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Ask AJ Hartman - Aero Questions

6
15
Exp. Type
Autocross
Exp. Level
Under 3 Years
Concord NC
AJ,
I'm new here but have watched many of your You Tube videos and want to talk with you and get some advice.

I have a 93 Notchback 4 cylinder car I'm currently doing HPDE events in NASA with but I am slowly building toward SCCA Improved Touring B class. We only can do limited modifications and I want to maximize within the rules what I can do.

I have two questions and my first has to do with front plastic fender liners and I feel like question two will tie into these. We can remove the fender liners by rules but I'm wondering if this is a good idea. My thought is that it could either help get rid of or cause even more lift in the front. What is your thoughts and advice?

My second question is what is your advice on the following rule taken from the SCCA rule book for IT:
A front spoiler/air dam is permitted. It shall not protrude beyond the overall outline of the body when viewed from above perpendicular to the ground, or aft of the forward most part of the front fender opening. This body outline does not include bumpers or bumper mounts. The spoiler/air dam shall be mounted to the body, and may extend no higher than four (4) inches above the horizontal centerline of the front wheel hubs. It shall not cover the normal grille opening(s) at the front of the car. Openings are permitted for the purposes of ducting air to the brakes, cooler, and radiator. Dealer installed or limited production front/rear spoilers/air dams/wings are prohibited. The spoiler shall have no support or reinforcement extending aft of the forward most part of the front fender wheel opening. NOTE: Integrated bumper assemblies are defined as those designs where an external non-metallic bumper cover completely encloses the primary energy-absorbing bumper and where this cover could be installed in its normal position with the underlying bumper removed. On cars with integrated bumpers, the front spoiler or air dam may be attached to the bumper cover. Where an air dam/spoiler is used, two total openings may be cut in the front valance to allow the passage of up to a three (3) inch diameter duct leading to each front brake/rotor assembly. Where no air dam/spoiler is used, two total openings of a maximum size five (5) inches by seven (7) inches maybe cut in the front valance so that brake ducts can be added with a three (3) inch diameter hose leading to each front brake/rotor assembly.

For question two what would you do to help the car within rules?
 
AJ,
I'm new here but have watched many of your You Tube videos and want to talk with you and get some advice.

I have a 93 Notchback 4 cylinder car I'm currently doing HPDE events in NASA with but I am slowly building toward SCCA Improved Touring B class. We only can do limited modifications and I want to maximize within the rules what I can do.

I have two questions and my first has to do with front plastic fender liners and I feel like question two will tie into these. We can remove the fender liners by rules but I'm wondering if this is a good idea. My thought is that it could either help get rid of or cause even more lift in the front. What is your thoughts and advice?

My second question is what is your advice on the following rule taken from the SCCA rule book for IT:
A front spoiler/air dam is permitted. It shall not protrude beyond the overall outline of the body when viewed from above perpendicular to the ground, or aft of the forward most part of the front fender opening. This body outline does not include bumpers or bumper mounts. The spoiler/air dam shall be mounted to the body, and may extend no higher than four (4) inches above the horizontal centerline of the front wheel hubs. It shall not cover the normal grille opening(s) at the front of the car. Openings are permitted for the purposes of ducting air to the brakes, cooler, and radiator. Dealer installed or limited production front/rear spoilers/air dams/wings are prohibited. The spoiler shall have no support or reinforcement extending aft of the forward most part of the front fender wheel opening. NOTE: Integrated bumper assemblies are defined as those designs where an external non-metallic bumper cover completely encloses the primary energy-absorbing bumper and where this cover could be installed in its normal position with the underlying bumper removed. On cars with integrated bumpers, the front spoiler or air dam may be attached to the bumper cover. Where an air dam/spoiler is used, two total openings may be cut in the front valance to allow the passage of up to a three (3) inch diameter duct leading to each front brake/rotor assembly. Where no air dam/spoiler is used, two total openings of a maximum size five (5) inches by seven (7) inches maybe cut in the front valance so that brake ducts can be added with a three (3) inch diameter hose leading to each front brake/rotor assembly.

For question two what would you do to help the car within rules?
Q1. Most people ditch the plastic fender liners. But at the same time, a lot of high end cars put a lot of effort into smoothing out the wheel wells to help airflow extraction, but thats all working as part of a system with a splitter with tunnels and a lot more going on. But thats not what the fender liners were designed on your car to do, so I would lean towards ditching them, unless you put your air filter in the fender well. I've seen people run into issues during rain races when the filter is in the fender well and not covered at all. Some of the air that makes it through the radiator will exit the wheel wells so removing them could actually help cooling.
Q2. SCCA has "unfun" aero rules. But it seems to say you are allowed a flat splitter where no part can be higher than 4 inches with a defined perimeter. So put the leading edge at 3" or so with a little rake up as you go rearward. That seems to be all you can do really, unless you really wanted to be a wordsmith in you interpretation of the rules. If I were you, go to a race and see what the front running guys do.
 
6
15
Exp. Type
Autocross
Exp. Level
Under 3 Years
Concord NC
Q1. Most people ditch the plastic fender liners. But at the same time, a lot of high end cars put a lot of effort into smoothing out the wheel wells to help airflow extraction, but thats all working as part of a system with a splitter with tunnels and a lot more going on. But thats not what the fender liners were designed on your car to do, so I would lean towards ditching them, unless you put your air filter in the fender well. I've seen people run into issues during rain races when the filter is in the fender well and not covered at all. Some of the air that makes it through the radiator will exit the wheel wells so removing them could actually help cooling.
Q2. SCCA has "unfun" aero rules. But it seems to say you are allowed a flat splitter where no part can be higher than 4 inches with a defined perimeter. So put the leading edge at 3" or so with a little rake up as you go rearward. That seems to be all you can do really, unless you really wanted to be a wordsmith in you interpretation of the rules. If I were you, go to a race and see what the front running guys do.
AJ, Thanks for the help and advice. I actually have the liners out now working on a few things so I'll just leave them out and I'll work on the splitter in the coming weeks . Kind of have my hands strapped but the fender liner advice makes since and as I was looking at the car I wondered about the wheel wells being an exit point if the liners were left out
 
4,621
4,533
Exp. Type
W2W Racing
Exp. Level
20+ Years
Pleasanton: 1/2 way between Sonoma and Laguna Seca
AJ, what do you think of this... Can you see useful applications for non class restricted mustangs? Wondering whether this system is all positives or whether there are important trade-offs (besides reliability concerns) https://www.google.com/url?sa=t&sou...MQFnoECCUQAQ&usg=AOvVaw1SZAwd4EvLhuoNu-UW5SEM

View attachment 67666
It’s effective. I believe some of the chapparels have movable wings back in the can am days. They would flatten out on the straights and pivot forward for braking. Most every racing sanction these days will specify “no movable aerodynamic devices” in the rules. At one time Sprint cars also had movable wings though I’m not sure if that’s still the case..
 

xr7

TMO Addict?
456
460
Exp. Type
Autocross
Exp. Level
5-10 Years
Minnesota
It’s effective. I believe some of the chapparels have movable wings back in the can am days. They would flatten out on the straights and pivot forward for braking. Most every racing sanction these days will specify “no movable aerodynamic devices” in the rules. At one time Sprint cars also had movable wings though I’m not sure if that’s still the case..
Your right about those Chapparels. I seem to recall some F1 cars also trying that. The other piece I recall was some had the wings mounted directly to the suspension uprights so the down force was applied directly to the tire. Lastly if the old flux capacitor memory is correct the F1's had a bad habit of these wings collapsing.
 

Dave_W

Cones - not just for ice cream
450
449
Exp. Type
Autocross
Exp. Level
20+ Years
Connecticut
1955 Le Mans Mercedes 300SLR
Actuated by a hydraulic ram using engine oil pressurized by a gearbox-driven auxiliary pump. Deployed by the driver using a switch on the dash, and retracted either by the driver with the same switch or automatically by a switch on the gearshift gates. Not only did it just decelerate the car, but it acted as a spoiler to create pressure/downforce on the rear body to increase rear grip under braking and acceleration.
1629576086600.png © Getty Images
1629576286540.png
1629576332933.png

 

Mad Hatter

Gotta go Faster
4,100
2,645
Santiago, Chile
Cool ideas. My mecanic has been after me for a while about some kind of ram on the wing to change the angle. We loose about 8km/h on the straights from the wing. In for any enlightenment!!
 
Most series don't allow any movable aerodynamic device so I've personally never played with them. They are pretty complex to do properly, and the chance of something going wrong can have some disasterous results. If you set up your wing to be a DRS setup, and head into a brake zone and it stays open and you have way less rear Df, that can be really dangerous. Same with if its set up as an air brake. If you are pushing into a brake zone and it doesn't come up and you have much less braking (or slowing) performance, that won't be good either. If you like tinkering with stuff, I say go for it. Its neat for sure. I'm not gonna mess with anything cause like I mentioned above, isn't legal in most classes so wouldn't ever be able to sell anything from a business perspective.
 
62
34
Exp. Type
HPDE
Exp. Level
Under 3 Years
Cantley
Very good points, thanks for taking the time. I do like to tinker, but not as much as being on the track!
 
74
93
Exp. Type
HPDE
Exp. Level
Under 3 Years
Michigan
AJ, thanks for making this thread! I've been following you on Instagram for a while now, great stuff! I have some suspension and safety mods to make before I can start thinking about aero, but it's in the back of my mind.

My question is- how much difference does it make where the hood louvres are in fore/aft placement on the hood? The reason I ask is my new engine is really tall at the front and pokes out of the hood. I'm going to make a bump and glass it into the hood and wanted to put some heat extraction louvres in it as well.

Here's a photo of where the engine peeks out-
_J2_0151.jpg
This is before the hood was on it, but might give you an idea of where the tallest point falls.
_J2_0042-3.jpg
Thanks!
Brad
 
Last edited:

Grant 302

basic and well known psychic
74
93
Exp. Type
HPDE
Exp. Level
Under 3 Years
Michigan
I created/broke this out when I was a mod. Glad that it could help people, even if I got scolded a bit for doing this. 😆

People who want AJH’s opinion should have access to it. :idontknow:
Oh, okay! Well, I appreciate it, haha!

didt know this was a forum topic to join in on
Hello, Frank! I'm following you on Instagram as well.

I read 'Ask AJ Hartman- Aero Questions'...and assumed AJ started it so we could ask aero questions. Apologies if I misunderstood the point of the thread.

Brad
 
AJ, thanks for making this thread! I've been following you on Instagram for a while now, great stuff! I have some suspension and safety mods to make before I can start thinking about aero, but it's in the back of my mind.

My question is- how much difference does it make where the hood louvres are in fore/aft placement on the hood? The reason I ask is my new engine is really tall at the front and pokes out of the hood. I'm going to make a bump and glass it into the hood and wanted to put some heat extraction louvres in it as well.

Here's a photo of where the engine peeks out-
View attachment 69839
This is before the hood was on it, but might give you an idea of where the tallest point falls.
View attachment 69840
Thanks!
Brad
Its a little hard to tell but I'd look at adding louvers to the "high" part of the hood (effectively cut out the low area up to the body line) and completely skip trying to make your own fiberglass bubble. This will give you decent volume. I know you kinda asked about louver placement and that would keep you from going to far rearward for sure. Figure out where your radiator is and start to louver right at that. Not sure if you saw all my wind tunnel videos but the guys over at Race Louvers make really nice ones and have all sorts of sizes so could find something that would plop right on.
 
74
93
Exp. Type
HPDE
Exp. Level
Under 3 Years
Michigan
Its a little hard to tell but I'd look at adding louvers to the "high" part of the hood (effectively cut out the low area up to the body line) and completely skip trying to make your own fiberglass bubble. This will give you decent volume. I know you kinda asked about louver placement and that would keep you from going to far rearward for sure. Figure out where your radiator is and start to louver right at that. Not sure if you saw all my wind tunnel videos but the guys over at Race Louvers make really nice ones and have all sorts of sizes so could find something that would plop right on.
Ahhhh, that's an excellent idea! Thanks AJ. I'll check them out.

Thanks!

Brad
 

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