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Factory Fender Vents in ST4


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  • 3 weeks later...
On 8/20/2020 at 1:35 AM, Greg G. said:

No. 6.4.2. 

Hi Greg - if the factory fender vents are not allowed, is there anything that a competitor with a Lotus Exige can do to be compliant?  Would blocking/taping the vents suffice, or would that car need to be classed in ST3 and above?  

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There are many cars with factory fender vents as part of their BTM aero package.

e46 and newer m3


c5 and newer Corvette


Civic type R



If these OEM fenders are illegal while taking BTM in ST3, or with or without taking BTM in ST4-6, then there are many illegal cars out there competing this weekend.

Please clarify.

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  • National Staff

If the Base Trim Model has factory vents, then there does not appear to be a rule preventing them.  But, if it is not the base trim model, and the BTM does not have them, then the only modification to fenders permitted is this:

Rolled or flared fenders (includes add-on flares--only to the extent necessary
to cover the tire as viewed from above—not viewed from the front or rear)

In the OP's question above, the vents are from an Exige S, which is not BTM. 

The E46 is in Appendix B, as are the C5 Z06 and C6 Grand Sport, so they are considered BTM (but cannot have a wing/rear spoiler or rear diffuser still).

I've seen photos of RX-8's without vents--not sure if it was a year of manufacture issue or an upgrade/option issue.

The Civic Type R has all kinds of Aero issues that would prevent it from the BTM Aero Mod Factor, and as well, may prevent it from being an ST4 vehicle.


To the OP: Yes, if you were to cover the vents, I don't think anyone would protest you for them.

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  • 10 months later...

It interesting to me that M3s and Corvettes are able to have "OEM" fender Vents. However,  from the Original Manufacture they are actually not fully functional as fender vents due to the factory fender lines and the Trim pieces, both things people remove to make them functional. Due to this, the rules allow higher level trim models to basically  have fender vents by removing OE parts. Which is technically a modification. By that those vehicle owners gain an advantage over others cars. It has been proven that Fender vents are one of the best mods to reduce drag and increase down force. So how is it fair that some cars in ST4 get it and others dont?

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