Tofuman FC3S

iTrader: (1)

Hey Ramy,

Like Mike said above, you are asking wether air will enter at the windshield (making it inlet, not a vent). Normaly the awnser is yes. Also like Mike said this would decrease the effectiveness of the radiator, since the pressure will built up in the enginebay.

What I meant in my post (maybe you should read it again) is that a vent (not inlet) would work, aslong as the airpressure in the enginebay is higher than at the base of the windshield, it would vent. I don't know however how high the pressure at lets say 100 MPH is at the front of the windshield, actualy I have no idea! Let's asume just for the fun of it that it's 50% higher than ambient at 100 MPH. Now in this scenario the front went is airsealed to the intercooler, and so will only vent air passing thru the IC. The rest coming thru your radiator and other big-*** holes of your bodykit will go in the enginebay and make the pressure rise there. Let's go crazy and say that it will built up to 80% above ambient at 100 MPH in the bay. That 30% more pressure in the bay would make the "windshieldbase vent" effective for that much.

But without measuring and testing I wouldn't assume this. At one point (meaning at a certain speed (might be a 100 or a 1000 MPH)) the windshield vent should work, simply because of the pressure difference. As I'm writing this I'm already wondering howmuch pressure at windschield base would increase as car speeds increase... Huh... This is going nowhere, and lets just ASUME they are ineffective! It would kick *** though if someone where to test around a bit. Anyone know if small airpressuresensors are commercialy available?

You PM'd me? I didn't get one? About what? Does this forum require minimum amount of posts before recieving PM's?

Riz.

FDNewbie

iTrader: (10)

It seems I've thoroughly confused the both of you haha...but the important part is, that together, you've both covered the points I was trying to raise!

http://www.dmax-cs.com/bonnet/b.gif

Yes.

Now your asking if the air entering the rear of the hood help keep underhood temps down because of this?[/quote]Negative. I was wondering if SINCE the front duct was "ducted off" and no engine bay air would be exiting from there (except what passes through the IC, which would be ducted anyway), then could I end up having a hood that worked as shown in the diagram below, where the front vent vents only the IC, and the rear vent ACTUALLY vents the engine bay compartment?



But, as Riz has already clarified, it's probably not doable, and even if it is, not very well. You both also brought up the good point about since air is more likely to ENTER through the rear ducts (when I was hoping it would EXIT through there), that I'd be (re)pressurizing the engine bay, which would result in increased backpressure behind the radiator.

So, forgive me for making this complex, but here's the two scenarios I'm curious about.

1) If I seal off the undertray, so the radiator truly has no where to vent except through the rest of the engine bay compartment, would THAT result in making the rear vents functional? Prob doesn't sound like a good idea (lol) but I'm curious nonetheless. I'd *guess* that even if it was functional, the oh-so-indirect route the air would be forced to take would leave enough backpressure behind the radiator that it would be inefficient at best.

2) So, according to my original plan, the IC is vented to the forward vents. The radiator has its own vents to follow through the (custom) undertray, exiting out under the car (wouldn't that promote lift, however?).

- So now, what can I do if the hood already has the rear vents?

- Would it help if I tried this... See how the front vent is actually composed of several vents (four I believe)....what if the IC was vented to say the last 3, and the first one was left to vent the engine bay? Or visa versa (the first 3, w/ the last for the engine compartment).

Basically what I'm after is, what's the best way to provide excellent venting for both the IC and the radiator, without compromising overall aerodynamics (pressure buildup in the engine bay = pressure buildup at the nose/airdam of the car, which isn't good, so I'd think SOME engine bay venting would be good), and I'm still unsure if venting the radiator back under the car is such a good idea when front end lift is a major concern of mine. That's why I was initially hoping venting through the rear hood vents (outward) would be a good idea.

Makes sense.

LOL sorry. I PMed Mike. But you answered my question about functionality of the rear vents

TIA,
~Ramy

Tofuman FC3S

iTrader: (1)

LoL, yeah quite confusing! Doesn't help that English isn't even my second best language either! HaHa!

It is a good idea, but only if you were to creat groundeffects, and make a flat underbody. You would then need to find ways to vent the air out the enginebay... Probably through vents in the frontfenders, or maybe below the doors (completly redisign you car!) like the DTM cars have. The one infront of the windshield would still not be the best choice, but the pressure has to go somewhere, right?

That way the enginebay SHOULD be entirely airsealed, and the only air that would come in or go out would come through cranks between bodywork. Venting below the car would change airflow (probably for the bad), and wouldn't be nice if you designed/calculated you flat underbody prior to this, not counting in the air passing through radiator.

Test for your specific aplication and decide, or guess the fuctionality and decide. If you choose to guess I'd advice on guessing that it don't work, and seal them.

That would in my oppinion be more effective then any vent no mather how big at the base of the windscreen. It's just the perfect place to vent. You would loose in theory 25% effectiveness of IC venting though.

The only reason I got into this convo with you is because I can see that you care alot about aerodynamics, and have the same mentality as I have: Function over form. For pretty much every other member I'd just advice to get what looks best to them, since that's their main priority.

Well, that's a first in this topic! LoL!

Yay!

I like the way you think, and I hope I'll soon have a FC to modify it with the same views on upgrading you have when you mod your FD.

Good luck,

Riz.

FDNewbie

iTrader: (10)

Haha my bad man. I'm gonna take a stab in the dark here, but is your first/second language Urdu by any chance (assuming Riz is short for Rizwan)?

Already doing that. Gonna have a front lip that extends just a bit forward from the front bumper lip, and continues ALL the way back, past the oil pan. Hoping venting the air that far back will not only reduce turbulence & lift, but also provide some additional oil cooling, since the air will have to pass right past the oil pan

Dude...you're THE MAN. You just reminded me of something I had completely forgot about. One of the 3rd Gen guys actually removed his fender linings and replaced them w/ a mesh...and measured a *noticeable* difference in acceleration...which we attributed to considerable decrease in engine bay (and thus front nose) backpressure: https://www.rx7club.com/3rd-generation-specific-1993-2002-16/want-cooler-engine-bay-without-changing-hood-530715/. Here's a pic:



I'd like to avoid the other vents (eg the fender vent) because I'll be making custom ducts and dedicated "runners" for the oil coolers & brake vents.

Understood.

I think IF the angle isn't too sharp, even WITHOUT ducting (although I would duct it anyway), sealing the bottom off 100% and vending the V-mount radiator out to the fender lining (which would now be a vent) with a splitter in the middle (to direct to the right or left fender vents) would be PERFECT!!

Or not waste time w/ such a hood in the first place.

That's the issue...I'm sure that multiple vents such as in that hood are much more efficient at just that: venting....than say, a single vent such as the one in the hood I currently have (see picture below). In fact, I can tell you first-hand that the hood likes to lift up pretty well when driving at high speeds, telling me there's a considerable amount of pressure built up in the engine bay that isn't being relieved as well as it should be from that small - and singular - vent, vs. the multiple in that D-max hood, which are very well placed, might I add. Filling in the rear vents would simply suck...and look crappy I'd think.



It's much appreciated

Absolutely!

Thanks! I'll be sure to post up when it's all said and done... and you do the same!

~Ramy

One more question... So if the pressure is high in the rear, and venting is prob. not doable there, why did RE-Amemiya choose to place two vents in the rear of their hood, which is one of only two FD hoods (the other being the Mazdaspeed R-Spec hood) that have ever actually been R&Ded w/ wind tunnel testing? They using it for something else?

NZConvertible

I know you're just making numbers up for the sake of discussion, but I don't think many people appreciate the magnitude of the pressures we're discussing here.

The static pressures measured across the top of the hood would be in the order of a few hundred pascal's, compared to atmospheric pressure of 101,325Pa at sea level. So a measured static pressure of 250Pa (which is realistic) is only ~0.25% of atmospheric pressure. Dynamic pressure at 100mph is ~1200Pa, which is a lot higher than the static pressure but still only a small fraction of atmospheric pressure (~1.2%).

I just think that needs to be kept in perspective.

FDNewbie

iTrader: (10)

So for the less physics-inclined that 1200Pa is the pressure pushing air INTO the rear vents, right? So you'd have to overcome ~1200Pa before you had ANY flow exiting the rear vents, correct? And any idea what kind of engine bay pressure you'd be building up at 100mph? Just out of curiosity, as I think we're in agreeance that rear vents are not the way to go.

Tofuman FC3S

iTrader: (1)

Nope, 1st is Dutch, 2nd German (languages of my parents) and 3rd would be English then. Riz is just some letters of my first and last name combined.

Sweet!

That's what the ladies say atleast... Sorry had to make that comment!

I can deffo see air leaving there, also water entering though...

I'd say go for it! Howabout instead of mesh, you use fins? That would keep the above mentioned water out of the enginebay. With mesh it will spray up, and it depends on what you got close in there that doesn't like water.

Hood looks nice. look at these facts: 80% of hood surface is low pressure (pulling the hood/car up), The shape of the vent will increase this effect, you hood is made of LW materials, and there is some pressure under the hood. Those combined WILL make your hood wanna pull up. Atleast if it's pulling/pushing more up than gravity pulling it down, and when you hit a small bump it will want to do so even more.

Will take alot of time to wait for mine! If I lived in the US I would probably be driving a FC right now, but being a Dutch full-time student living on his own is making stuff alot harder to do.

I dunno how the development went. Maybe they created the hood first, and checked it later, or thought it looked nice... Maybe they work because they are on the sides of the main vent and influenced by them. They are alot closer to the front then the FC hood in this discusion though, the rear vents on that one are realy on the edge of windshield. Maybe they are on the edge of posiive/negative pressure, and air just flows out because the enginebay is pressurised? I truely don't know. RE-A Porsche headlights don't do anything for aerodynamics either. I would maybe mail them and ask them?

HaHa! Wow! I was a bit off I guess... LMAO! Yeah, realy don't know the figures, never studied anything of this. I do however feel like I get simple aerodynamics (like the first aero car designers, who just designed what looked areodynamic), and got a feel of how air will flow. I'm glad you put some figures in the talk, so I can understand with what range we are working. In my defence: it's 4 in the morning here, so I might be saying: "Ah what the hell, lets just take 50%" easier then I would normaly! hehe... But does the rest of our talk make some sense?

Riz.

NZConvertible

No, dynamic pressure is the pressure acting in the direction of the car's travel, i.e. what you feel when you stick your hand out the window. The only parts of the car that'd see that sort of pressure are those that directly face the airflow. The static pressure differences are mainly what causes air to flow through bonnet vents and any other holes perpendicular to the airflow.

Way too many variables to guess, but it would be in the order of a few hundred pascals probably (or a few hundredths of a psi).

Absolutely.

FDNewbie

iTrader: (10)

The original poster was asked about that, and h said his engine bay was no more cleaner or dirtier than before, leading me to think that as long as you're at a relatively decent speed, the airflow through them to the outside was sufficient to keep other objects from coming in. But of course, going slow through rain & puddles may be quite different.

I think the fin idea is prob a better idea; something w/ many fins much like the hood. Best of both worlds

I feel you, but you'd agree that the D-Max hood w/ multiple vents (4+) would do a much better job at venting than my single-vent hood, right?

I feel you, but don't think mine's on it's way to completion either. I'd say I'm about a year out EASY.

Gotcha And thanks for the clarification!

~Ramy

drftwerks

iTrader: (1)

hahah who gives a ****, its a ******* fc, for the street.

FDNewbie

iTrader: (10)

A) Not everyone only has an FC

B) Not everyone uses their rotary as a street car; some of us are building dedicated track cars.

drftwerks

iTrader: (1)

honestly what will the time diff be between these aftermarket hoods, since this thread is about hoods

and to take full adv of the aerodynamics, wouldnt the whole body of the car have to contribute??

FDNewbie

iTrader: (10)

Time difference? I have no idea what you're asking.

As for the hood, MY posts were in reference to performance & cooling, not downforce, because a hood in it of itself cannot generate downforce; that would be the function of a collection of aerodynamic aids on the vehicle, which the hood is a part & parcel of.

Tofuman FC3S

iTrader: (1)

Hmmm... OK.

Yeah, that would be the cleanest.

100%! Especialy when ducted to VMIC.

Yeah, life's a bitch and then you die...

We are discussing using the info gathered in this topic on his FD. Not everyone drives their car strictly on the street, and certainly not as a DD. We obviusly GIVE A ****, or we wouldn't have this talk. I just realy don't see the point in buying a hood that doesn't do anything but look pretty and fast... Maybe I'm not a big enoughh of a ricer. The whole point of upgarding cars is taking what was designed and improving it, manufacturers of affordable cars always make concession for sale abbility, legal stuff, stafety, comfort or other stuff that might not be such high priority for us as the average driver.

Yeah, it's about cooling. Hoever increasing flow trough the intercooler substancialy would lower intake temps, increasing power. Also the air passing though the car, instaed of being pushed infront of it would help at speed. When you duct the air bhind the radiator away (creating lower pressure bhind it), you would need a smaller gap for the radiator to achieve the same cooling performance. This means the V-Mount splitter could split more air through IC meaning better power. Whether the whole body would have to contribute? Sure in the ideal situation it would. We are just brainstorming now, but if you could redesign all bodypanels with help of computer calculations and a windtunnel it would be awesome, I guess it just depends on how much you wanna invest and care...

Riz.