FDNewbie

iTrader: (10)

Can anyone shed some light on the purpose of the side vents on some aftermarket front bumpers, near where the bumper & fender meet? These vents appear to be venting air OUT of the side airdams (which typically are used to direct airflow to and through the oil coolers). I'd think you'd want to KEEP focusing that that air toward & through the oil coolers, not venting air away from them (essentially robbing the oil coolers of air). The only explanation I can come up w/ (my guess) is that it helps decrease air resistance through the front nose Any comments/explanations?

Here are a few examples of the side vents I'm talking about...and I'm sure I can find a few more if I had free time on my hands As you can see, some of these vents are pretty substantial in size...

PanSpeed:




C-West:




Knightsports:




Mazdaspeed:




Thanks,
~Ramy

bajaman

One would assume that unless some dedicated airflow research has been done by the companies offering those kits (unlikely) that indicated a 'positive pressure' area that required venting, the vents are simply cosmetic. I am sure they somehow add 30 hp....

TRISPEEDFD3S

iTrader: (26)

Wrong bajaman, they add 35 HP...

FDNewbie

iTrader: (10)

Yes, I'm with you...only problem is, Mazdaspeed DOES indeed wind tunnel test it's body parts.

And to add to the equation, it's long been held & proven that vents in the rear of the hood (near the windshield) will actually result in air INFLUX, not outflow, yet RE-Amemiya (which is the other company that wind tunnel tests it's products) has rear vents in it's hood...



So my question is simple. Does anyone know the rhyme or reason behind such vents? If yes, great. If not, thanks for your time...

FDNewbie

iTrader: (10)

Oh and I'll add that not only do some of these companies actually wind tunnel test, but some of them hold track records for the fastest lap times around various tracks (PanSpeed, R-Magic, etc) - and such accomplishments don't happen via haphazard aero parts + a ton of fancy stickers. So lets not be so fast to speak ill of those who are *clearly* doing much better and more than we ourselves are

KaiFD3S

iTrader: (37)

I'm no engineer, but what I thought it did was to directly vent out the air from the oil cooler hence making the oil coolers more efficient, instead of the air having to pass through the whole wheel lining and out the side fender vents.

TRISPEEDFD3S

iTrader: (26)

Rmagic also has downfornce fenders! Also, about the hood ramy...was the air influx from those folks using spacers on the hood hinges to raise the rear of the hood? If so, maybe the air influx doesn't happen with the re hood because the rear is sealed by that back hood seal...Just throwing out ideas here...

TRISPEEDFD3S

iTrader: (26)

Makes sense Jan...so basically taking out hot lingering air that is trapped, since the back of the oil cooler can only let so much air flow out!

mono4lamar

iTrader: (32)

I'm with Kai. With the "vents" there they actually allow an escape for the air. With that I believe they allow the oil coolers to BE more efficiently. No reason for a long explanation my answer is short...

FDNewbie

iTrader: (10)

Ah! I'm such a dork! The oil coolers are BEFORE those vents, aren't they? So the vents are BEHIND the coolers, to reduce backpressure and thus help increase flow THROUGH the cooler! haha. My bad

Huh?

I know what you're saying, the cowl effect, which died out in the late 90's/early 2000 in Japan. But even with the weatherstripping in place and the rear of the hood in the same position/angle as stock, aerodynamically speaking, the base of the windshield is a *major* positive pressure area. This is obviously for an FC, but the principle still applies (I have yet to find the same diagram for the FD by Mazda). The huge pressure area there is exactly *why* a cowl hood works.



~Ramy

KaiFD3S

iTrader: (37)

So what do I win Ramy

FDNewbie

iTrader: (10)

The right to shut the...

LOL I'm just playin I shouldn't ask questions when my brain's tired...

B_Hydra

iTrader: (1)

Sorry to veer the thread off topic , but which hood is that on the yellow FD (first picture)?

Thanks!

RXtacy

iTrader: (7)

As you see in the flow profile the positive pressure area shown on the FC is right where the hood meets the windshield. I would imagine the FD flow diagram would be similar if not slightly improved in regards to the area of positive pressure. Thus I would imagine that the RE-Amemiya hood with the rear vents is in front of the positive pressure area.

wReX

iTrader: (6)

some cool pics

FDNewbie

iTrader: (10)

It's on the PanSpeed car so naturally, it's the PanSpeed hood (which I can get for you if you're interested)

Zup engineering boy I disagree. Take a look at how far back those vents are. They're pretty much in line w/ the windshield fluid nozzles. That's pretty darn far back. And even if we entertain your idea, and say it's slightly behind the area of greatest positive pressure, if you take a look at the flow diagram again, you'll see the positive pressure is concentrated at the junction of the hood & windshield, but is *distributed* throughout a wider area, which includes the lower part of the windshield and the rear part of the hood. So at BEST, I'd say you're looking at a zero to less positive pressure area. Still pretty darn poor placement for vents IMO...

...UNLESS that flow diagram (which is 2-D obviously) does not show us that the high pressure zone drops off as we move laterally...which would create a nice low-pressure zone for those very laterally placed vents to work in. MAYBE lol. I'll have to consult my Yamaguchi on that one...(when I get some free time).

~Ramy

RXtacy

iTrader: (7)

The area over which the pressure is distributed is minimal. Also that is not an extremely technical model so it is impossible to tell exactly where the pressure difference occurs. I also would believe that the area would be smaller on the FD due to greater aero dynamic efficiency. However this is all speculation I have not wind tested an FD ... unfortunately. I do feel that if RE-Amemiya does aerodynamical testing, then those vents would have a positive effect.

Kento

Basing everything off an aerodynamic pressure diagram that's not guaranteed to scale (nevermind for an FC) is quite a stretch. There's a ton of variables that will determine how far back the positive pressure "backflow" from the windshield/hood junction will spread, not the least of which is the exact angle, surface area, and relationship of both the hood and the windshield. Just for starters, not only could the windshield on the FD (both stock and RE-Amemiya) be canted slightly farther back (less), but the chassis angle of the car itself will affect it as well, since that will change the angle of the windshield. Then you've got the fact that the turbulence created by the hood vents will change the pressure at the windshield/hood junction as well, since that will affect the flow speed. There's more factors as well. I'm not saying that the RE rear hood vents are truly functional, but don't conclude that one very generalized diagram applies to all cars, nevermind between the FC and FD.

MrNizzles

iTrader: (5)

bitchin photos, saved those for sure!!!

I wish that the 3rd photo, with the silver FD had little flags placed all along the opening of the front vent on that hood... I wonder if they would be flowing in an upwards direction, possibly indicating that the hot air underneath the hood is being venter upwards or out of the engine bay. I also wonder what the air temp in the front of the engine bay is with that vented hood and with the stock hood. Would be some nice numbers to have.

TRISPEEDFD3S

iTrader: (26)

I was just talking about the wide fenders the make. Supposively they're supposed to increase downforce or something...Go R MAGIC!

primerGrey

iTrader: (13)

I agree. Another important factor is the placement of the RE-Amemiya rear vents far to the sides. The positive pressure zone will of course extend furthest forward on the hood at its centerline, and the least forward at the sides (something the side-view FC diagram won't show). From the angling of vents, perhaps they were placed as far back as possible without extending into the positive pressure zone.

As usual though, its all speculation without any test data.... Test data that is easy to get however. If anyone has this hood, attach some string or teflon tape to the lip, drive the car down the road, and tell us if the string flys into or out of the hole.

FDNewbie

iTrader: (10)

Not to doubt you Kento, but what would lead you to doubt that it's drawn to scale?

And yes, it's a different car w/ a diff chassis, but I'm fairly certain that the high pressure zone between the rear of the hood and windshield holds true for virtually ALL vehicles w/ similar/comparable construction.

Agreed. I took a look at the comparison they had in Yamaguchi (of body contour), and while the FD was a bit more swept back & aerodynamic, the overall angles & shapes were very similar. Again, I'm not saying the aerodynamics will be identical, but I believe the two cars are close enough that data gathered from one can be used to give you a pretty good (although general) idea of what it *should* look like on the other.

I understand. Again, just making a general comparison. You would agree w/ me that it's pretty apparent that there will be SOME positive pressure in that juncture, correct? How much may vary, but we know that's a constant. And that's what I was getting at...it's a high pressure area for sure, so why vent there?

Again, I understand and agree, but I was merely using an example to make a very (in my mind) sound generalization that that area WILL be of high pressure. How far back, how wide, etc, that's beyond what we can assume. But I don't expect the entire area to suddenly change from a high to low pressure zone...

Yes, I didn't have any trouble understanding your English my friend What I meant was, where'd you hear/read about the fenders increasing downforce? That's a first to me...

I'm guessing you're talking about their new-ish fenders w/ that sharp angle going along the top 1/3... I may be way off, but I'm suspecting that works much like the RE-Amemiya & FEED fenders (that completely eliminate the oil cooler vent in the fender) and leave open room for the air behind the wheel to vent. I'd imagine that has something to do with turbulence and/or lift, so in that sense, maybe it does decrease lift. Have NO idea how though. But I can tell you this...the design was used on the FC3S IMSA car, and apparently adopted by RE-Amemiya on their JGTC FD, then picked up by a few other Japanese tuners...

FC3S IMSA Car:




R-Magic Fenders:




RE-Amemiya Fenders:




FEED Fenders:




Which naturally takes me to my next question...

Note that most of these cars do NOT have oil cooler duct vents on the side of the front bumper. AND the fenders eliminate the OEM oil cooler duct vents. So...how/where are they venting the oil cooler ducts to? scratch:

~Ramy

DaveW

As one of the posters above alluded to: The pressure profile Ramy posted is at the car's center-line. As you get nearer the edge, the air has an escape route around the sides of the windshield (and this path around the windshield is curved, also lowering the pressure - similar to the convex top of a wing), and pressure will be much lower, maybe even below atmospheric. So, hood vents near the outer, rear corners of the hood may effectively evacuate air from under the hood.

Kento

What would lead you to believe that it is? Just because it was published from a Mazda-related source? Unless you've got graphics that demonstrate that it is (and even that is no guarantee), you can't base very much off of it.
Where did I ever state that a high pressure zone at that point didn't hold true for all vehicles with differing angles of hood line/windshield? Read my post again. I'm stating that the zone varies enough between all vehicles (especially a highly modified and stock one) that assumptions such as "it's a positive pressure area there, and this rough diagram of a different car shows the backflow spreads to the general area of the vents on a highly modified car, so the vents on that highly modified car must be in a positive pressure area" are a complete stretch. Your general comparison used to conclude that the vents on the RE Amemiya car are in a "high pressure area for sure" is akin to saying that just because two jet aircraft are close enough in "overall angles and shapes" that their aerodynamics should be similar enough. You don't know the chassis angle, nor the hood shape, nor windshield angle, nor the effect of the hood vents, et al, of the RE car, so you cannot make a "sound generalization that that area WILL be of high pressure."
Agreed, and definitely an important factor I didn't mention.
They usually vent to the wheel wells, because the airflow passing over creates negative pressure that pulls air from that area (it's why brake dust settles on the outside of your rims). Note that the bodywork on two of the cars is concave just behind the wheel/tire, which helps accentuate the negative pressure zone in that area.

FDNewbie

iTrader: (10)

Cuz I'm a sucker and I'd hope official diagrams would carry some accuracy w/ their authenticity lol. But you may very well be (and prob. are) right, in that it's a general "overview" and not to scale whatsoever.

You didn't state that explicitly, but it seemed like you were saying I couldn't ascribe ANYTHING to the FD from that FC illustration. Maybe that was misunderstanding on my part. I was simply making the point that I think all cars w/ such an interface will have a positive pressure zone there to some extent.

I agree. And not only do I agree, but I also already entertained the "important factor" that you didn't mention in my earlier post The first paragraph was simply stating that it looked (to me) that the vents were not far back enough to assume they were past the positive pressure area, cuz they're pretty far back. And the second paragraph was me pointing out that I think it has to do with them being placed so laterally, because based on my poor-man's extrapolation (lol) they didn't look far enough back.

And before you say it, yes, you're right, that's a lot of assumptions. BUT:

1) To assume they ARE far back enough is an assumption in it of itself, and
2) If you and I agree that all cars have that high pressure zone, locating a vent very near there simply doesn't sound like a good idea (which was my original point). You'd be catching either a high pressure area, equalized pressure area, or the very beginning of a low pressure area (def. not as good as say, the much more forwardly located side vents on the Mazdaspeed R-Spec hood).

And it seems we're agreeing that it's very possible that the curve of the windshield & hood may displace the positive pressure zone forward at the lateral edges of the hood, so as to leave the vents in a favorable negative pressure area.

I considered that, but wasn't sure.

Re: the negative pressure, assuming the oil ducts are vented openly to the wheel well, and you have a normally shaped fender (not concave); would there be sufficient enough negative pressure generated to vent the air in the wheel well out of the fender vent (that's normally used for the oil cooler vent)? Assuming you enlarged the vent too... Or would that be not such a good idea, and going w/ the concave fenders is the way to go? Not sure if the former would involve too much turbulence/inadequate vent size, etc.

Here are 2 examples of what I'm talking about... both from RE-Amemiya as well:





TIA,
~Ramy