ST4 BTM aero rules clarification for hood and bumper cooling mods

[codename Bil Doe]

Hi,

Rules 6.3.5 and 6.3.6 allow for alternate and modified hoods and front bumper fascia for cooling and weight reduction.

Does this apply also to the rear engine cover/lid on a rear mid engine car like a Fiero, 914, or Boxster? Venting the rear engine cover/lid has big effect on cooling.

How do those two BTM aero rules apply to rear mid cars like that?

Thanks

 

[Roman V.]

8 hours ago, codename Bil Doe said:

Hi,

Rules 6.3.5 and 6.3.6 allow for alternate and modified hoods and front bumper fascia for cooling and weight reduction.

Does this apply also to the rear engine cover/lid on a rear mid engine car like a Fiero, 914, or Boxster? Venting the rear engine cover/lid has big effect on cooling.

How do those two BTM aero rules apply to rear mid cars like that?

Thanks

 

 

Same rules apply. As long as you follow section 6.3 you can take the BTM Aero credit.

 5)  Hood replacement/modification for venting and/or weight reduction (“aero” hood pins are permitted).  

6)  Removal/cutting/drilling of the fascia for engine cooling, air intake, brake ducting, and transponder mounting purposes. 

Let me know if it answers your questions. 

Roman

[codename Bil Doe]

I believe so. This would mean front hood and rear engine cover modification is ok for cooling and btm aero for rear mid engine cars. Thanks for the clarification

[esr]

I see some hood vents have fins that protrude above/higher than the the surface of the hood, is this legal for ST4?

[Roman V.]

On 3/20/2019 at 7:02 AM, esr said:

I see some hood vents have fins that protrude above/higher than the the surface of the hood, is this legal for ST4?

Do you have some pictures of what you are talking about?

[esr]

On 3/20/2019 at 3:55 PM, Roman V. said:

Do you have some pictures of what you are talking about?

Sorry I don’t have pictures as I haven’t purchased it yet.

 

[Greg G.]

Hood venting is permitted, but the ST4 Aero rules are more stingent than those of ST1-3, and do not list an allowance for "Fins" or "Louvers" or "Slats" that protrude above the hood that could possible function as winglets or hood "canards".   There are plenty of aftermarket hood vents that are essentially either flush with the hood (or perhaps have a 1/4" high surround for mounting purposes), and there are other vents that have louvers or slats that are beneath the hood surface that would also be permitted.  This would also apply to BTM Aero in ST3, and all in ST5-6.

[David Sk.]

Hello I dont see in the ST5 rules where it talks about hood vent dimensions only that hood vents are allowed can you help me find it.  I was thinking about getting this but I am confused about your comments. 

https://www.ebay.com/itm/DMAX-STYLE-HOOD-VENT-UNIVERSAL/263415072505?hash=item3d54c306f9:g:uIEAAOSwrklVblAa  

[Roman V.]

1 hour ago, David Sk. said:

Hello I dont see in the ST5 rules where it talks about hood vent dimensions only that hood vents are allowed can you help me find it.  I was thinking about getting this but I am confused about your comments. 

https://www.ebay.com/itm/DMAX-STYLE-HOOD-VENT-UNIVERSAL/263415072505?hash=item3d54c306f9:g:uIEAAOSwrklVblAa

2

The hood vent can be any dimension as long as they are used for venting of the hood.

From the ST5 rules 6.1.4 

5) Hood replacement/modification for venting and/or weight reduction (“aero” hood pins are permitted).

 

From Greg:

Quote

There are plenty of aftermarket hood vents that are essentially either flush with the hood (or perhaps have a 1/4" high surround for mounting purposes), and there are other vents that have louvers or slats that are beneath the hood surface that would also be permitted.  This would also apply to BTM Aero in ST3, and all in ST5-6.

 

The vent in your link is good to go!

Let us know if you have any other questions. 

[David Sk.]

Thanks for the reply but I am even more confused.  You say the vent can be any dimension which is what I thought however Greg G. was talking about being flush, and nothing sticking up and then says the flange can be 1/4" above the surface and I was curious were this was in the rulebook so I can make sure all is good before I buy it.  BTW the vent on ebay I was looking at is about 2" tall, at least thats what they said. 

[Roman V.]

2 minutes ago, David Sk. said:

Thanks for the reply but I am even more confused.  You say the vent can be any dimension which is what I thought however Greg G. was talking about being flush, and nothing sticking up and then says the flange can be 1/4" above the surface and I was curious were this was in the rulebook so I can make sure all is good before I buy it.  BTW the vent on ebay I was looking at is about 2" tall, at least thats what they said. 

3

Looking at the vent picture again on eBay, the vent does not have any holes in it. It is for style purposes only. 

Something like in the picture below is legal. 

If you have hood vent fins sticking above the hood, they can be considered hood "canards" and thus perform an aero function which is not allowed in the rules. If the rules do not call for something specifically to be allowed then it is not.

Hope it makes sense.

 

[David Sk.]

I was going to cut out the back sides of that ebay thing so its a functional vent.  Where in the rules does it say a vent cant perform and aero function?  Dont all vents perform and aero function by letting out the air helping cooling and lowering under hood pressure which probably helps reduce front lift.  You stated the if its not in the rules you cant do it but I saw somewhere it actually said mods where unlimited unless noted?  When I get a chance I'll have to read the rules again.  Thanks.

[Roman V.]

3 minutes ago, David Sk. said:

I was going to cut out the back sides of that ebay thing so its a functional vent.  Where in the rules does it say a vent cant perform and aero function?  Dont all vents perform and aero function by letting out the air helping cooling and lowering under hood pressure which probably helps reduce front lift.  You stated the if its not in the rules you cant do it but I saw somewhere it actually said mods where unlimited unless noted?  When I get a chance I'll have to read the rules again.  Thanks.

Of course, they perform an aero function. But they are not considered a "canard' which is a different aero device. 

[Greg G.]

"If not using the BTM Aero Modification Factor, aerodynamic parts/devices/aides shall be limited in ST4 to the following:..."

ST4-6 Aero rules are limited to what is listed as permitted, which is different than ST1-3, and different than other modifications that are listed as being open if not listed as restricted.

[David Sk.]

I see btm rules allow for hood venting but I dont see any other rules regarding what kind I can or cant use.  I am not putting a canard on my hood I am putting a hood vent on.  If there is nothing that says what kind of hood vent can be used then I assume I can use the one I was looking at on ebay or any other hood vent for that matter.

[Greg G.]

This is the definition of a vent:

vent¹

/vent/

noun

noun: vent; plural noun: vents

1. 1.

   an opening that allows air, gas, or liquid to pass out of or into a confined space.

   synonyms:

   outlet, inlet, opening, aperture, vent hole, hole, gap, orifice, space, cavity, cleft, slit, pore, port;

 

The ST4-6 rules state that you can do anything that is written as being permitted in the BTM Aero rules, and then lists the other Aero modifications that are permitted.  So, if you place something on your hood that is more than "an opening that allows air to pass out of", then you are very possibly subject to protest and disqualification or Tech inspection and disqualification.  Anything that you put on the hood that is above the hood surface (such as slats, louvers, Gurney lip) may be considered a winglet or canard, or just an alteration of body lines that functions another purpose other than those listed as permitted for hood venting or weight reduction. 

I don't understand why you would now assume something opposite of the answers you have been given.  Roman showed a great example of a vent that has slats or louvers that would not pose any issue with the rules.   There are extremes that could be taken with these modifications (like putting a 4 foot wide 9-12" high front air dam/wing on the front of the hood and then claiming it was part of the vent behind it) using your interpretation.

[David Sk.]

I am simply trying to get a straight answer before I continue to poor money into this project car.  My dad always said read the rulebook as the only rules are whats written in them.  Per your definition of a vent/venting any device that has an opening and lets air pass in or out is a vent and venting.  Since I dont see any limits on venting and since a rule says unless otherwise listed mods are unlimited its open to anything at least thats how i read it.  The issue I have is you and romanV are now putting limits on them when its not in the rules.  Is it flush? not in the rules.  Is it less than 1/4"? not in the rules.  Now if the rules said all vents must be this size by this by this size we would be happily wrenching away instead of trying to sort this out.  Is it possible to request a change so its more clear?  How would that work?  Thanks.

[Greg G.]

David,

If the rules didn't state this, you would be 100% correct (which is why one can have a hood vent in ST1-3 with 1 foot high "louvers" that also function as hood mounted air dams).  Aero in ST4 is a special case in the ST1-4 rules:

"6.4.2 ST4 Aerodynamic Modification Restrictions and Limitations
If not using the BTM Aero Modification Factor, aerodynamic parts/devices/aides shall be limited in ST4 to the following:"

We (National Officials) spoke about this recently, and decided that there was enough there to prevent someone from going beyond what is listed ("Hood replacement/modification for venting and/or weight reduction") and using the rule to perform functions that are not listed and/or specifically prohibited.  When we start writing rules that give exact specifications for parts that can vary so much, yet perform the same function and no other function, we just pigeonhole ourselves and the competitors into possibly having to DQ someone for something ridiculous.  Let's say the rule specified a maximum of 1/4" high mounting lip for a vent insert into a hood.  Then, someone shows up with a 3/8" high lip around the entire hood vent insert---DQ under a protest, but silly.  Or, worse yet, the hood vent gets loose sometime during the race, and when the car goes to tech, it is now 3/8" off the hood surface.  No Official wants to DQ someone for something like this---Well, in reality, regardless of some opinions out there, 99.9% of Officials (including me) never want to DQ anyone for anything, but are forced to based on non-compliance. 

I suppose we could have a chat about a rule clarification that the "only" function can be for venting, but the rule already says for venting or weight reduction, so adding the word "only" seems to be unnecessary.  But, would that word ("only") have made you stop and not put 2" high louvers above the hood as part of your vent?

 

[Greyout81]

David,

in my OPINION that vent could only be run if it was mounted from beneith the hood. (But keep reading, I disagree with myself!)

the lateral dimensions are not the issue...  adding something (big or small) that sticks up above the hood is the issue.

I’ve attached a picture of a hood vent in my wifes miata.  They are mounted from below, but would still not be legal because the fins stick up above the hood slightly.

The only grey area that I think could be explained better in the rules is permitting a cosmetic trim piece around the cut edge to smooth out the cut metal.  I have what is essentially flexible door trim around the cut hole, and technically thats not legal, though I think that should be.

Greg:  a 1/8” or 1/4” dimension could be given, but drivers would need to toe that line just like any other line drawn in the rules - it would be foolish to run your car within 1hp or 1lb of your classes limit for example

Your pictured vent is fine but to be safe, I would mount it from below the hood.

 

 

Edited March 27, 2019 by Greyout81

[Greyout81]

Well, aftering going back and reading the rules again (that always helps):

“Front wing/spoiler/foil/splitter may not protrude more than 12 inches in front of the outermost edge of the front bodywork/fascia, and may not be higher than the lowest part of the vehicle’s hood”

 

so a couple things:

-the rule addressing things sticking above the hood apply to “front wings, spoilers, foils, and splitters”.

And

Not “sticking up above the hood”, but “can’t be be higher than the lowest point of the hood”

Soooo that means, assuming your car is like most cars and the lowest point of the hood is down in the front, you can’t have a “foil” UNDER the hood further back, if its still above the lowest point?

I guess then you have to work to define a foil vs a duct?

Dictionary, if you look up airfoil: 

1. a structure with curved surfaces designed to give the most favorable ratio of lift to drag in flight, used as the basic form of the wings, fins, and horizontal stabilizer of most aircraft.

By defintion a gurney flap is not an airfoil.

it seems the intention of the rule is to address wings and splitters on the outside of the car up at the front, but ANYTHING on (or even under!) the hood meant to direct air could get tripped up by this.

Edit:  it really hinges on what portion of the car “Front wing/spoiler/foil/splitter” rules apply to.  You might have a gurney flap in the middle of your hood, and be able to say “well thats not the Front wing/spoiler/foil/splitter”

Edit edit: after all this, my interpretation of the rules as written is that the vents installed as shown in the picture is legal

 

Edited March 27, 2019 by Greyout81

[David Sk.]

Well the way I reads the rules is 1. unless otherwise noted mods are unrestricted.(per the rulebook)  2.  btm then restricts the body/aero to factory specs with the following mods.  3. then says venting the hood is allowed mod.  so if it is an allowed mod then it no longer falls under btm aero and so venting the hood goes back to being unrestricted in the 1st rule.  I would have no problem conforming to a written rule if it said a vent must be this size by that size or green or blue.  The issue is they dont want to put a spec on it which leaves the racer hanging in the wind on what a go or no go.  They spec tire width, hp limit, weight min, wing sizes etc but cant simply say it can only be 1" tall.  Then everyone would no the rules, everyone would build to the rules and we wouldnt be having this issue.  uhg.

[Greyout81]

While the venting of the hood is an unrestricted mod, you must do so within the scope of the other rules.

the rule preventing mods “above the hood” actually says “above the lowest point of the hood”.  The reference line that prohibits aero devices is actually well below your vent.

So, you are free to vent the hood as long as the bits that go with that serve only that purpose and can’t be labeled a “Front Wing / Spoiler / Foil / Splitter”

The word “foil” does not appear in the dictionary in any aerodynamic context, so the conclusion then is to use the word airfoil.

Read the definition of: Wing, Spoiler, Airfoil, and splitter.  Splitter may need to be identified using a definition from the rule book rather than a dictionary.

A gurney flap is not a wing, or an airfoil, or a splitter.... might be a spoiler??

However the ducts you posted a picture of are definitely none of those things.  There is no example of a wing / spoiler / foil / splitter you can find that utilizes an upsidedown wedge shape.

at the end of the day it will come down to the race steward at your event but I feel like this is a solid arguement.  

This happens to pro race teams too - a part is designed to fit the rules, FIA decide the part serves as <insert banned part here>, and shit now we gotta change it.

I think you’re good though.

edit:  I see where I might be missing the point - its not running afoul of the added aero rules, its the BTM points allowance.

gonna read some more...

 

 

 

 

Edited March 27, 2019 by Greyout81

[Greyout81]

Ok!  I still think you’re good.

what it does NOT say:

You can cut a hole to vent the hood.

 

what it DOES say:

You can MODIFY THE HOOD FOR VENTING

cut & dry.  Do whatever you want to the hood as long as it serves the purpose of venting and nothing else.  The rules do not tell you the only way to vent the hood is cut a hole and hope the air flows the right direction 

Edited March 27, 2019 by Greyout81

[Dan Howard]

Can anyone show me a photo of a "hood canard"?

[Greyout81]

Never seen one!  But I’ve see an APR Wing on a hood lol