Just as the thread title asks. Which way does the air flow through the stock decklid vents when the car is moving? I've heard a lot of data but don't have a car to test with, as mine is in a few different pieces around my garage at the moment. I'm looking for info about whether the air comes from under, through the engine compartment, up and out for cooling or if air cycles up from back->front and down through the vents. I've heard both but saw no data supporting either.
Reason I ask is because, while convection is plenty for a stock engine, I'm going with a non-stock, potentially turbo build. While coolant temps are not particularly beholden to under-lid temps (the radiator and cooling system does that work), the ambient temperature and heat-soak can become a problem. My 2011 Sonata Turbo was front-engine, had a huge grill to take in air, and if you drove spiritedly, heat-soak was still a major issue that destroyed performance over time 'til you let it sit and cool off. I'd rather alleviate said heat-soak as much as possible with this car. So I'm debating functional open side rockers ducted partially to wheels for brake cooling and partially to under the decklid to further improve cool air flow there, with small, low-profile fans in the deck lid vents and a third, reverse-facing functional "scoop" with a fan blowing up and out through that. Get a thermostatic switch that's mounted by the center of the firewall that controls those three fans on their own circuit. Allow them to run, car on or off, but if the car is off, don't let them run more than a minute or two because battery rundown protection.
I don't know how you could get more air in the back, there is a hole clear to the ground that you can throw a Cat through. Larry
Cats can fit through some tiny holes. Mine was an escape artist. She sadly died of old age when I was in high school, but point remains. It isn't so much as increasing volume as it is improving flow and the 'quality' of the air. There's plenty of volume, but it doesn't move much. I've noticed that, even with the stock iron duke, under-lid temps still stayed in the 55 to 65 degree Celsius range. That isn't scorching-hot but it is warm enough to be problematic for some accessories. My friend's '88 GT was a bit warmer with the 2.8. My hope is to drop that by 8-10 degrees C. That might be a bit too optimistic, but every little bit helps.
Originally posted by Ravant: but every little bit helps.
Every little bit may not help if you are at all concerned about emissions and mileage. The engines were designed to run at 85 to 110*C, so it's no surprise to see 65*C under the lid. The quality of your components may be more of an issue than the ambient temperature. Everything should be very happy at that temp, except maybe your skin.
Every little bit may not help if you are at all concerned about emissions and mileage. The engines were designed to run at 85 to 110*C, so it's no surprise to see 65*C under the lid. The quality of your components may be more of an issue than the ambient temperature. Everything should be very happy at that temp, except maybe your skin.
85-110 coolant temp. That's different than ambient temperatures. The thermostat and radiator control your operating temperature. Catalytic converters do operate better, warmer, to a point. But that's internal, not ambient temperature and is typically controlled by your EGT. Is also why most high quality cats are wrapped in heat shielding from the factory: keep the heat in and disallow ambient temperature bleed.
High ambient temperatures and heat soak are a performance killer, especially for forced induction applications. Coolant temps between 71 and 104 C depending on motor, are fine. (71 for a typical 60*v6, 104 for an average Northstar V8) But though my Eldorado ETC maintained 104 coolant all day, the ambient temps were typically kept between 32 and 54. And despite having a 303 horse V8 in a 3800+ pound vehicle, I averaged 27-31 mpg depending on how much highway cruise it saw.
[This message has been edited by Ravant (edited 04-10-2014).]
The easiest and best way to reduce under hood temps is to control heat loss from the exhaust system. Polished aluminum heat shields, ceramic coatings, exhaust wrap are all viable alternatives.
Rad fan that switches on earlier can help too. Or even a lower temp stat.
Going to be using a 185 or 190 stat. Don't want to drop operating temps. Just the ambient temps. If the turbo turns out to raise temps a bit much, I'll modify the cooling system accordingly.
More horsepower produces more heat, increasing load on coolant system. Cooling system also includes the oiling system, so an oil cooler is a good addition. The largest cause of heat in the engine bay is the exhaust system. Moving more air helps, but keeping the heat in the exhaust system has other benefits to performance as well as keeping under hood temps lower. Ceramic coating, wrap, highly reflective heat shields will work wonders. Minimize the source of your heat.
I had the stock vents, although just a different looking grill, in my Ferrari kit. It had a turbo 3.1, 4 spd in it. I used a 160* thermostat and Rodneys 175* fan switch. Never had a problem ever on cross country road trips or traffic. Some people claim cooler underhood temps by putting a backwards scoop on the decklid with an electric fan blowing out of it.
BUT the Fi-Air-O scoops were designed for the 84's with vent in the decklid (side panels are solid). They can be made very functional and get lots of air into the engine bay. https://www.fiero.nl/forum/Forum1/HTML/093730.html
The center "Indy" scoop is the one that is totally cosmetic.
Agreed. Also... wasn't the Indy scoop feeding the engine intake?
quote
Originally posted by fierosound:
Here we go again! Fiero is a "bottom breather".
BUT the Fi-Air-O scoops were designed for the 84's with vent in the decklid (side panels are solid). They can be made very functional and get lots of air into the engine bay. https://www.fiero.nl/forum/Forum1/HTML/093730.html
The center "Indy" scoop is the one that is totally cosmetic.
Agreed. Also... wasn't the Indy scoop feeding the engine intake?
On the original true SD4 pasce car, yes. On the replicas, no, it was only cosmetic.
While the scoops that replace the vents might result in air going into the engine bay, it is counter-productive. The car is designed to have air come up out of those vents, not go down into the engine bay. Having the scoops is mostly cosmetic here as well, because what you get functionally, is a small increase in drag (as you're fighting the designed air flow of the car), and a slight reduction in MPG to go with it. They do not do anything at all to actually provide any improvement to performance. If you want to get any actual performance increase with them, you're going to have to do some significant modification to your car, to get the normal airflow up and out of the engine bay, as well as the increased air volume you're now forcing down into the bay.
What dobey explained is why I asked in the first place. That is precisely why I intend to duct air from scooped quarter panels to three places each. Driver's side will cup ambient air to engine intake, brake duct and low in the engine bay. Passenger side will duct to a heat exchanger for an air:water intercooler, passenger brake and low in the engine bay. Up top, I'm going to leave the side vents to convect naturally, but also add a rearward-facing scoop with a 7-10 inch fan evacuating air through that section. This is subject to change depending on how the engine sits in the bay and what my fabrication abilities will allow. (I've only ever done light bodywork. This would be a bigger deal than filling holes from a removed spoiler or luggage rack.)
That's a lot of work and expense for little to no gain in cooling......
A heat exchanger without airflow is a useless heat exchanger. I could put the exchanger under one of the existing vents, but then it isn't ambient air, rather heat soaked air, considerably reducing the intercooler's effectiveness by up to 50%. That's pretty significant on a turbocharged car. The other ducting is marginal in its gains, but oil cooler and heat exchanger getting fresh airflow is pretty significant.
What dobey explained is why I asked in the first place. That is precisely why I intend to duct air from scooped quarter panels to three places each. Driver's side will cup ambient air to engine intake, brake duct and low in the engine bay. Passenger side will duct to a heat exchanger for an air:water intercooler, passenger brake and low in the engine bay. Up top, I'm going to leave the side vents to convect naturally, but also add a rearward-facing scoop with a 7-10 inch fan evacuating air through that section. This is subject to change depending on how the engine sits in the bay and what my fabrication abilities will allow. (I've only ever done light bodywork. This would be a bigger deal than filling holes from a removed spoiler or luggage rack.)
Sounds like a good plan. The only thing I would suggest doing some testing on before you install it is the rear-facing scoop. Depending on the height, position, and whether or not you have a spoiler, the vortex that rolls off of the bottom of the rear fascia can cause air to flow into that scoop.
[This message has been edited by Steven Snyder (edited 04-11-2014).]
Sounds like a good plan. The only thing I would suggest doing some testing on before you install it is the rear-facing scoop. Depending on the height, position, and whether or not you have a spoiler, the vortex that rolls off of the bottom of the rear fascia can cause air to flow into that scoop.
This is the only part that has me weary. I need to see what my options are there. Scoop might not be the best description for what I'm thinking there. Center vent, but where the holes are, is currently up for debate. Body work + turbo is down the line, so I have some time to test before it becomes a concern.
Ferraris work the same way. Some models ( F-40 for ex) just have expanded metal for a rear body 'panel' to let all the hot air out the back. Plenty always comes in the bottom and the problem is getting rid of it.
The over the top scoops are useless.....but if you like the look, consider portioning the scoop so that the back portion of the base is a vent for the engine bay, and the scoop is ducted separately out of the exhaust flow airstream. Two ducts in a common housing as it were.
You can clearly see the airflow going forward in the notch area above the decklid.
The simulation doesn't model underbody or engine bay airflow, so that obviously interacts with the airflow over the decklid. It's possible for that area to become a stagnation zone if there isn't enough energy in the airflow exiting the engine vents.
You can clearly see the airflow going forward in the notch area above the decklid.
The simulation doesn't model underbody or engine bay airflow, so that obviously interacts with the airflow over the decklid. It's possible for that area to become a stagnation zone if there isn't enough energy in the airflow exiting the engine vents.
The stock spoiler helps with this though. It's much worse with no spoiler. I'd think a lip spoiler instead of the factory spoiler would be even better at helping to prevent air from going back up over the decklid. A Ferrari-style roof spoiler would probably also help to direct airflow down and out the back, but might not look nice, and would interfere with opening of the decklid.
I wonder how an Evo-style set of vortex generators (the black fin-things lining the back of the roof on the Mitsubishi Evo) on the roof would do? Not my personal cup o' tea when it comes to styling, but effectiveness? It's really just a thought experiment at the moment.
I wonder how an Evo-style set of vortex generators (the black fin-things lining the back of the roof on the Mitsubishi Evo) on the roof would do? Not my personal cup o' tea when it comes to styling, but effectiveness? It's really just a thought experiment at the moment.
On a street Evo, they're basically useless I think, and only there for style. Remember, the Evo body kit is adopted from the off-road rally car, and it looks like those fins would disrupt air flow, to prevent it sticking to the body as it flows over the rear of the car, which I think would reduce downforce. Maybe useful on a track Evo, but entirely useless on a street car when you want the rear to stick to the ground as much as possible. And given the questions you're asking about cooling, I don't think it would help at all.
Just think it out realisticly first. Are any gains you might get worth all the effort, expense and time you spend ?
Just a random make believe setup : You spend $500 for scoops, take say 30 hours of time, repaint modified parts after you make up a plan that also takes time. You get .3 mph speed increase and gain .2 mpg, and you drop engine bay temp by 2 degrees.......then decide if it was time well spent .... Now if you do it JUST for looks, and you like it...it is time well spent.
Lots of people, myself included sometimes, tend to over think or over complicate things. Theres a lot of stock Fieros with no added aero scoops that run as cool as theyre supposed to.
[This message has been edited by rogergarrison (edited 04-12-2014).]
Now if you do it JUST for looks, and you like it...it is time well spent.
