Aero mods and cooling

[Siestarider]

Yep, I pulled the extended air dam off today, will tape off all four vents, run a new stock aero baseline coast down, then remove fog vents tape first, then hood vents, testing each.

I may have forgotten to mention I added reinforcement behind the extended air dam, so its behavior is very different now compared to its former ability to "bend" with speed. A fixed air dam should be mounted further forward, maybe integral with a splitter, so the high pressure bubble is forced up into the intakes and around sides. Mounting a stiff air dam as far back as I did using the stock lip probably also creates lift in front, undesirable for tracking. I was really surprised to loose more than 10% aero efficiency, so best to follow Levi's counsel, back to basics and evaluate each variable in turn.

If I can get this sorted next few days, maybe can experiment further on track.

 

[Dustys318]

I've got these ordered. I think I might pull the insulation/sound deadening off for track days and not cut it -- rather than cut the material away under the vents. It might provide a little bit of shield from heavy rain. I'm not too concerned about water intrusion (car is garaged so does not sit out in the rain usually). However, in the winter, it does rain most days, so a little bit of cover should be enough.

Looking down into the driver's side vent you can see the fuse box. I've gone through car washes and drove through rain, never any issues. But I am moving the battery to right rear of car, moving the fuse box next to PCM and coolant tank to factory battery location. Doing this will reduce air flow restrictions between the grill and vents. I'm also going to make some rubber flaps on the driver's side radiator shroud something like the factory plastic ones on passenger side. Then seal up all openings to force the air through intercooler, oil cooler and radiator. It'll increase drag but aid cooling. 100°+ heat is coming soon to us here in El Paso...

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[Siestarider]

Getting ready for logging, vents taped and digital manometer ready

Hose adjusted after pic to be more perpendicular to assumed air flow.

Loaded up ready to log

Started over today with stock air dam, all vents taped off. Ran coast downs from 85-40 mph two ways each test. First baseline average coast time 49.2 secs. Baseline manometer pressure at hood vent -0.2". slight negative pressure measured underside of hood before, so all seems good.

Pulled tape off fog vents that lead to CMB brake ducts. coast down 47.9 sec. Manometer -0.2". Who would think opening 3" vents at fog light level would affect aero? Good news is it proves brake ducts are pulling air from front of car, adding a little drag.

Pulled hood vent tape off, coast down 48.0 sec. Manometer -0.3" Pressure drop interesting. Pretty much has to mean air is leaving engine bay via hood vent (plus I could feel it with my hand out the window).

Added a strip of rubber weather gasket to hood vent trim. Still less than 1/2" proud of hood surface. WRC pics look to me like more than that, but I used what I had.

Coast down 46.8 sec. Manometer -0.4" Ran up to 90, manometer dropped another 0.1" to -0.5" This is about the same spot I measured pressure on hood exterior at -2" or a little more. Theory says if air is added to an existing low pressure zone, it could result in improved aero. Dusty reported this with his hood vents, but very different from my home made version. Maybe mine are adding to turbulence instead of making it better.

So, lost maybe 5% aero efficiency with one lipped hood vent and three regular vents vs stock no vents. Wish I had a way to measure heat loss with this rig. Have to track to learn more.

I am thinking adding a higher air foil around hood vents is worth looking at, but with no method of measuring heat lot vs aero lost, cannot tell. However, if pressure drops more and aero does not degrade further, could be a good avenue.

Going back to air dam experiments, I am amazed that just stiffening the 2" extension produced that much drag. Might have to give Ford some credit for getting aero right. Not many cars this light are as stable at speed as our Fist.

 

[Levi1.0]

Thanks for that info and pics. Interesting data.

Are your fog vents completely sealed to the brake ducts or does some air get into the engine bay?

 

[Siestarider]

Thanks for that info and pics. Interesting data.

Are your fog vents completely sealed to the brake ducts or does some air get into the engine bay?

With new air boxes behind both vents, brake cooling hose to CMB duct plates is tight all the way, no leakage, both sides now. I posted some pics on brake cooling thread. We have another experiment going with brake ducting and air flow into rotor hubs, I need to check weather and then paint rotors with temp indicator before Sat.

I just read this whole thread for first time, realized I should test pressures in front and behind HE's again to see what the hood vents are doing to pressure differential across radiator and IC. Also most of what I have tried has failed to produce significant improvements in either cooling or aero. So hoping hood vents test well this weekend for cooling, since they apparently hurt aero a little.

I believe most or all of the benefits of my air dam extension experiments would be achieved simply by lowering car 1". I have been putting off suspension mods while I learn to drive. But the urge to put on BC coils with Swift springs is growing, then I could play with height, rake, weight balance, etc.

Undertray is trickier, I think waiting for better understanding of what Focus RS is doing is better than more experimentation in this direction at present. So many variables, so little time.

 

[Wimp Lo]

The WRC vents have a C shaped profile which directs the slow moving boundary layer air around the vent and the high speed laminar flow over the vent to suck out engine compartment air. It is kind of like a miniature inverted splitter.

The lip you have might be creating a large vortex behind it which could hurt drag a fair amount.

Once you have the hood vents pulling out enough air, that is when the undertray is going to pay off because you will be able to extend it back and let less air under the car.

I keep saying this but a nice low mounted splitter that extends forward of the bumper and forms the bottom of the undertray will be the piece to bring it all together once the hood vents are working good.

 

[Bluedrank]

Not sure if this has been posted. But Ford's been playing with a souped up focus st with some aero mods lately. Maybe there's something in the spy shots that looks useful to you guys.

http://www.carscoops.com/2016/04/is-ford-working-on-hotter-focus-st280.html

 

[Siestarider]

Not sure if this has been posted. But Ford's been playing with a souped up focus st with some aero mods lately. Maybe there's something in the spy shots that looks useful to you guys.

http://www.carscoops.com/2016/04/is-ford-working-on-hotter-focus-st280.html

Good find. Looks to me like Ford drops the air dam behind IC and adds a splitter and undertray per Wimp's comments. Plus slight changes to nose aero that may enhance splitter and canards usefulness. Wish I could tell if fog lights have functional vents.

I must have missed the larger brakes on Fist 200, maybe we will have a factory option after all?

 

[Wimp Lo]

The info about Fiesta ST200 is kind of hard to decipher. I think the parts about brakes and suspension were copied from Fiesta ST press releases where they compare them to standard Fiesta pieces.

In my mind if they changed all that stuff, that would cost almost as much as the original Fiesta ST development, I don't think they intend to sell enough Fiesta ST200s to recoup a cost like that.

Any way, I'm skeptical until I see official specs or new part numbers.

 

[Levi1.0]

The WRC vents have a C shaped profile which directs the slow moving boundary layer air around the vent and the high speed laminar flow over the vent to suck out engine compartment air. It is kind of like a miniature inverted splitter.

The lip you have might be creating a large vortex behind it which could hurt drag a fair amount...

I understand what you're saying about the vent creating turbulence but can you elaborate on how Siesta's vents are different from the WRC cars? Other than being shaped a little different, I don't see much of a difference. The rally car's vents are bigger, so if anything, it seems they would make it harder to have smooth airflow over them.

 

[Wimp Lo]

If you look at the flow of air over a surface, unless you have a constricting duct geometry, air near the surface will be moving with a velocity close to zero relative to the surface. The further you get from the surface, the closer you get to the speed of the flow.

This slow moving air close to the surface is called a boundary layer.

Now for some ASCII art:

>>> >>> >>> >>> >>> >>> >>> >>> >>>
                  _____
>>   >>   >>   >>      |
                       |
>     >     >     >    |
------------------------------------------------

The arrows represent air flow, more arrows means faster flow. The lines represent the body surface and leading edge of the duct.

The slow moving boundary layer gets trapped under the lip so it has to turn to the side rather than go up and over. Since the air is slow moving it does not take a lot of energy to make that turn. Without the lip, that air would flow up and over the vent and disturb a lot of the high speed air creating turbulence and drag.

The design of a duct like this is determined by the thickness of the boundary layer (for the height) and how far you have to push it to the side (how far the lip extends forward).

 

[Wimp Lo]

From another thread:

Project RX Episode 1: Design and Development

Published on Apr 27, 2016 - Ford Performance

Introducing "Project RX": A behind the scenes look at the design and development of Ken Block and Andreas Bakkerud's Ford Focus RS RX race cars...

The Ford Focus RS RX was designed to be the ultimate rallycross vehicle. Take a look at the process that Ford Performance engineers, M-Sport, and Hoonigan Racing Division drivers Ken Block and Andreas Bakkerud went through to get the vehicle optimized in both performance and design.

https://www.youtube.com/watch?v=KG6E24ixFEY

[video=youtube;KG6E24ixFEY]https://www.youtube.com/watch?v=KG6E24ixFEY[/video]

If you look at the splitter design you will see it extends far forward with an air dam mounted at the very front.

That car is designed to fly and probably for rough landings which I think is why they use an airdam instead of just a lower splitter.

There are many ways to skin a cat but when its all variations on a theme, they probably found the right theme.

 

[Levi1.0]

Ahh, I was a little confused about what you meant about the vent having a C shaped profile but makes sense now. I've noticed that shape of the lip in different pics. Couldn't figure out why. So thanks for that explanation.

So next question is: how thick could that boundary layer possibly be being that close to the front of the car and partially behind the headlights?

 

[Siestarider]

Ahh, I was a little confused about what you meant about the vent having a C shaped profile but makes sense now. I've noticed that shape of the lip in different pics. Couldn't figure out why. So thanks for that explanation.

So next question is: how thick could that boundary layer possibly be being that close to the front of the car and partially behind the headlights?

Pretty thin, when I ran yarn tests with gopro, the only indication of low pressure on hood was yarn was not stretched, just aligned with airflow. High pressure areas stretch yarn tight to body. My guess is less than 1/2" where hood vents are.

Spent some time on that video, pausing over and over. Looks like a lot of good info, but frame by frame, its pretty general and colors may be misleading. Note the hood vents in this application do not have air foils (yet).

 

[Wimp Lo]

You spent a lot more time on that video than I did.

There was one CFD visualization of the side of the car but it didn't seem interesting enough for me to freeze frame...

I mainly like the link image with the splitter and air dam front and center.

 

[mercdank]

Bump! Any further developments in the aero and cooling game? Do vents work or not? Are undertrays/skid plates good for aero and cooling?

I used to have the VT Big Mouth and have since changed to the 2JR cowl intake. I never patched up the hole in my radiator shroud so there is basically an open path from the grille in through the hole in the radiator shroud and into the engine bay via the open hole from where the stock intake box used to be. I am not sure that, combined with the open bottom of the engine bay, that this hole is helping me with my cooling or aeros. Any thoughts? I will make a video about what I am talking about tomorrow.

Has anyone removed the active grille shutters? Mishimoto mentions they did this when they did their oil cooler R&D. I don't think our cars have this though I could be wrong.

 

[Siestarider]

Bump! Any further developments in the aero and cooling game? Do vents work or not? Are undertrays/skid plates good for aero and cooling?

I used to have the VT Big Mouth and have since changed to the 2JR cowl intake. I never patched up the hole in my radiator shroud so there is basically an open path from the grille in through the hole in the radiator shroud and into the engine bay via the open hole from where the stock intake box used to be. I am not sure that, combined with the open bottom of the engine bay, that this hole is helping me with my cooling or aeros. Any thoughts? I will make a video about what I am talking about tomorrow.

Has anyone removed the active grille shutters? Mishimoto mentions they did this when they did their oil cooler R&D. I don't think our cars have this though I could be wrong.

Cooling is improved by increasing the air pressure drop across heat exchangers. You can increase the positive side by closing all the front end cracks and openings around the radiator and I/C so no air pressure leaks down. I am skeptical of opening up the grille more, serious fast cars do not have big radiator openings, bad for Cd and plenty of pressure at speed available from stock grille.

WRC type hood vents help but not a single fix in reducing air pressure behind the heat exchangers. Mine work (I can feel the heat holding my hand out the window) but I have not added the "lips" yet, so should improve when I do.

My experiments with undertrays were mixed. A full undertray back to axle line hurts back side pressures, opening up sides at wheels improved back side pressure some vs stock, but again not greatly.

I am going to try an oil cooler in the fan shroud where those flaps are. My thoughts are that better to use a shrouded oil cooler with hotter air than an unshrouded cooler in front of radiator. Just an experiment.

I am also planning to test a splitter with an air dam hanging from it. Theory says that should produce the lowest pressures behind the heat exchangers.

Just have not had time to more than track whenever I can, fun has priority over research.

 

[scotman]

Getting ready for logging, vents taped and digital manometer ready

Hose adjusted after pic to be more perpendicular to assumed air flow.

Loaded up ready to log

Started over today with stock air dam, all vents taped off. Ran coast downs from 85-40 mph two ways each test. First baseline average coast time 49.2 secs. Baseline manometer pressure at hood vent -0.2". slight negative pressure measured underside of hood before, so all seems good.

Pulled tape off fog vents that lead to CMB brake ducts. coast down 47.9 sec. Manometer -0.2". Who would think opening 3" vents at fog light level would affect aero? Good news is it proves brake ducts are pulling air from front of car, adding a little drag.

Pulled hood vent tape off, coast down 48.0 sec. Manometer -0.3" Pressure drop interesting. Pretty much has to mean air is leaving engine bay via hood vent (plus I could feel it with my hand out the window).

Added a strip of rubber weather gasket to hood vent trim. Still less than 1/2" proud of hood surface. WRC pics look to me like more than that, but I used what I had.

Coast down 46.8 sec. Manometer -0.4" Ran up to 90, manometer dropped another 0.1" to -0.5" This is about the same spot I measured pressure on hood exterior at -2" or a little more. Theory says if air is added to an existing low pressure zone, it could result in improved aero. Dusty reported this with his hood vents, but very different from my home made version. Maybe mine are adding to turbulence instead of making it better.

So, lost maybe 5% aero efficiency with one lipped hood vent and three regular vents vs stock no vents. Wish I had a way to measure heat loss with this rig. Have to track to learn more.

I am thinking adding a higher air foil around hood vents is worth looking at, but with no method of measuring heat lot vs aero lost, cannot tell. However, if pressure drops more and aero does not degrade further, could be a good avenue.

Going back to air dam experiments, I am amazed that just stiffening the 2" extension produced that much drag. Might have to give Ford some credit for getting aero right. Not many cars this light are as stable at speed as our Fist.

I weather stripped the engine compartment perimeter on the 2011 I did this to. I experienced a low frequency humming sound when passing large trucks. I found out that the hood inner structure needs to be sealed up. All those cutouts underneath got caulked. I used gap filling expansion foam in a can to seal the voids around the exit cut holes. It really boosted the cooling effectiveness​.

 

[TyphoonFiST]

Why not a NACA style Duct?

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[Siestarider]

I weather stripped the engine compartment perimeter on the 2011 I did this to. I experienced a low frequency humming sound when passing large trucks. I found out that the hood inner structure needs to be sealed up. All those cutouts underneath got caulked. I used gap filling expansion foam in a can to seal the voids around the exit cut holes. It really boosted the cooling effectiveness​.

That sounds a capital idea. I may remount hood liner to see if I can tell any difference. But there will still be a couple voids directly next to bonnet vents unless liner can be glued over them. Good tip, thanks.

Typhoon's question, NACA ducts would be mounted where high pressure (above ATM) areas enable duct to collect air flow without distorting surface flow. My vents are designed to extract air, not in.

Manometer tests inside engine bay suggest its all negative at speed, more negative the lower you go in the engine bay. But engine bay turbulence is high compared to flow over the exterior body. NACA ducts work best in places with laminar flow and high pressure. The only places on bonnet that works for would be for letting air into engine bay, opposite of my goals to reduce pressure behind heat exchangers.