Aero mods and cooling

[Wimp Lo]

Wait until the RS hits the dealerships and take a look, I plan to do that. Vents there don't make any sense. One thing air doesn't like to do is turn 180° and that is what it would have to do twice to go through the IC and then out under the bumper.

Aerodynamics are not intuitive, especially passenger car aerodynamics where fuel economy and cost reduction can have a large influence on what goes on the car.

If you study race cars, there are good examples of pure aerodynamic devices. Kamm tails on the Cobra Daytona coupe, general excellence from the Toyota IMSA prototypes of the early 90s, NASCAR bodies for taped noses, air dams and general high speed aerodynamics for sedan shaped road cars. Once you understand how they work you will see how screwed up most production vehicles are and how they are broken.

 

[Levi1.0]

Love this thread. Been following it for awhile and joined the forum just so I could be a part of it! I drive a Fiesta 1.0 but this stuff is perfect for me too. I've been studying aerodynamics to improve the efficiency and performance of my fiesta. They go hand in hand.

Couple thoughts:
You can do a fuel efficiency test to see if the mods reduce drag. Find a clean stretch of freeway. Set cruise control and then reset fuel mileage gauge at a specific point of the road. Drive a set distance (longer the better) and record the mileage. Perform a mod and redo the exact test. Better fuel mileage equals less drag.

I think you guys already touched on this (i was having trouble understanding the post) but when your undertray created less pressure in the engine bay and more in front, do you think the effective airflow through the radiator has already been maxed out? Therefore trying to improve it with aero mods is pointless?

 

[Siestarider]

Love this thread. Been following it for awhile and joined the forum just so I could be a part of it! I drive a Fiesta 1.0 but this stuff is perfect for me too. I've been studying aerodynamics to improve the efficiency and performance of my fiesta. They go hand in hand.

Couple thoughts:
You can do a fuel efficiency test to see if the mods reduce drag. Find a clean stretch of freeway. Set cruise control and then reset fuel mileage gauge at a specific point of the road. Drive a set distance (longer the better) and record the mileage. Perform a mod and redo the exact test. Better fuel mileage equals less drag.

I think you guys already touched on this (i was having trouble understanding the post) but when your undertray created less pressure in the engine bay and more in front, do you think the effective airflow through the radiator has already been maxed out? Therefore trying to improve it with aero mods is pointless?

I have not tried the fuel economy method, coast down testing is faster and I can run static pressures at same time, but if you have some, I would love to see.

My take is when full size undertray was mounted, air flow through heat exchangers was restricted, hence higher pressures in front and lower behind heat exchangers.

Minor adjustments did not change it.

Then cut rear corners off and aero improved a lot, not as much as 2" air dam extension did without tray, but better than OEM air dam at stock height. Pressures in front and rear of nose came back closer to stock.

That Masters Thesis I found indicates that unrestricted pressure drop through our car's radiator and A/C condenser combined should be about 1.5" H2O at 80 mph. Extrapolating his SCFM curves and assuming our intake diffusers are reasonably efficient.

I was thinking about opening up more nose area, but RS looks like its as little as ours. So that is on hold.

On the other hand, look at our car's engine bay from below, there are two reasonably open paths for air along each side of lower half of engine bay, with crankcase dividing them and nearly touching tray. Both dump into wheel wells and exhaust tunnel behind WW's. Both have cross-sections that, while dirty due to obstructions, are larger than our intake areas. So I believe our heat exchanger air is going those routes. I also believe undertray helps make those two areas act more like ducted diffusers.

If so, question for cooling is how to make them dump down beside or behind tray into faster moving, lower pressure air without too much turbulence.

RS has even more of the rear corners cut off than I do, plus whatever the additional ductwork in undertray does. We safely assume the NACA ducts pick up air from below tray and let it into lower engine bay. Hard to say exactly where, and exactly counts for those.

I found BMW on several new cars using vents where our fog lights are to vent nose air straight through to front wheel wells. Claim that increases aero efficiency. Looks like RS is doing some of that too.

So, back to pondering next mod, don't want to cut it up too fast and make it junk, or too slow and waste experiment time.

 

[Wimp Lo]

How did you measure the front and rear pressure? Was it differential?

A splitter stops air from going under the car but the air has to go somewhere, the grill is the closest place, I expect higher pressures there. With less air under the car, pressure is going to drop there. Higher differential pressure through the radiator means more flow, I bet there is lots of radiator air flow happening and low pressure in the engine compartment is exactly what you want.

That pressure drop across the heat exchanger is something you can get by taping the grill opening after you have sorted out the splitter and undertray but the target we need to hit is based upon how much cooling is needed, it won't be the same as the thesis because that is based on a steady state cruise, not full throttle acceleration and the radiator area is different. Different core configurations would create different pressure drops too.

Don't worry about high pressure at the grill, it's good.

 

[Hijinx]

I have little idea about what you guys are discussing, but I like it. Keep going.

 

[RAAMaudio]

The RS front drivers side duct is to help cool the transmission and or battery if still located in the front of the car.

The NACA ducts are to draw air through the radiator and out the back of the engine bay and will help cool the heat from the cat and cool the steering rack.

The effect of introducing higher speed air flow at the middle and rear of the engine bay will lower the pressure behind the coolers thus pulling more air through them.

I had a nice discussion about this with somebody that understands it from lots of experience and then modified my undertray to take advantage of it, as posted a few times but now I am sure, no testing, seems to work very well so far.

 

[Sourskittle]

I have little idea about what you guys are discussing, but I like it. Keep going.

Ditto... Let me know when you guys figure it out and I'll stand on the shoulders of other to reach the cookie jar, lol.

 

[jayrod1980]

Not sure how much this helps but enhanced pics to show a bit more detail...

View attachment 8440

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Not all that helpful, but seeing these pictures made my pants tight. That's really neat what they did. I'd love an RS and I knew about it before I built my car... could have put a deposit on one, but the Fiesta is more practical for me. Ugh. Still lurking here... more cooling and better fuel economy from Aero are always welcome. Still amazing Rick can get 41 on the highway with that turbo... but drafting an RV probably helped.

 

[Siestarider]

Perusing venting a while back, premade and properly dimensioned plastic NACA ducts are cheap. Should be easy to install in undertrays. Whole 'nother area to explore, and best part is if not happy with NACA ducts in undertray, just tape them off from beneath on creeper and they are functionally gone.

Tricky part is where to place them, introducing higher pressure zones into lower engine bay is likely to make turbulence hash out of heat exchanger flows from front if not properly placed. I am thinking just behind crankcase, like RS. One day out of plausible options to improve cooling with undertray, next day RS pics come out, now too many options.

 

[RAAMaudio]

I have posted these or at least one of them on a thread or two but not sure about here. I wanted to use NACA ducts but had none on hand and was in a rush to get something done so experimented a bit and wanted to bring in air to the Cat and DP area to help keep them from overheating the steering rack, brake and fuel lines as well as shifter cables.

Not the best pics but it has a nice smooth curve and a section on the 2 point brace/rear undertray mount to help direct the air up to the area I wanted it to go.

No testing done except seat of the pants(butt dyno if talking about power) but I never see high oil or water temps and the car is far more stable at speed with the undertray than without.

Also I had plans to add more material to complete the inverted wickerbill effect like the 2 point brace does.

I hit something on the road and bent the mount and messed up the drivers side skirt so have to make a new part and once done with the latest turbo swap will see about some actual testing.

 

[Levi1.0]

When RAAMaudio was talking about using NACA ducts to bring air into the engine bay, I was envisioning the air going up into the bay and creating positive pressure. But after looking at his pics again and the RS pics, the air doesn't go "up" into the bay, but rather the air stays parallel with the bottom of the car. So that makes more sense that it can cool components and also the high speed air should draw more air out of the bay. As a added bonus the trailing edge of the NACA ducts/undertray now becomes another spoiler/wing that can be used to adjust airflow.

Wheel wells are generally low pressure so venting air there seems to be a good alternative to cutting hood vents. The air then just goes around the side of the car instead of over. But wheel and tire aero is a whole 'nuther story that I haven't looked into much yet.

I haven't done any fuel mileage tests or mods on the fiesta yet. ...busy and bad weather... But when I was testing electrical efficiency on my '05 Focus ST, running with the headlights on, it consistently cost me 3mpg's! :O

 

[RAAMaudio]

I had a very expensive C6 World Challenge body, wing and undertray for a C5 Z06 race vette I bought to rebuild into a faster car. The undertray was full length and the corners you cut out were still there but it had two very large bent NACA ducts from the front back towards the mid to rear of the front tires, openings at the end 3 sided, no bottom, around 4-5x12" or so in size. 50 hours of wind tunnel testing into the design.

I wanted to copy that as close as I could for this car but to much stuff in the way

 

[Siestarider]

I ordered 2 NACA ducts from Summit today, they are 10" x 6" and designed to connect 3" hose. After seeing those pics of RS undertray, lots of new applications via undertray come to mind. Looking forward to trying some.

 

[Sourskittle]

Ole my stars Kevin !! I hope you plan on selling something when your done, lol. Send me templates, I'll build them. No one will argue if they work or not because on you, Rick, and Wimp are smart enough to know what the heck your talking about, lol.

 

[Siestarider]

Coming soon. (siestalator modified race/DD aerocooling undertray) Rumors say it will have Cyborganator alternator option. (see Track Battery thread)

Offered in stealth material that defies all speed measurement devices, like steroids for your heat exchangers, doubles top end and so quiet it puts drivers to sleep. Ok, leave that last part out.

 

[Siestarider]

On a more interesting note, Google JDM Yard Honda Civic Time Attack. ahttp://www.worldtimeattack.com/index.php/jdm-yard-civic-now-a-serious-contender/m

Thinking this is current state of race art for aero that could be relevant to Fist.

At least, its a hatchback, undertray aero is limited to fore of front axle and rear of rear axle, and the front and rear within about 8" of OEM bumpers are "open".

I read the rules, despite its radical appearance front and rear, its still a Honda hatchback. And it absolutely trashed all the GTR's and everything else in its class in 2015.

Engine is not civic, but its Honda.

Sure wish we had a look at the front undertray. Does show enough to indicate how a rear diffuser would work on our car. Cool wings and splitter too.

 

[Levi1.0]

I found it interesting on the time attack Honda that they purposely routed the exhaust down into the rear diffuser.
Wide open, cars pump a lot of air out the exhaust. That exhaust can be used to fill in the wake behind the car, which reduces drag. Almost like a an invisible boat-tail. So why did they put the exhaust down into the diffuser instead of easily angling it up into the gap above the diffuser? Hmm...

Also, cars inhale a lot of air when wide open. So your intake design can affect pressures in different areas. So a pressure reading at a low load cruise could be different than when you're wide open at that same speed.

 

[Wimp Lo]

I haven't looked at that car but if done properly, the exhaust can act like it is feeding a venturi and pull more air through the diffuser which will enhance the low pressure area under the car, fill the wake with more air and possibly smooth out the turbulence in the wake with less pressure differential several feet behind the car.

Ground effect tunnels and diffusers are awesome if you have the space to implement them well. Production cars usually don't have the space or the implementation.

A front wheel drive time attack car is the perfect place to look for inspiration if it actually has effective aero. Rally cars have pretty good aero but they are designed for lower speeds and higher ground clearance. GRC cars might even have some aero designed to make them fly straight...

 

[RAAMaudio]

I built a car with a huge diffuser and exhaust outlet dumping into it but was advised to consider what this might do during off throttle, on throttle, part throttle situations, could upset the grip enough to be of serious concern. I ditched that idea and ran the pipe close to the end of the diffuser instead, it had a Vband coupling right where it tipped up at the inlet to the diffuser so I could swap the muffler or straight pipe easily depending on dB restrictions on track or when I took it on the street on occasion.

We were working on a tune to make it bark and fart some flames on deceleration just for fun as well

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FWD aero, Chirs Rado TT Scion tC on left, AWD on right.

My far more humble tC, TT, autocross, sound quality audio competition, street on occasion....

 

[Levi1.0]

I'd get that front wing ripped off by somebody as soon as I got onto these Utah roads...

Anyone here try working on flat floors and rear diffusers on the fiestas? Might help the front undertray be more effective with cooling.