2G Rear Diffuser Design

[JonathanNL]

At this point though, I am officially calling the AWD rear subframe mounting panel "DONE"!

Looks good, but... where's the FWD love?

 

[greengoblin]

Looks good, but... where's the FWD love?

I'm pretty sure the bottom pic is the FWD unit.

 

[snowborder714]

If you're referring to the bottom pic in post #96, that's just the other face of the part. He hasn't done a FWD unit yet as he doesn't have a FWD crossmember to build off of.

 

[Atuca]

Unfortunately, Brian is correct. However, I do intend on creating a fwd sub frame mounting panel soon as I have access to one (and once the diffuser panel is done), which will work with gst, gs, and rs models.

 

[Dyesuperman]

Can't wait to see this finished. Keep up the good work!

 

[Atuca]

Ok diffuser panel is just about done!

Just needs to have the counter sink for the strake mounting location done, and I bit the bullet and bought a router and some bits. I bought it at Harbor Freight for like 30 (maybe 40) bucks. It probably is complete shit, but if it can last long enough to do these few cuts, I guess w/e. I can say that I've spent 100s upon hundreds, dare I say nearing 1000 dollars, doing this project, I got the receipts to prove it. Granted I did have to buy just about every tool from start to finish on this project. I mean.. I didn't even own a drill

As it all comes together though, it's all worth it. This weekend was exactly what I needed, I was excited as much as I was the first day i started the project. This weekend, I got to nearly complete the diffuser panel. There's not much to say really. It cleared the wheel well area, clears the sway bar, and after counter sinking the trunk floor "things", nearly fit the bumper perfect just as measured.

There is an apparent "line" on the bottom of the bumper. I had originally tried to follow that line to use as a permiter of the diffuser, but there were several areas that were much thinner then other areas of the bumper (in reguard to mounting locations). I ditched the idea and made my own line by eye balling it to give a uniform curve to the diffuser. Making sure I was symetrical was quite difficult, but after measuring over and over and over, I think I am good enough no one would call me on it. And if someone did.. well.. tough!

I looked at different thickness of metals with a 5 inch portion (the largest a strake can be according to NASA/SCCA rules) and 90* angle. Well.. I am going with 1/16". Any thinner it was easy to bend the metal and I just couldn't stand the thought of the strakes waving around in the wind, so 1/16 it is. It will be counter sunk into the diffuser with (at the moment) planned 3/4" mounting base. I didn' tlike the idea of large slits cut into the diffuser. The strakes run the length of the diffuser amd I think 6 large cuts in the diffuser base would severly weaken it. By counter sinking, the diffuser thickness and integrity is kept in tack, while the strakes are still flush with the base of the diffuser.

Unless someone has a really good arguement to make by next week, that's the route I am going to take.

Here's the pictures, next week is strakes!

BTW, the picture of it on the car was before about 5 hours of shaping and resizing. It tucks under a bit better then seen here, but I am showing this picture anyways because it shows the logic behind the 4-5 inches it sticks out past the bumper in the center. I'll redo another render with the new measurements I have now. I also will try to give the diffuser a slight bend to help it mount better at the back of the bumper. Perfectly flat if leaves a bit of a gap I don't like, so I will try to remedy that before I mold it.

 

[H@xtGSX]

Are you thinking of molding back from the bumper to the top of the rear lip? I know the protrusion is necessary, I just don't know if leaving a sharp pocket on the top is going to affect anything...

You are picking up tools the way I started many years ago... Needed them to finish projects that required stuff I didn't have. I have a whole bunch of strange tools now. The nice thing is that investing in tools is something you don't have to regret, because you will be using them again and again.

 

[Atuca]

No, I don't think there will be anything on top of the diffuser there. I've seen several diffuser that have a lip, or in some other way extend beyond the bumper. None of those ones had anything, so I had made no plans to add anything. Once the strakes are installed, it will look a little less "odd" just having the diffuser stick out, the strakes on the ends will box it in and make it look like every other diffuser out there, just.. DSM style

 

[Atuca]

LOOKING FOR TESTERS!

As one of the final steps to this design project, I need to find a few people who would be willing to test the Street Version out. I have received several PMs but I would like to ask a few things from those who may be interested.

I will be looking for 5 individuals with a 2g GSX/TSI AWD, who feel they can provide constructive written feedback, and pre/during/post installation pictures of the rear diffuser and mounting panel ranging from design, presentation, function, and craftsmanship.



If interested, Private Message me the following:

1) Years you've owned a DSM.

2) Experience doing "DIY" projects/installation (self evaluated on a 1-5 scale, perhaps tell me what you did? Turbo installs, suspension, ect. w/e you consider DIY)

3) Your car's purpose (competitive racing [what's your experience?]/street use)

4) A short description of why you want to test this, and how you are going to test this. Do you have any intention to reroute your stock route exhaust for this?

5) An email address you check daily



I will be picking a variety of people ranging from different aspects of the questions above so that I can get the largest range of feedback from different areas of expertise, so if you are a self proclaimed n00b, I still need to hear from at least one of you Answer's don't have to be super long, just enough to get the point across. Be aware that you may require several tools/bolts/ect for installation. More on that via PM.

This will not be free handout; More on this via PM. You will be keeping the diffuser after you are done testing. Fiberglass or carbon fiber construction to be discussed in PM as well. Honestly, ANY question pertaining to the testing of this, please Private Message me. This thread needs to remain unlocked and available for reporting design concerns, so keep the info posted here related to that.

If you have a question about the design you want answered before committing to be a tester, feel free to ask that here. I may make one post with all the design highlights just to help declutter the 4 pages of this this thread a bit if needed, but all the info is here. The only difference from what you've see here is the product you'd receive (if chosen), will be that it's made of fiberglass or carbon fiber. I want to place one large order for materials hense the reason I do not already have a fiberglass version to share already. This will greatly reduce the cost for me (and in the end you) to do it in bulk like this with high quality materials.

I expect this feedback to potentially help with my design, but more likely, to help with just the final presentation. If at the end I just am able to have a well documented installation guide to provide, then I will consider this a sucess. As this is my bolt on street version, and I have installed this on my car, I do not foresee any issues here (famous last words ) It will require the cutting the panel we've talked about to accomodate your stock routed exhaust (if you chose this), mounting holes drilled on panel and potentially your bumper, hardware to mount the diffuser to the vehicle, and hardware to mount the strakes. I will (and if needed, hopefully this thread) provide feedback to help assist through any process to get the diffuser installed.

Thanks ahead of time for anyone that responds, and sorry I can only choose 5. I fear still that the time frame to make even just one of these will be a while, and I want to keep it to just 5 so I can manage this clearly and precisely. I would expect to have these in your hands in at the latest 5 weeks from the time people are chosen. I'll be shipping these out 1 by 1 randomly as soon as they are constructed to start the feedback process asap.

I would like to pick the 5 testers from the PM submissions I get before Monday, November 12. Doing so means the last person should hopefully have theirs before X-mas still Try to get the info to me asap though to be considered, and I'll do my best to keep the time frame goals met.

 

[H@xtGSX]

One of the main pain in the ass things about panels like this is shipping, so take that into account. It won't be cheap, because of the odd shape and size. I made some carbon fiber fenders and they wound up running $28 a piece even though they weighed less than a large book. I take it as a given, but some people look at the price and are already stretched thin, then get hit with the shipping and throw a fit. My practice is to just factor it into the final price and never charge shipping. That prevents the "added expense" feeling some people get when they look at the price before shipping.

 

[Bud92gsx]

I just made a fromt one of these from sheet metal..Goes under front bumper.

 

[Atuca]

One of the main pain in the ass things about panels like this is shipping, so take that into account. It won't be cheap, because of the odd shape and size. I made some carbon fiber fenders and they wound up running $28 a piece even though they weighed less than a large book. I take it as a given, but some people look at the price and are already stretched thin, then get hit with the shipping and throw a fit. My practice is to just factor it into the final price and never charge shipping. That prevents the "added expense" feeling some people get when they look at the price before shipping.

Issues such as that are what I am hoping will be addressed with this test run. This will give me 5 different places to ship to to figure an average shipping cost. At this very moment, I havn't a clue.

 

[dradernh]

I just took fluid mechanics last semester... Isn't slower moving air at higher pressure, not lower? Isn't that how a front splitter works? I thought that caused a low speed, high pressure buildup on top of the splitter for down force.

I found to this thread via a search for unrelated info, but wanted to clear up a point here. I recently contracted with a well-known aerodynamicist to evaluate my race car, and one of the points he made was how a front splitter produces downforce. This is best shown in the below computational fluid dynamics-generated image of the front end of a car with a modest splitter extending forward of the front bumper. The area of low pressure is the blue area pointed to by the red arrow (see the scale on the left of the image for see what the pressures are in any particular area represented in the image).

The common notion that it's air on top of the splitter pushing down that produces downforce is in fact the opposite of what is taking place; it's air rushing under the leading edge of the splitter and into the low pressure zone residing there that is causing the splitter to pull the front end of the car down. In addition, you want the splitter's leading edge to have a rounded profile so that the air can easily wrap itself around that edge & rush into the low pressure zone at the highest speed possible, thereby maximizing available downforce.

BTW, the lines show the direction of air flow, and will disabuse anyone from thinking that a splitter actually "splits" the air forward of the car. The bow wave preceding the front of the car is forcing the air to take directions that may not be obvious.

Sorry if this is a hijack. It's just that this stuff is somewhat complicated & I wanted to share something I've learned.

You must be logged in to view this image or video.

 

[Atuca]

Other then the fact this is a "rear" diffuser thread, anything to do with the design of the diffuser is welcome Funny you joined DSMtuners just to make your point, but at least it was to contribute some useful information.

What would I need to provide to have a computational fluid dynamics-generated image of the diffuser I made and rear of the car. As I understand 2d images are much easier to produce then a 3d, but I do not currently have access to the tool. I do however have access to Blender, a 3d modeling program that I could use to made a rudimentary model of a 2G Eclipse and export hopefully to a support format for import in the fluid dynamics software.

This question goes out to the newest member dradernh, or anyone else who has access to one.

The idea just perked some interest in me

 

[eclipsegsx1736]

I found to this thread via a search for unrelated info, but wanted to clear up a point here. I recently contracted with a well-known aerodynamicist to evaluate my race car, and one of the points he made was how a front splitter produces downforce. This is best shown in the below computational fluid dynamics-generated image of the front end of a car with a modest splitter extending forward of the front bumper. The area of low pressure is the blue area pointed to by the red arrow (see the scale on the left of the image for see what the pressures are in any particular area represented in the image).

The common notion that it's air on top of the splitter pushing down that produces downforce is in fact the opposite of what is taking place; it's air rushing under the leading edge of the splitter and into the low pressure zone residing there that is causing the splitter to pull the front end of the car down. In addition, you want the splitter's leading edge to have a rounded profile so that the air can easily wrap itself around that edge & rush into the low pressure zone at the highest speed possible, thereby maximizing available downforce.

BTW, the lines show the direction of air flow, and will disabuse anyone from thinking that a splitter actually "splits" the air forward of the car. The bow wave preceding the front of the car is forcing the air to take directions that may not be obvious.

Sorry if this is a hijack. It's just that this stuff is somewhat complicated & I wanted to share something I've learned.

You must be logged in to view this image or video.

That's part of the story, yes, but the splitter also does cause a high pressure area above the splitter, which pushes down on the top of the splitter. In fact, you can see this happening in the picture you attached.

As far as diffuser testing, should we hold tight if we're more interested in testing the race version?

Beau

 

[Atuca]

Beau,

For you, probably yea? I can think of a few reason's an actual race car driver would want to wait for my race version. I'd have done it first since that's the version I personally would want to use, but the street version needed to be completed before I started hacking away at my bumper and trunk

The street version is anything but "just for looks", but it will be a fixed panel with no real adjustability from the calculated 7.8* angle. I honestly can't say how much more beneficial have the adjustability will be to someone, but the diffuser panel would be larger, have mounting hardware to adjust the angle, and well.. would just be a different product from the street version and cost more for potentially no gain.

As discussed/proposed, 95% of people will get the same benefit from the street version they'd get from the race version, as most vehicles' maximum diffuser angle can be no more then ~7* before the air seperates from the diffuser panel. I'm just a weirdo who's building a race car and would rather have the adjustability and larger diffuser panel and am willing to put the time into it, so I am

THAT SAID.... You can still test it though to help me collect factual data to prove (or disprove) the thing is more then just for looks. I've researched and designed it to be functional, but I would concede it is just for looks if data aquisition proves otherwise. That is part of what I mean by "presentation"; I am looking to gather information on what would be a truthful presentation of the product, and potentially figure out if I need to create a hardware kit or something for installation. My race version "open testing program" will be a much more indepth process then I plan for this, and those people I'll be lucky if I am not paying them by the time I'm done asking them questions and having them do stuff for me

And based off the amount of time its taking Kevin to finish his project, it may take me several months before I get around to making a race version and probably the end of the 2013 year before its ready for testing. So if you want something for the 2013 season... let me know

 

[dradernh]

What would I need to provide to have a computational fluid dynamics-generated image of the diffuser I made and rear of the car. As I understand 2d images are much easier to produce then a 3d, but I do not currently have access to the tool. I do however have access to Blender, a 3d modeling program that I could use to made a rudimentary model of a 2G Eclipse and export hopefully to a support format for import in the fluid dynamics software.

This question goes out to the newest member dradernh, or anyone else who has access to one.

The idea just perked some interest in me

I'm afraid I haven't the faintest idea. I'd start with Georgia Tech & see if I could interest them in looking at my problem. For free. Might be worth a try.

That's part of the story, yes, but the splitter also does cause a high pressure area above the splitter, which pushes down on the top of the splitter. In fact, you can see this happening in the picture you attached.

Actually, that is the story. Look at the air flow & ask yourself, how much work could possibly be being done on top of the splitter? You're stuck on the idea that the air hitting the front of the car (and the top of the splitter) is doing something of significance. With so little of it, with nowhere to go, and therefore with little speed associated with it, however, it isn't. Don't take my word for it, though - pick up a motorsports aerodynamics book & see what they've got to say.

Here's another example: A rear wing produces downforce not due to the air hitting it from above after coming down from the roof, but from the air that rushes into the low pressure zone along the lower surface of the wing. In action, it's the opposite of an airplane wing (because it is an airplane wing (sort of) - it's just that it's an upside-down airplane wing). The rear wing isn't pushed down, it's pulled down; any air hitting it from above (and there is some) is insignificant as a practical matter. This is why you want a rear wing mounted behind the rear deck lid (if you have one) - if it's over the deck lid, it's trying to lift the deck lid at the same time it's trying to push it down. Better that it's trying to lift the ground up to meet its lower side, since the ground can't move.

<End of Hijack> Thanks for listening.

 

[eclipsegsx1736]

Actually, that is the story. Look at the air flow & ask yourself, how much work could possibly be being done on top of the splitter? You're stuck on the idea that the air hitting the front of the car (and the top of the splitter) is doing something of significance. With so little of it, with nowhere to go, and therefore with little speed associated with it, however, it isn't. Don't take my word for it, though - pick up a motorsports aerodynamics book & see what they've got to say.

Here's another example: A rear wing produces downforce not due to the air hitting it from above after coming down from the roof, but from the air that rushes into the low pressure zone along the lower surface of the wing. In action, it's the opposite of an airplane wing (because it is an airplane wing (sort of) - it's just that it's an upside-down airplane wing). The rear wing isn't pushed down, it's pulled down; any air hitting it from above (and there is some) is insignificant as a practical matter. This is why you want a rear wing mounted behind the rear deck lid (if you have one) - if it's over the deck lid, it's trying to lift the deck lid at the same time it's trying to push it down. Better that it's trying to lift the ground up to meet its lower side, since the ground can't move.

<End of Hijack> Thanks for listening.

If this were true, then the length (depth?) of the splitter would not have an effect on downforce, but boy does it! Why? Because you're increasing the surface area that the high pressure air on top of the splitter can push down with. Of course, there's a point where extending the splitter does not produce additional downforce, as the high pressure zone at the nose of the car only extends out so far (dependent on speed and front nose design). I've been a subscriber to Racecar Engineering for a few years now and this was covered in an issue a while back while doing wind tunnel testing on a Mini Cooper racecar. I'll have to dig up the article and scan it.

Philip,

I'd definitely like one for the race car for next season! I'll keep up to date with this thread and see how the scheduling goes. If the "street" one is the only one that's available when the time comes, I'll go with that. I'd like to have one on the car early next year, so there's still time.

Beau

 

[Atuca]

In case it was misunderstood, I corrected my post that the race version probably wouldn't be ready til sometime end of next year, its just my guess. This one took plenty of time WITHOUT other car projects interfering. Wait a minute.. I thought you had a DD dsm anyways, you need a diffuser for both of them; 1 street and 1 race

We'll see about testers; push come to shove people always get more timid

 

[eclipsegsx1736]

In case it was misunderstood, I corrected my post that the race version probably wouldn't be ready til sometime end of next year, its just my guess. This one took plenty of time WITHOUT other car projects interfering. Wait a minute.. I thought you had a DD dsm anyways, you need a diffuser for both of them; 1 street and 1 race

We'll see about testers; push come to shove people always get more timid

Ah, well that's a little different then. I did in-fact read your post wrong. I'll shoot you a PM

 

[Atuca]

Still looking for more testers!

http://www.dsmtuners.com/forums/roa...075-rear-diffuser-design-4.html#post153128754

PM please!

 

[bettfootball]

You have a PM sir.

 

[Atuca]

Strakes are proto-typed!!!

I think these are ready to be mass produced already, I love them! What do you guys think? The "proto typer" even thought to maybe use a back plate? He had scrap metal and figured why not? I don't know if they would fit tbh as close as the trunk floor is now, but I like his thinking!

You can see now how the 5 inches over 3 feet strakes gives a nice long deep pocket of downforcy goodness! I hope my testers find this to be true!

Pictures!!!

 

[greengoblin]

Looking good. What is the the large flat section made out of ? Sorry if I missed it in a post.

 

[Atuca]

Thats just the plug (which was hard board). Test units and every units there after will be fiberglass or carbon fiber, depending on how much $$ you want to spend on materials.