Hi all,

I'm a new member, so go easy if you will. Anyways, I'm currently a university student working on a class project for a professor/teacher, which just so happens to entail his modded 914 (see more here).

In a nut shell, he has already bought a front-mounted oil cooler for the 914, but does not know the optimal shape/size of the holes in the front bumper/valance area and the front floor in order to provide the right amount of airflow to the cooler, yet still preserve as much aerodynamics and lowered drag. He has tasked us to figure this out (using Solidworks/Flow Simuation, and a real-life water channel experiment using a 914 scale model), and suggested this forum for advice.

Anyways, has anyone done/looked into anything similar for their car, especially modifying the front fascia area to increase/promote better airflow into an radiator/cooler, and what kinds of results/consequences you noticed? It doesn't even have to scientific at all, I was just fishing for different ideas of how some drivers may have modified their cars especially to promote aerodynamics and/or better airflow in the frontal area.

This is mainly an autoX car, so huge ass fins or wings won't be that important. I'm more looking for slits or opening modifications to the bumper/fascia.

Thanks all for your help.

not sure if this what your looking for , 20yrs ago.

In is easy.
You can get no more air in than you can get out.
Figure how you're gonna exhaust the heated air.
For a variety of reasons, conventional wisdom dictates the exhaust must be bigger than the intake.

The Earls Supply website (hint: they are a Holley company) has a lot of good information on airflow requirements.

For extra credit, reference Carroll Shelby Smith's 'Prepare To Win' which has a lot of excellent information on ductwork design.

A cynic would observe that a front-mounted oil cooler is silly on an AX car since oil probably can't heat up enough in 60 seconds to need one, and if it does - the car's not moving any more at the end of the run. Informing one's instructor that he's wasted a buncha money on needless parts may not be the fast-track to a good grade, even if it is the correct engineering answer...

(BTW -- )

(Thank you for the correction Terry)

Hi Backdraft,

Thanks for joining and sharing your project info on the aerodynamics of the 914.

I've done a lot of Autocrossing (some of it with my first STOCK 914) and agree with Artechnika about NOT mounting the front oil cooler. I viewed the video of the tufted car and it sounds as though it is DEAD stock, with no need for additional oil cooling other than the one already on the engine. Thus, it seems the best aero answer is keeping the nose of the car smooth and free from openings to promote laminar airflow. However, if this is an assigned project for the experience of doing the analysis, carry on!

With respect, a correction: the author of the Engineer, Drive, Tune, Prepare and Screw TO WIN books is the late Carroll Smith: An engineer first and great race engineer to-boot. I keep all of them as a reference library and recommend them highly.

Now I have request for some of your help: I have a V8 conversion car and am VERY interested in the airflow from the rear window to the back of the car. While the car was designed around air flowing INTO the engine cover, I am flowing air from under the car and OUT the top. I'm very interesting in:

-Can you share any more Solid Works output, photos of tufting or the like showing in greater detail the airflow over the rear trunk area and engine cover?

-Your analysis work is at very low speed as in autocrossing, will airflow characteristics change at 100 MPH? If so how?

-Do you have anything that would indicate the airflow for my application?

-What could I do to AID the up-and-out airflow?

-Am I bucking the cars design my trying to vent to a higher than desirable pressure area?

Thanks for any feedback,

Terry

You are absolutely correct.
Brain fade on my part.
That's what I get for trying to remember stuff while taking a break from mowing the lawn...

Great books all and yes, I've got 'em - even the little pocket reference...

If you have air deflectors on the underbody (I don't know when they started that) remove them.
If you can add a wickerbill to the trailing edge of the top and outboard edge of the sail panels, they'll help reduce the pressure at the screen.

I don't think the engine lid area wants to be a high-pressure area, which is why the underbody flaps were introduced - to help extract air out the bottom and increase the pressure differential. It's a sorta-effective intake for the air-cooled cars because we have (relatively) huge fans spinning at high speeds sucking air in. The /4's squirrel-cage fan runs at crank speed, but that /6's axial fan runs about 1,8x crank speed...

I thought I saw a Subie conversion actually implement underbody scoops. I thought that was a bad idea but for an AX/track car you might get away with it. I think it'd suck up too much water, trash, and grit to make it a good everyday-driver method.

I did some airflow testing with yarn and dirty oil, but it didn't tell me anything that wasn't already known.

Hey ArtechnikA,

Yup, we're on the same page: I removed the underbody flap long ago. To deflect air upward, I my own air dam back in the middle of the engine bay that extends
down 4". When I drive the car, I come back with dust and weeds all over the engine and a heavy dust layer on the rear trunk lid. So things appear to working as I want them too...but I could look at adding the scoops you mentioned.

I also made my own fiber glass side scoops to pull in more air to the engine bay.

However, when I tufted the car, I was surprised to see that once the air flow gets around the sides of the roof, back about mid trunk lid, air starts flowing FORWARD to the engine bay. If you take a look at the professors web site, there are a number of computer created drwgs, along with a video of the prof's tufted car showing the same air flow patterns.

Additionally, I was expecting a BIG vortex coming off the roof of the car creating what I hoped was a BIG low pressure area. NO JOY: my tufts told me the vortex was only about 5" in diameter and the air smoothed out only 18" back from the roof. So I don't know how big nor how much drop in pressure exists in the volume
above the engine cover. Even a 2"roof spoiler did little to increase the vortex.

So I'm left with less real world data than I would like and that's why I asked the engineering student for some more info on that area of the car.

What a great way to do a college project: you MUST work on the aerodynamics of a 914!! Ya' Gotta' Love It! I hope he is.....

Terry

Lol thanks Terry, but then you realize you are being graded on this . Also CFD theory is quite difficult to grasp.

Anyways, thanks for your replies. Just to clear a few things up:

The reason he's putting an oil cooler in it is because his engine is modded (even though it might not seem apparent from his site) up to almost 120 hp according to the dyno graph, and he's running temps of up to 250 F after a hard run at an autoX. Also, I didn't mention this but the autoX he runs it at is Qualcomm Stadium in San Diego (I'm studying Mechanical Engineering @ UCSD), so, combined with the hotter weather, as well as a tighter and harder-running track (60+ secs for a lap is normal for this track, unlike the 30-40 you usually see), it doesn't come as a surprise that the engine is running that hot. In the future, he is also planning to drop a 6 in there too.

As far as the airflow characteristics towards/over the rear of your car, as you may have noticed the projects already displayed on his website were done by previous years' students, so unforunately I do not know the complete results/conclusions they deducted from their experiments, except what is already seen in the poster PDFs. I'll try to look at their research papers when I obtain them.

Anyways, for our project, we are only looking at how modifications to the front fascia/underside will affect our airflow through the front trunk, because that will be where the oil cooler will be mounted. That is why I was asking if you or you knew any examples of 914 projects where the front valance/bumper area was modified to increase airflow to the trunk bay, so we could model it in CAD and do airflow simulation for these different configurations and intake/exhaust sizes. IE. Something like this, which is obviously not stock bumper:

Wow, that's wild. I like it

Isn't that the standard AIR kit?

Sorry, I ain't buyin' it.
Find out how many mouse nests he's got over his stock cooler.
Or why else it's not working.

120HP ~= 10% over stock.

I've driven the AX courses there. Before it was Qualcomm. Before it was Jack Murphy even. I know the area (lived there 20 years). I have driven 120HP+ cars there...

I've also driven 75-second AX courses in 110ºF ambient in the high desert (Reno, Winnemucca, Hawthorne NV...

If you're seeing 70ºF oil temp rise in 60 seconds, something is wrong...
A front-mounted cooler won't do squat once you pull off the course.
I expect you're plumbing a thermostat, so it might not even help you much when it's on the course...

OK, but you're looking at AN-12 plumbing for that (AN-16 better...) so either what you have is WAY too big now or you're back to Square One should that day come.

You need look no further than the 914.6 GT cars. ~210HP. Little bitty opening into the front bumper/valence, exits through trunk floor.

They didn't worry about airflow exiting under the car and they were driving on the Mulsanne Straight.

With limited HP, drag is a factor. Air you can't evacuate is drag. Concentrate on the exit.

For a dedicated track car, exhausting up through the trunk lid works well. This kind of bodywork mod is not permitted in most classes so Step Zero is always: Read The Rule Book. But it's efficient and can contribute to improved downforce. Not that it's a big factor in a stock-ish car.

Hey Backdraft,

Thanks for your reply, I saw what was on the Prof's site, but, of course, wanted MORE!!

I understand in spite of what your Prof THINKS about the oil cooler, YOU MUST work with it! It's great preperation for working in the Real World after graduation: can you say BOSS? ....Maybe the prof should take a course on Thermal Dynamics?

I'm still envious of your study project as there is nothing like real world testing and finding results with a science (Black Art?) like aerodynamics.

For GRINS, I attached a couple photos of the front of my car. With some 500 HP,
I am NOT concerned with a low CD and look to pick up some down force.

You'll note the flexible air dam below the splitter: that was intended to increase the low pressure area under the nose to aid the trunk-bottom exhaust from the radiator. However, I'm currently in the middle of change my cooling approach and have repositioned the radiator to exhaust out the top through the hood. I've removed the air dam and hope the increase airflow under the car will aid in engine cooling. Ya', I know, it's a water-cooled engine, but during building this project I learned that the Chev is still 30% cooled by air over the block.

Enjoy your project and please update us on your findings! 914s have been around for 40 years, but I've never heard of anyone doing a study on the CD of the nose.

Best,
Terry

Body kit is cool, but we've seen it.

You reference 120hp. An efficient 120hp type 4 doesn't need external oil cooling and associated ducting. Sounds like your team is behind the curve.

I applaud what you are doing, but be sure you explore what has already been done. How about a TIV with nearly 200 hp and tq with stock cooling?

Research first so you don't reinvent a wheel, but rather build on it. Further and break ground!!!! Looking forward to what your team adds. And know you've got huge resources behind you here.

Add a front big, flat, horizontal front splitter, model how much more air is shoved into the cooler, and how much less goes under the front trunk. Maybe you can even determine the achieved downforce, which is the real reason to add this. Play with splitter length, width and how far it extends under the front end, maybe even create some channels into the middle from the sides or side wings on it??

Of course, really adding a splitter means balancing it with a wing and overcoming more drag, but it would make a good modeling exercise.

Adding the cooler adds a bunch of messy ballast, so if it were my car I would look to other solutions for cooling, and consider a cooler mounted closer to the engine.

Have fun! The AIR body kit is rad

Something isn't right if he's running 250 temps after a AX run ...


The blue 914 up here that is usually TTOD at the local AX does not even have a cooling fan anymore!
Or engine tin. Or blower housing. And it has more than 120HP.

Yeah... My 2056 would get warm with two drivers at El Toro and long courses running back to back, but not that hot. Now that I have an external cooler it is perfect.

I'd check timing and AFR. Mine got even better as I dialed those in. I still need the cooler for the track though...

Guess it depends on whether youre talking 120 WHP or crank HP on a dyno. Type of compression etc. I could see a car over heating at Qualcomm if it didnt have an external cooler. A hot run up one of the hilly sections could definitely bring the heat up.

For reference, my head temps when racing are usually at 300F, it's just my oil temps that creep up lap after lap. I'd be curious what the head temps look like on the car.

Maybe whoever build his motor left out the cooling flaps. Wouldn't be the first time that happened.

Without the cooling flaps installed, there's NO air flow to the stock oil-cooler ...
Andy

@ Art: Isn't 120 hp an increase of around 50% over stock (80 hp), or is my math wrong? Anyways, I sort of see your point that 120 hp is still not very much for this type of engine (if run efficiently), but I'll try to clarify with him why and where he's exactly seeing these types of temps.

Since neither you nor any of the information on the original information link page list a year or model, I went with the 2,0 in part because there are no cooling system changes from the early cars to the later ones. So the 80HP cars have the cooling system used in the 100HP cars.

I had remembered the 2,0 HP as 105, but even if it's only 100HP and a 20% increase, the point was the same - 120HP is not enough to increase the oil temp of a 914 70ºF in a minute... (Which assumes it starts off at 180ºF, which can be a challenge for an idling engine even in 100ºF ambient. If you've got 180º at idle, there is definitely something wrong.

I'd start with making sure the temperature gauge is calibrated...

BTW, in case it wasn't clear before, I'm not trying to dump on your project, which sounds like great fun and a wonderful opportunity. But I do engineering for a living and I see people all the time trying to solve the wrong (or nonexistant) problems.

And there is nothing wrong with adding do-dads to your car just because you want them. It's your car, do what you want. (Yes, I know it's not literally _your_ car...) I just like people to be making informed decisions and not burning time, money, and effort needlessly - and often, multiple times...

@ Art

Not a problem at all, it's actually reassuring to know that a real professional engineer is here to verify and check what are my assumptions. I will talk with my prof tomorrow to verify how and at what location he is getting these temp readings from.

All 914er question:

In the vain of reinforcing that an Autocross run shouldn't get a 914 oil temp high:
When I was running slolams (that's what we called them here in CA) a usual run was 40 to 60 seconds. So I am wondering if some you you AutoCrossers simply REMOVE the cooling fanbelt for such a short run and pick up a handful of HP. There is usually plenty cool-down time between runs and the battery will last all day.

I know that Formula-V's haven't run cooling fans for DECADES, so what say you guys?

Terry

I say -- the fan's bolted to the crankshaft. If you want to suppress the alternator drag, easier to open the field wire.

When we ran quallcomm in July at the Parade ( 90F ambient ) on a 1:20 long course we didn't have temp problems with our electric fans. We were running the same motor as now ( ~180hp ).

edit: we do have a fanless oil cooler stuck to the firewall above the engine though.

Artechnika:

I had to smile and my mistake! I haven't worked on ar 411 motor in 30 years and FORGOT that the fan is bolted to the crank, rather than belt driven like my old
College car: a hand-me-down '56 Karmann-Ghia, after big brother got his degree!

For the last 6 years, I've been working on my southern NASCAR Accent since "I Got ME Some Chivy!" and working on my chevy 383 smallblock in my 914.

Bottom line: I was trying to make a point that for a 1 minute run, the 411 engine should NOT get hot.

Thanks for re-directing to the path of Purity,
Terry

Out of curiousity, would/could you provide some rough dimensions for your front bumper/valence slits (ie. size and shape), as well as any reference points they are located from (ie. from the ground, front trunk floor, etc.). Also, was that air dam custom built or was it a part that ordered from a catalogue (ie. Patrick Motorsports)?


Hi Backdraft,

In spite of the fact that you gave me NOTHING , I’m happy to share all the amazing technology of the front-end of my car: (just pulling your chain)

-First off, you can see that I have the hood removed as I finish my transition from bottom to top exhausting.
-The nose-piece is a standard product from Rennsport.com, Monrovia, CA, but they appear to be out of business.
-The splitter I made myself from 12” thick honeycomb stock and formed the leading edge with Bondo. It is 67” wide encompassing the nose piece and the outboard channels, sits 9” from the deck and extends 5.5” forward from the nose piece.
- The Standard nose piece has a center opening for an oil cooler with 2 side openings for brake ducts. However, for my applicaton, I channeled all of the openings for radiator cooling for my Chevy. The openings measure 5.75” X 20.5” in the center with 2 other openings of 5.75” X 4.25”.
-Outboard of the radiator intake, I created my own front brake cooling ducts with an opening in the nose piece of 4” X 9” which feed to 5” ducts to the brakes.
-At each outboard side I created a 3.25” wide air channel with an acceleration ramp. The first intent was to create an integrated air control system between the splitter and the fender flairs, also from Rennspeed. While I was at it I added the airflow acceleration ramps as per common practice over the last 35 years.
-All work was carefully based on the time-tested Engineering Principle of “That Looks About Right.” Please refer to Mark Donohue’s “The Unfair Advantage”: “If it looks right, It’s Right!”

@stew

Lol, as they say, you gotta give something up to get something back. Anyways, thanks much for the in-depth info, I'll try to model it as best as I can and get back to you with any findings.

If anyone else has any intriguing airflow modifications they've done or seen, feel free to let me know. I'm trying to gather as much data as possible on the variations of 914 aero designs out there and come up with some scientific/experimental evidence (or counter-evidence) behind these modifications.

Btw, just to clear things up a bit, this undertaking is not specifically just to look at the validity of certain modifications for my univ sponser's autoX vehicle, but to look at the wide array and range of aerodynamic modifications for the 914 that have popped up over the past 20-30 years and perform some experimental and flow analysis on them.

My apologies if someone already post this. But you may find this old classic interesting. I know it's more about overall body aerodynamics. But since we still might argue about what your car really needs and want to talk about studies, perhaps you'll get something out of it.

http://www.cassidy-online.com/porsche914/a...aids/index.html

Hi Backdraft,
I would be VERY interested in what your modeling software shows about the nose of my car. Do you think I've GREATLY improved the front aero?....Ya' know something just a bit better than a BRICK?

Terry

You have more downforce than a brick, lol.

WRG to tufting the rear deck, I ran a test with tufts of yarn on & behind the engine lid 5 years ago. Here's a pic showing how they were laid down after coming off the track. I also ran a video camera aimed through the rear window. I have that video stashed somewhere.

Click to view attachment

Thanks, I know about that, because that's the exact same professor that's I'm working on this project for.

Hi Backdraft,

While I was waiting for your aero analysis of the front of our 914s, I just HAD to make changes: As I posted earlier, I am now exhausting the radiator out the top of the hood.

I'd love to see what you think I've done to the Cd now!

Whaddya' think the new flow out to top of the hood does to the car?

Best,
Terry

When tonyakavw went through trying to cool a suby with the rad in the engine bay I think the cassady stuff was linked to. If you have time look at a fiero and the way it's rad air flow is. Also a mr2 might be a good place to look.

I would do a base on the car to know what is really what so all your work is not in vain. Ambient air same track and all. He probably won't do it but the hole in the hood is the easiest way to make this work the best. Try that first on your model.

For just a quick look find a 916/914 and look at the front bumper.

Hey Backdraft:

Long time no HEAR! I was hoping after we guys offered up the multiple front-end configurations, you would come back with AMAZING analysis and information. Come-on, now, Schools over for the year.....Give it UP!!

Then there is another issue for you to check-out on your sophisticated software: I have cleaned up (aerodynamically) and "prettied up" the radiator exhaust on the hood of my car. Take a look and let me know if this has improved my Cd and what coeficient value would fit my car.