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Let's Talk Aero

32
48
Exp. Type
HPDE
Exp. Level
Under 3 Years
Nashville TN
For those of us balancing street and track (or, more specifically, for me :)):

I'm currently running the GT350R splitter, a GT4 center hood vent, and the stock swing + gurney flap. I'm looking at perhaps adding the Verus full diffuser (not the add-on strakes). Anybody running a similar combo and have thoughts on the balance thereof? I ran the existing combo at Memphis hitting near 150mph and didn't have issues with balance, so I would think the diffuser would add some rear grip and perhaps some push.

My thought is, as compared to a stock GT350R, I have a bit more front aero with the hood vent, and a bit less with the swing/gurney vs the R wing, so the diffuser might put the balance in line with the stock GT350R balance, which should be reasonable.
 
71
31
Exp. Type
HPDE
Exp. Level
5-10 Years
So CA
PP2 has a 'spoiler', not a 'wing'. It makes some downforce unlike the 'wing'. Not a ton, but better than the PP1 wing.
Bringing this back, not looking for crazy aero at this point for baselines but anyone know if adding the GT350 taller spoiler helps and by how much, vs the stock PP2? I’m about to track at Auto Club Speedway, high banking Roval config. Thx!
 
Bringing this back, not looking for crazy aero at this point for baselines but anyone know if adding the GT350 taller spoiler helps and by how much, vs the stock PP2? I’m about to track at Auto Club Speedway, high banking Roval config. Thx!
We have a number on the 350R wing to no wing and the effect on the rear wheels was only about 125lbs at 100mph. We did do a 1" and 3" spoiler test and the 3" spoiler was surprisingly close to the 350R wing. We didn't have a swing to test but Looking at the design, the Swing would probably perform under that of the R wing, so going from a PP2 spoiler, to the GT350 swing, the delta may be in the 50-75lb range at 100mph.
 
71
31
Exp. Type
HPDE
Exp. Level
5-10 Years
So CA
We have a number on the 350R wing to no wing and the effect on the rear wheels was only about 125lbs at 100mph. We did do a 1" and 3" spoiler test and the 3" spoiler was surprisingly close to the 350R wing. We didn't have a swing to test but Looking at the design, the Swing would probably perform under that of the R wing, so going from a PP2 spoiler, to the GT350 swing, the delta may be in the 50-75lb range at 100mph.
Great info, thanks! I’ll get the feel of it this weekend at the Roval.
 
114
84
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
We did do a 1" and 3" spoiler test and the 3" spoiler was surprisingly close to the 350R wing.

Were you *really* surprised or just a little disappointed? Spoilers are powerful and, at least for the first 'X' height, they're also (usually) reasonably clean because they tend to help clean up a little of the separation off the roofline and organize the flow coming from under the car. I bet if you're really trying to crank some AoA into a rear wing, having some sort of spoiler to help turn the underside flow would be a real advantage. In other applications, I've found this interaction to be quite strong.
 

Grant 302

basic and well known psychic
Were you *really* surprised or just a little disappointed? Spoilers are powerful and, at least for the first 'X' height, they're also (usually) reasonably clean because they tend to help clean up a little of the separation off the roofline and organize the flow coming from under the car. I bet if you're really trying to crank some AoA into a rear wing, having some sort of spoiler to help turn the underside flow would be a real advantage. In other applications, I've found this interaction to be quite strong.
Lol.
 
318
319
Exp. Type
W2W Racing
Exp. Level
20+ Years
Snowy North
Andy Pilgrim did a 350 vs 350R comparo at NCMP for Automobile (online) Mag a coupla years ago.

IIRC...Andy said that Ford told him the d'force from the 350 swing+ g-flap was 20 or 30# less than the 350R wing...above 100mph.

Hmmmm...gotta go find that one again. It was a fun episode.

UPDATE: Swing delivers 180# vs 140# for 350R full [email protected] 120mph. Ask Andy for his reference data...not me lol.
 
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Andy Pilgrim did a 350 vs 350R comparo at NCMP for Automobile (online) Mag a coupla years ago.

IIRC...Andy said that Ford told him the d'force from the 350 swing+ g-flap was 20 or 30# less than the 350R wing...above 100mph.

Hmmmm...gotta go find that one again. It was a fun episode.
Actually there is an article saying the swing with gurney generates 379lbs at 180mph.

So at 100 is basically like the 350R.
But much more drag (IMO)
 
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114
84
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
Flyhalf, have you introduced much pitch sensitivity with your splitter work? I don't know what kind of ride heights you're running, but I don't think you have a raised center on that splitter? I'm just curious if it's ever an issue.
 
Flyhalf, have you introduced much pitch sensitivity with your splitter work? I don't know what kind of ride heights you're running, but I don't think you have a raised center on that splitter? I'm just curious if it's ever an issue.
I have a 1-2 deg pitch. Just regular flat blade. I could have more but now sure worth it without tunnels.
With the new one that im making with AJ tunnels that i might play a little more with it.
Height of splitter is 2.75 -3"
Height
 
114
84
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
I have a 1-2 deg pitch. Just regular flat blade. I could have more but now sure worth it without tunnels.
With the new one that im making with AJ tunnels that i might play a little more with it.
Height of splitter is 2.75 -3"
Height

I don't think I asked my question correctly. I wasn't asking about the splitter itself.

On track, do you feel an increase in the pitch sensitivity of the entire car? When you're on the brakes with the nose down and the tail up, do you get to a point where either downforce of the splitter gets very high and creates corner entry oversteer or restricts flow under the car causing a big wash?
 
I don't think I asked my question correctly. I wasn't asking about the splitter itself.

On track, do you feel an increase in the pitch sensitivity of the entire car? When you're on the brakes with the nose down and the tail up, do you get to a point where either downforce of the splitter gets very high and creates corner entry oversteer or restricts flow under the car causing a big wash?
That would be called porpoising. Its pretty crazy when it happens. I'll let flyhalf answer his own experiences, but generally it happens when the splitter itself isn't strong enough and thats what flops up and down. If the splitter is much stiffer, and the chassis starts porpoising, its very pronounced. I've had this happen. Pitch sensitivity is an issue for sure, but at the Df levels of the average track car, and no flat bottom, a raised center splitter is pretty pointless.
 
Were you *really* surprised or just a little disappointed? Spoilers are powerful and, at least for the first 'X' height, they're also (usually) reasonably clean because they tend to help clean up a little of the separation off the roofline and organize the flow coming from under the car. I bet if you're really trying to crank some AoA into a rear wing, having some sort of spoiler to help turn the underside flow would be a real advantage. In other applications, I've found this interaction to be quite strong.
Surprised. I would have been disappointed if the 3" spoiler almost matched my wing haha. It was a combo of the R wing being worse than I thought, and the 3" spoiler being a little better than I thought. I should also clarify that those spoiler tests were done alone. Not with our wing on the car. We did do a 1" spoiler on the 98 Mustang in the wind tunnel in conjunction with our wing and it wasn't that efficient of a gain, and with plenty of room to go up on the wing, wouldn't recommend it on that situation, but I'm sure theres setups or situations where it is may be a good option.
 
I don't think I asked my question correctly. I wasn't asking about the splitter itself.

On track, do you feel an increase in the pitch sensitivity of the entire car? When you're on the brakes with the nose down and the tail up, do you get to a point where either downforce of the splitter gets very high and creates corner entry oversteer or restricts flow under the car causing a big wash?
One of the thing I've learned in this my adventure is the word BALANCE.
more than the absolute max DF rear or front.
I knew roughly what a plain blade splitter can do and i tried to match it with the angle of the wing.
Now going up in front DF is justified because the better rear wing (from apr250 to AJ fulcrum 14)
I base my assumptions on data avaialble and conversations with expert people like AJ etc.
I had for few events the car tending to get light on the rear in braking zone.
I doubt that at 80-100 braking and turn the increasing pitch due to DF was the reason of that behavior (and tendency of oversteering)
At those speeds it is more suspension related and weight distribution.
Rebound and compression were also just wrong in the rear. And so was front compression.
Not considering that maybe I'm on the lighter side of the springs (i run cortex JRi DA btw)
But
In this pic you see t1 of daytona.
Where i was coming from 170 with a long trail braking.
You can notice how flat is the rear wing (too much but i just wanted to send it lol )
At that speed with a tire blocker and a 6" lip and blade splitter you probably generating 500+lbs of Df. While the rear wing is around 300. (Maybe...)
The suspension are perfectly dial in here so is more aero related. (I should have increase slighlty the spring rate with those speed but i didn't)
I never had the issue in straight line.
I do run sliders under to avoid a complete seal of the splitter with the ground.


I feel the car is balanced and with increasing of DF i believe i will go up with spring rate too (there is a nice video of AJ explaining how roughly calculate the right spring rate)

Hope this answer some of the question :)

received_225099226469303~2.jpeg
 
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I don't think I asked my question correctly. I wasn't asking about the splitter itself.

On track, do you feel an increase in the pitch sensitivity of the entire car? When you're on the brakes with the nose down and the tail up, do you get to a point where either downforce of the splitter gets very high and creates corner entry oversteer or restricts flow under the car causing a big wash?

Here the example of unbalance car with too much diff between front and rear with rear going away at 125mph.
 
114
84
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
Surprised. I would have been disappointed if the 3" spoiler almost matched my wing haha. It was a combo of the R wing being worse than I thought, and the 3" spoiler being a little better than I thought. I should also clarify that those spoiler tests were done alone. Not with our wing on the car. We did do a 1" spoiler on the 98 Mustang in the wind tunnel in conjunction with our wing and it wasn't that efficient of a gain, and with plenty of room to go up on the wing, wouldn't recommend it on that situation, but I'm sure theres setups or situations where it is may be a good option.

I just remember with the original CoT, the stock car guys were making a lot of noise about the wing being less downforce than the spoiler. I'm sure NASCAR made the rules to produce that outcome, but it didn't take that long to return to the spoiler.

Nightmare Moon has run the 10" tall AutoX spoiler and says it really sticks the back of the car. No doubt, it's dirty as hell aerodynamically, but it makes the watch go in the right direction on a fast parking lot course or slow track. The CAM rules allow for a 6" splitter for balance. No aftermarket wings are allowed.

My questions were not about propoising. If flyhalf didn't have that at Daytona, then he won't have it. I was describing a situation where the front of the car gets either 'pinned' by being very close to the ground and extra powerful or 'no one home' because the splitter is on the ground and the flow underneath has been blocked. Judging by what you both have said, these cars just don't run in the ride height range which would induce these behaviors.
 
I just remember with the original CoT, the stock car guys were making a lot of noise about the wing being less downforce than the spoiler. I'm sure NASCAR made the rules to produce that outcome, but it didn't take that long to return to the spoiler.

Nightmare Moon has run the 10" tall AutoX spoiler and says it really sticks the back of the car. No doubt, it's dirty as hell aerodynamically, but it makes the watch go in the right direction on a fast parking lot course or slow track. The CAM rules allow for a 6" splitter for balance. No aftermarket wings are allowed.

My questions were not about propoising. If flyhalf didn't have that at Daytona, then he won't have it. I was describing a situation where the front of the car gets either 'pinned' by being very close to the ground and extra powerful or 'no one home' because the splitter is on the ground and the flow underneath has been blocked. Judging by what you both have said, these cars just don't run in the ride height range which would induce these behaviors.
I think the issue with a wing that close to the trunk is the low pressure on the bottom surface of the wing a few inches away from the trunk gets canceled out a bit.

I'm not familiar with nightmare moon but sounds like hes maxing out the rules hes allowed. Spoilers for sure work. But they are nowhere near what I'll call a proper wing in an advantageous position can do, but again, you have to work in the rules you are building to.

And I get what you are saying now. I know flyhalf didn't have that issue per se, but his splitter did buckle in the middle where there wasn't any support. If your splitter slams down to the ground and seals off and doesn't pop back up, either your springs are much to soft, your anti dive geometry is absolute crap, or your splitter is not nearly as effective as it could be. Or a combo of all of them. I actually run my car so it hits a hard bump stop on the shocks since I'm so aero heavy to prevent my splitter from bottoming out. And with 900lb springs on the front, if the splitter seals off, the front of the car will definitely bounce up. The car was undriveable until I got the setup right for my case.
 

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