and the mounting needs to be stiffened to eliminate.

^ Gonna go with this. Amplitude worsens with speed so the movement relative to the body needs to be restrained/damped or eliminated. I'd try supporting a few places at the back edge where it is and/or adding two rods at the front corners. Seems like the movement may be rotational or roll axis.

I know from my splitter (ABS material by 101blur) pics that the corners have a tendency to flex and move. I think that's the most important motion to restrain on your setup.

Good luck with the fix.
 
I am working on closing off and smoothing the airflow to the rear diffuser, I made an extension to the Verus diffuser and am working my way forward, I have the panels cut and bent to make the "frame rails" to the rockers a flat floor (Grey Panels in Picture), I hope to install them this weekend. I am wondering about making a piece to fill in under the trans and between the exhaust (Yellow Panel in Picture). I am thinking if I close in this area I would add some NACA ducts and some 4" tubing to get fresh air to the trans tunnel and rear end. I can also close off the exhaust piping path to shield the under car from heat transfer from the exhaust. I am wondering if it is worth the effort for the piece under the trans as it will make the maintenance a bit more complicated since it will likely need to be removed to do oil changes and trans fluid changes. I am also not sure what to do about the air from the front wheel wells that is going to come under the car from the area where the front sub-frame meets the body, should I try and seal that air out or encourage it to flow under the car? It is air that is well past the end of the splitter and could contribute to the airflow over the diffuser.

I am not an aerodynamicist and am really just winging it at this point.

Any thoughts?

Dave

IMG_6662.JPGIMG_6675.JPGIMG_6665.JPGUnder tray panels-small.jpg
 

Grant 302

basic and well known psychic
I'd worry about the part shown in yellow blocking too much cooling flow. I saw the vents in the @ track pic thread, but I think/suspect that's not enough area for all the air exiting the engine bay. I like the look of the paneling and the one you built for the rear axle should help, but I'm not sure the proposed additions are worth much downforce or drag reduction.
 
Where's your diff cooler mounted? If in the rear how is the airflow getting to it?
 
Diff cooler is between the diffuser and the trunk floor, I ran this setup on the last car and last weekend at Autobahn on this car without issue. It is a large cooler with a 10" electric fan. The pump comes on at 160* and the fan comes on at 180*. At the track about mid session the pump comes on and the fan cycles on and off over the last half of a 25min session. Peak diff temps are 202*. This number will rise at higher speed tracks but at Road America the peak temps where 219*.

I am fine with those numbers with a synthetic fluid in the diff. I also allow the car to cool in in the pits before shutting it down, if you do not you will get a temp spike in the diff that will raise to about 225* before it starts to cool down.

IMG_6652.JPG
 
I'd worry about the part shown in yellow blocking too much cooling flow. I saw the vents in the @ track pic thread, but I think/suspect that's not enough area for all the air exiting the engine bay. I like the look of the paneling and the one you built for the rear axle should help, but I'm not sure the proposed additions are worth much downforce or drag reduction.


Couldn't he add a naca duct to point air right where he wants it to go (the tranny)? If it's already low pressure air; not sure how much he'll get out of it, but perhaps it can be more "focused" air rather than turbulent chaos flowing over the tranny.

I'll also echo the point made that S550s look very tidy underneath out of the box
 

Grant 302

basic and well known psychic
Couldn't he add a naca duct to point air right where he wants it to go (the tranny)? If it's already low pressure air; not sure how much he'll get out of it, but perhaps it can be more "focused" air rather than turbulent chaos flowing over the tranny.
To make the duct, which isn't a 2D hole, you'd still pinch off even more flow escaping the engine bay. And there's really no room above the 'floor' level for the duct body/recess. Regardless of the hood venting, most engine bay cooling air still needs to exit this way. This is why the Laguna Sea used a scoop, IMO.

I'll also echo the point made that S550s look very tidy underneath out of the box
I agree for most of the underbody ahead of the front axle
This is a '15 and I don't see anything covering behind the K member around the tranny
15667940349_e406c68cab_o.jpg
 
Ahh interesting. For some reason I thought it was much smoother after of the k-member. The "up-kick" mentioned in the GT350 example is along the lines of what I was thinking. Less downforce, yes, but that goes for every inlet on the front end as well. Cooling drag is a necessary evil.
 
Added the side panels, still have to remove them and convert the self tapping tech screws to nutserts and powder coat the panels. I think I will run them as is at Road America next weekend and see if there is any complication before spending the energy on finishing the panels. I do not know how effective they will be but the weight added is minimal as the panels are very light aluminum.

Its hard to photograph but the center trans cover panel will not limit airflow and may actually help to extract air from the engine compartment by managing the airflow better under the car. even with the center panel in place there are still two large air paths along the sides of the engine block and rear mounting points of the K member. those two openings alone are about double the size of the grill openings in the front bumper. There is clear open lines from the radiator to the openings so airflow is not impeded by a bunch of obstacles. I am undecided about the center panel but will give it some more thought after next weekend.
IMG_6739.JPGIMG_6740.JPGIMG_6741.JPG

Someone also asked about the diffuser limiting airflow to the diff cooler, so here is a pic showing the available space, the main thing is the cooler is fan cooled so it does not need a direct air flow source to cool the cooler but you do not want it to recycle the same air over and over.
IMG_6747.JPG

Dave
 

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