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Howdy SCCA TT Rules Board Members!
Today we ask for your attention on a matter within the aero rules limitations in SCCA Time Trials Max category, namely the front splitter rules - which seem to be a bit cramped for some of the "big" modern cars, and also don't mesh well with some OEM solutions.
THE STRUGGLE: MAKING FRONT DOWNFORCE
I am asking about these rules as our shop delves into two Max category splitter and wing installations on the two cars below, which we need to complete over the next handful of weeks - with one of these cars is going to SCCA TT Nationals.
The white 2020 Shelby GT350 is a customer's car that going from SCCA S2 to M2 class prep, with coilovers, a splitter and wing. My black-ish 2015 Mustang GT is already in M1 but has no aero mods - yet - and I am hesitant to put a very "low effectiveness" splitter onto my somewhat radical but otherwise M1 legal build. I figured it couldn't hurt to ask...
We are familiar with adding aero to autocross and road race cars, but somewhat new to the SCCA Max ruleset. What we have found in road course use is that it is always RELATIVELY EASY to make rear downforce (with a wing that fits the Max rules alone, much less with the addition of a rear diffuser) but to keep the aero balance front-to-rear correct, the struggle is on the front with a "sedan shaped car".
We tend to correct for this in 2 ways: we make very large front splitters (sometimes 10-12" extended from the front bumper cover) and then utilize hood ducting to help get front aero balance to match the rear. These big splitters would all fall well outside of the limits of Max category, which are stuck at 5" extension, then limited again with tiny tunnels (exception: the optional XS/CAM rules, which I will talk about below).
Making massive hood ducting is fun to do, and it really works to increase front downforce, but it takes VERY expensive fabrication to create. The front duct work on the car above gobbled up 200+ man hours, only a fraction of which can be seen from the outside (the rest is hidden, below right).
We have tackled this ducted hood work on several cars, and it is always a lot of work. The current Max rules do not preclude racers from doing this, and with an engineering eye towards directing airflow through the lower grill opening right over the splitter, then out through these massive hood ducts, you CAN make much more downforce this way. But it is crushingly expensive to do this.
We don't think that this level of work should be the only way to get good front downforce in a big car like this, especially when the splitter length is so limited. But if we have to - we will.
A much less costly way to add more front downforce, which has really come out for the grassroots racer in the last few years, are splitter ramps / diffusers / tunnels. This is a much more cost effective way to get that balance, but the current Max ruleset is making this a real challenge.
SPLITTER RAMP SIZE MATTERS
When you are already going to the expense to make a custom splitter (which Max allows), adding a "large" pair of splitter ramps doesn't cost much if any more than a "small" set of splitter ramps.
The Cadillac CTS-V above was fitted with a plywood splitter and a pair of these carbon fiber tunnels from Professional Awesome. This $300 pair of relatively small tunnels (72 sq in each) were angled and aimed at the brakes to not only give us more front downforce but could also direct air towards brake cooling deflectors pointing at the hubs and rotors, to keep them cool.
Like many companies, ProA make splitter ramps in differing sizes, but the costs are not all that different from large to small. Their 12x6" carbon splitters are $300/pair, but their larger plastic ramps (shown above right and below) are also $300/pair. So there is no real cost savings going with their smaller ramps...
On a big car like this EVO X above, the larger ProA ramps fit great and help this big car get some much needed front downforce.
But on a smaller / lighter car like a Miata that larger splitter ramp size would seem enormous. The EVO is 3600 pounds and much wider than the 2200 pound Miata, so while it can have a WIDER splitter (based on the body limits in the rules) the bigger car cannot use a splitter that is any LONGER, plus is limited to the same total surface size in splitter ramps as the tiny Miata. Yet with engine swaps and turbo additions they can often be run side by side in the same class. We have a solution to this dilemma, below.
THE MAX SPLITTER RULES
In the 2023 Max rules the wing limits are pretty enormous (essentially unlimited), but the splitter rules seem very conservative, especially for the bigger / heavier cars. All Max prep cars can have a huge wing (with CAM / XS rules limited to 8 sq ft surface area), no matter the car's size and weight. Add in the optional diffuser and Max cars we can have all of the rear downforce we ever wanted but the front is very limited, especially on the big cars. The limited front downforce allowances that exist simply do not scale up with car size.
The red text above would denote a recent change, with max surface area for the tunnels called out. But the square inch limit (2 tunnels of 84 sq inches each) is pretty low. Here are some examples of off-the-shelf splitter tunnels (aka:" ramps" or "diffusers"):
The large ProA ramp above left, which is "normal" ramp for a big / heavy car like the Mustang, is 177 sq inches. The small ramps above right are 72 sq inches, and when ordered in carbon from this shop they are exact same price as the large version. This EVO shown above has a pair of these large ProA ramps and we have trial fitted them to our own big heavy Mustang and they look like a perfect fit. Now on a Miata the 72 sq in ramp would seem plenty big.
OEM UNDERTRAY - SOME HAVE BIG RAMPS
As we were contemplating the rules this week for these two Mustangs, we took some measurements of a modern pony car's factory front undertray, the 2020 Shelby GT350 Mustang. It has four splitter ramps which we measured manually as well as with pictures + scaling, then imported that into SolidWorks for an accurate area measurement.
The stock undertray has 4 ramps totaling 339 sq inches, which is nearly double what the Max rules allow (84 x 2 = 168 sq in). As you will see above and below, we also marked the front axle centerline - with two of the factory ramps behind that. That is also to show that the other splitter "hard limit" (not to extend behind the front axle centerline) is also not fitting within OEM offerings. The GT350 was introduced in 2015 (the 2016 model year), fully 8 years ago.
The undertray extends back to the transmission interface on this car, 10.5" behind the front axle centerline. That makes for some potential "model imbalance" based on OEM fitments for some models. How do we make a Max legal splitter for this car while also not losing what the OEM undertray gives us? Shouldn't the Max rules include what a commonly raced OEM car has?
Other than the 200TW tire limit, Max category is home to some pretty radical builds and allowances. Modifications such as the 7.4L GM engine we swapped into our Mustang is allowed in both Max1 and CAM-C, but we have to use a splitter that seems like it was made for a tiny Miata - the 5" extension is small, as are the splitter ramps we are seemingly limited to.
CAM / XS RULES EXEMPTION
All of this gets thrown out on its ear when you look at this giant loophole built into the Max rule book:
This allowance lets virtually any car pick the more liberal aero limits within CAM or XS, shown below. We cannot find a downside to doing this for either of these two cars - it is all upside.
Not only does CAM / XS allow for a longer 6" extension past the front bumper, they do not list ANY limits on splitter tunnels. And I know for a fact many of the current CAM cars do have splitters with ramps.
Then that last bit that is circled would seemingly allow ANY splitter / diffuser / wing to be legal, as long as it was commercially available. So... a shop like ours could make something completely out of the realm of the Max or CAM/XS rules, slap it on our website, and it would be legal - until ruled upon.
While we do run CAM-C for autocrossing, and planned this whole season around running their ruleset, that seems like a weird way to skirt the Max limitations.
RULES PROPOSAL TO FIX ALL THIS?
How would we square this circle? With a few small tweaks to the Max aero rules, I suspect most competitors would build around the Max rules instead of taking the CAM / XS alternate ruleset of even trying to torture the CAM / XS "commercially available exemption". Here are three proposed rules changes:
1. Allow the same 6" splitter extension in Max that CAM / XS allows in Max. (That one is easy)
2. Possibly update the splitter length rearward to "front axle centerline or as far back as the OEM front undertray assembly". (not a huge concern just a bit of a glaring omission)
Third, and most important in our eyes, is to allow a scaled splitter ramp size. Tie the total splitter ramp surface area limit to something that ties into the car's size & weight. The easiest metric we can come up with is this:
3. Splitter tunnels are limited to the following surface area maximums based on factory wheelbase:
Then maybe you folks could encourage the CAM rules making body to drop that "commercially available" loophole. It s Pandora's box ready to be opened.
We have numerous local racers asking us to make their splitter and wing setups for SCCA TT use, but we just want to make sure the rules are both equalized for the big cars and stable before we tackle any of this work. But we don't have much time before we have to finish some of these cars, as Bowling Green is calling to us in October...
Thanks for reading,
Terry Fair and the crew at Vorshlag Motorsports
Race car business owner and SCCA TT competitor
Today we ask for your attention on a matter within the aero rules limitations in SCCA Time Trials Max category, namely the front splitter rules - which seem to be a bit cramped for some of the "big" modern cars, and also don't mesh well with some OEM solutions.
THE STRUGGLE: MAKING FRONT DOWNFORCE
I am asking about these rules as our shop delves into two Max category splitter and wing installations on the two cars below, which we need to complete over the next handful of weeks - with one of these cars is going to SCCA TT Nationals.
The white 2020 Shelby GT350 is a customer's car that going from SCCA S2 to M2 class prep, with coilovers, a splitter and wing. My black-ish 2015 Mustang GT is already in M1 but has no aero mods - yet - and I am hesitant to put a very "low effectiveness" splitter onto my somewhat radical but otherwise M1 legal build. I figured it couldn't hurt to ask...
We are familiar with adding aero to autocross and road race cars, but somewhat new to the SCCA Max ruleset. What we have found in road course use is that it is always RELATIVELY EASY to make rear downforce (with a wing that fits the Max rules alone, much less with the addition of a rear diffuser) but to keep the aero balance front-to-rear correct, the struggle is on the front with a "sedan shaped car".
We tend to correct for this in 2 ways: we make very large front splitters (sometimes 10-12" extended from the front bumper cover) and then utilize hood ducting to help get front aero balance to match the rear. These big splitters would all fall well outside of the limits of Max category, which are stuck at 5" extension, then limited again with tiny tunnels (exception: the optional XS/CAM rules, which I will talk about below).
Making massive hood ducting is fun to do, and it really works to increase front downforce, but it takes VERY expensive fabrication to create. The front duct work on the car above gobbled up 200+ man hours, only a fraction of which can be seen from the outside (the rest is hidden, below right).
We have tackled this ducted hood work on several cars, and it is always a lot of work. The current Max rules do not preclude racers from doing this, and with an engineering eye towards directing airflow through the lower grill opening right over the splitter, then out through these massive hood ducts, you CAN make much more downforce this way. But it is crushingly expensive to do this.
We don't think that this level of work should be the only way to get good front downforce in a big car like this, especially when the splitter length is so limited. But if we have to - we will.
A much less costly way to add more front downforce, which has really come out for the grassroots racer in the last few years, are splitter ramps / diffusers / tunnels. This is a much more cost effective way to get that balance, but the current Max ruleset is making this a real challenge.
SPLITTER RAMP SIZE MATTERS
When you are already going to the expense to make a custom splitter (which Max allows), adding a "large" pair of splitter ramps doesn't cost much if any more than a "small" set of splitter ramps.
The Cadillac CTS-V above was fitted with a plywood splitter and a pair of these carbon fiber tunnels from Professional Awesome. This $300 pair of relatively small tunnels (72 sq in each) were angled and aimed at the brakes to not only give us more front downforce but could also direct air towards brake cooling deflectors pointing at the hubs and rotors, to keep them cool.
Like many companies, ProA make splitter ramps in differing sizes, but the costs are not all that different from large to small. Their 12x6" carbon splitters are $300/pair, but their larger plastic ramps (shown above right and below) are also $300/pair. So there is no real cost savings going with their smaller ramps...
On a big car like this EVO X above, the larger ProA ramps fit great and help this big car get some much needed front downforce.
But on a smaller / lighter car like a Miata that larger splitter ramp size would seem enormous. The EVO is 3600 pounds and much wider than the 2200 pound Miata, so while it can have a WIDER splitter (based on the body limits in the rules) the bigger car cannot use a splitter that is any LONGER, plus is limited to the same total surface size in splitter ramps as the tiny Miata. Yet with engine swaps and turbo additions they can often be run side by side in the same class. We have a solution to this dilemma, below.
THE MAX SPLITTER RULES
In the 2023 Max rules the wing limits are pretty enormous (essentially unlimited), but the splitter rules seem very conservative, especially for the bigger / heavier cars. All Max prep cars can have a huge wing (with CAM / XS rules limited to 8 sq ft surface area), no matter the car's size and weight. Add in the optional diffuser and Max cars we can have all of the rear downforce we ever wanted but the front is very limited, especially on the big cars. The limited front downforce allowances that exist simply do not scale up with car size.
The red text above would denote a recent change, with max surface area for the tunnels called out. But the square inch limit (2 tunnels of 84 sq inches each) is pretty low. Here are some examples of off-the-shelf splitter tunnels (aka:" ramps" or "diffusers"):
The large ProA ramp above left, which is "normal" ramp for a big / heavy car like the Mustang, is 177 sq inches. The small ramps above right are 72 sq inches, and when ordered in carbon from this shop they are exact same price as the large version. This EVO shown above has a pair of these large ProA ramps and we have trial fitted them to our own big heavy Mustang and they look like a perfect fit. Now on a Miata the 72 sq in ramp would seem plenty big.
OEM UNDERTRAY - SOME HAVE BIG RAMPS
As we were contemplating the rules this week for these two Mustangs, we took some measurements of a modern pony car's factory front undertray, the 2020 Shelby GT350 Mustang. It has four splitter ramps which we measured manually as well as with pictures + scaling, then imported that into SolidWorks for an accurate area measurement.
The stock undertray has 4 ramps totaling 339 sq inches, which is nearly double what the Max rules allow (84 x 2 = 168 sq in). As you will see above and below, we also marked the front axle centerline - with two of the factory ramps behind that. That is also to show that the other splitter "hard limit" (not to extend behind the front axle centerline) is also not fitting within OEM offerings. The GT350 was introduced in 2015 (the 2016 model year), fully 8 years ago.
The undertray extends back to the transmission interface on this car, 10.5" behind the front axle centerline. That makes for some potential "model imbalance" based on OEM fitments for some models. How do we make a Max legal splitter for this car while also not losing what the OEM undertray gives us? Shouldn't the Max rules include what a commonly raced OEM car has?
Other than the 200TW tire limit, Max category is home to some pretty radical builds and allowances. Modifications such as the 7.4L GM engine we swapped into our Mustang is allowed in both Max1 and CAM-C, but we have to use a splitter that seems like it was made for a tiny Miata - the 5" extension is small, as are the splitter ramps we are seemingly limited to.
CAM / XS RULES EXEMPTION
All of this gets thrown out on its ear when you look at this giant loophole built into the Max rule book:
This allowance lets virtually any car pick the more liberal aero limits within CAM or XS, shown below. We cannot find a downside to doing this for either of these two cars - it is all upside.
Not only does CAM / XS allow for a longer 6" extension past the front bumper, they do not list ANY limits on splitter tunnels. And I know for a fact many of the current CAM cars do have splitters with ramps.
Then that last bit that is circled would seemingly allow ANY splitter / diffuser / wing to be legal, as long as it was commercially available. So... a shop like ours could make something completely out of the realm of the Max or CAM/XS rules, slap it on our website, and it would be legal - until ruled upon.
While we do run CAM-C for autocrossing, and planned this whole season around running their ruleset, that seems like a weird way to skirt the Max limitations.
RULES PROPOSAL TO FIX ALL THIS?
How would we square this circle? With a few small tweaks to the Max aero rules, I suspect most competitors would build around the Max rules instead of taking the CAM / XS alternate ruleset of even trying to torture the CAM / XS "commercially available exemption". Here are three proposed rules changes:
1. Allow the same 6" splitter extension in Max that CAM / XS allows in Max. (That one is easy)
2. Possibly update the splitter length rearward to "front axle centerline or as far back as the OEM front undertray assembly". (not a huge concern just a bit of a glaring omission)
Third, and most important in our eyes, is to allow a scaled splitter ramp size. Tie the total splitter ramp surface area limit to something that ties into the car's size & weight. The easiest metric we can come up with is this:
3. Splitter tunnels are limited to the following surface area maximums based on factory wheelbase:
- 90" and under wheelbase cars are limited to 168 sq inches total for up to 4 splitter ramps (current limit)
- 91-99" wheelbase cars are limited to 250 sq inches total for up to 4 splitter ramps
- 100"-up wheelbase cars are limited to 400 sq inches total for up to 4 splitter ramps
Then maybe you folks could encourage the CAM rules making body to drop that "commercially available" loophole. It s Pandora's box ready to be opened.
We have numerous local racers asking us to make their splitter and wing setups for SCCA TT use, but we just want to make sure the rules are both equalized for the big cars and stable before we tackle any of this work. But we don't have much time before we have to finish some of these cars, as Bowling Green is calling to us in October...
Thanks for reading,
Terry Fair and the crew at Vorshlag Motorsports
Race car business owner and SCCA TT competitor