2G Rear Diffuser Design

[snowborder714]

I would advise not using those plastic screw clips. They suck and fall out fairly easily, or are just a real pain to remove without having access to the back side.

I'm really not quite sure what I'm actually looking at, but the CAD drawing looks like a nice design.

How much in the way is the bottom of the spare well? Just a bit, or would it require somewhat significant modification?

 

[Atuca]

This is also a hurdly I am having to overcome. I think a "BFH" and removing the rubber seal will solve this problem, but these two things are the last thing in the way of this diffuser and the mounting flush against the bumper cover. I took a picture of one (at an angle to prove the mounting panel was currently installed) and you can see it mounts flush from the bottom of the bumper, to the bottom of the trunk, to the mounting panel I made. The angle the shot was taken (about 7-8* + jack stand angle ) The only thing in the way are as pictured. You guys agree a BFHammer to that and no need for a race version now?

The only part of the trunk that is in the way now with the way I have the newest sub frame panel mounted, is the rubber gormet and the little lip around the gormet. I think if you just "persuade" that bit up a little bit, and out of the way, we will be good. I am just assuming my math is off with 1/4 of an inch changing the angle so much, but if I hit within 1* of 7* of which I calculated, I am happy with that.

The picture was taken as level as I could with my phone to show that from the bumper straight to the mounting panel, the only thing obstructing it is the "thing"/rubber gormet as seen in the photo. I took a second photo (previously) that shows the two gormets as viewed from afar.

Does that clear it up?

The picture of the diffuser design does look to be a little dark on my work computer, I'll see if I can set up some better photos. I can design in Blender, not very good with light composition The 4 inches that sticks out the back starts from inside the muffler hole mirriored to the passenger side of the car. The outer fin starts at the outside of the muffler hole and lines up with the inside of the tire, to keep the turbulance from it from inturpting the flow of the center channels of air under the car.

If the plastic clips won't work, you have any suggestions on what will? Does the diffuser need to be structural to work, or just be able to stay in place and just be sturdy?

 

[snowborder714]

I don't think it needs to be integrated into frame rails and such, but needs to be as solidly mounted as possible.

 

[greengoblin]

It need to be able to handle firm hand pressure on it in any area without bending or flexing.

You also would want it mounted well enough that a small road hazard would not rip the darn thing off. Plastic clips are a no go.

Kevin

 

[H@xtGSX]

Sheet rock anchors... The ones you drill a hole for, stick that spring loaded anchor into that opens up inside to grip the panel, and has the bolt sticking out through the hole. Use a washer and lock nut on each anchor to hold the diffuser in place. That won't pull loose unless you rip the bottom of the bumper off too.

 

[eclipsegsx1736]

Very cool! Looks good from what I can make out so far. From an aero standpoint, I'd think the bottom of the strake should be parallel with the ground, which appears to be how you designed it. Not sure how critical the angle of the end of the strake is in relation to the ground, but making it perpendicular to the ground seems like the best idea. If it was perpendicular to the diffuser deck, the bottom edge of the strakes would stick out and would be a great way to cut someone's shin open!

How far forward does the foward-most part of the diffuser deck reach, in relation to the axle centreline? For some reason the strake height seems really shallow to me at the back of the car, but maybe I just don't realise how little distance we have from the rear axle centreline to 4" behind the back bumper for a ~7* rake. I love the diffuser designs with strakes that pull air from around the front of the rear wheel and direct it inward toward the centre of the diffuser, but I don't think this could be made legal for our rules restrictions. This is what I'm describing, although this extreme of a design is certainly not legal:

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[ed1380]

Dzus clips should be strong enough. That's what we use on the fsae cars

 

[Atuca]

Very cool! Looks good from what I can make out so far. From an aero standpoint, I'd think the bottom of the strake should be parallel with the ground, which appears to be how you designed it. Not sure how critical the angle of the end of the strake is in relation to the ground, but making it perpendicular to the ground seems like the best idea. If it was perpendicular to the diffuser deck, the bottom edge of the strakes would stick out and would be a great way to cut someone's shin open!

How far forward does the foward-most part of the diffuser deck reach, in relation to the axle centreline? For some reason the strake height seems really shallow to me at the back of the car, but maybe I just don't realise how little distance we have from the rear axle centreline to 4" behind the back bumper for a ~7* rake. I love the diffuser designs with strakes that pull air from around the front of the rear wheel and direct it inward toward the centre of the diffuser, but I don't think this could be made legal for our rules restrictions. This is what I'm describing, although this extreme of a design is certainly not legal:

Everything you stated is true. Since all you see is the diffuser panel at a flat angle in the render, the fins are the ones showing the angle of ~7*. ATM, I plan on having the fin ends perpindicular to the ground, which would mean they are flush with the back of the car. No scraped shins here in design.

The panel mounting location is maybe 3 or 4 inches from the axel. The subframe mounting solution I devised before had it a bit closer to the axel but that was part of the reason the trunk floor was in the way. If I make another "race" version it may be closer to the axel since we could remedy the trunk issue with a sawzall.. but at the same time a complete under tray would/could be incorporated so it would matter little where the mounting point is at that time.

I just have completely straight fins at this point in time. I think I hit all the main points of keeping air from the wheels away from the rest of the diffuser, and having fins long as possible.

I'm guessing everything is looking good so far though? Replies such as "Looks good" is good enough for me if you are viewing the thread and just want to show support for the style. It may take a photo of the plug mocked up on my car before the 4" of diffuser stricking past the bumper can be visualized for some maybe. I tried to get a good angle to photoshop the model, but I am not that good...

 

[turbosax2]

If you're set on getting a specific angle on it, how can it NOT be adjustable? This will change based on the rake of the car, no?

 

[greengoblin]

If you're set on getting a specific angle on it, how can it NOT be adjustable? This will change based on the rake of the car, no?

It would be ideal to have it be adjustable. That being said most people don't run rake. Atleast not many I have seen.

 

[Atuca]

You are correct Eric, it needs to be adjustable.

Without modifying the stock bumper mounting points, you cannot cut the bumper up higher. Without causing drag, the front mounting panel cannot get any lower. With those two extremeties as set facts, I am barely able to achieve that 7* I am after WITHOUT hitting against the trunk floor.

Because of all the restrictions I just named, that is why I figure I am going to have to make a "race" version that resolves those issues to get a desired angle outside of the "stock" setting I would be shipping these at for the street version. This "street" version will have to remain as close to a stock bolt on option as possible. Cutting the trunk and creating a custom bumper mounting solution for adjustable diffuser angle would be requirements for an adjustable "race" version.

The front mounting panel is in a pretty damn perfect placement. I don't think I could move it around much more in any beneficial manner after a month (~10 full 10+ hour weekend days) of messing with it. I think I will cast a mold of this third one and use the same panel for both this version, and any future "race" version.

 

[ViciousLord]

I would love this piece! But I removed the trunk... I have a flat panel welded in.

 

[Atuca]

I think you'll be just fine. Since I need to create an adjustable mounting solution for a race version, perhaps you be a good candidate for assisting in the creation of it.

ATM I am thinking of creating a type of L brackets that mount on the top of the diffuser, and then butt up against another set of L brackets that are mounted on the frame rail (where the two bolts that hold the crash beam connect) aimed down. Cut some slits into the center of the brackets and using a few bolt and lock nuts, bam, adjustable. I'll have to create a way to have the L brackets swivel at the corner (can't always be a set angle if the angle changes with height adjustment.. but I digress...)

I'll cross that bridge when I get there though, but again, to even take advantage of an adjustable diffuser, aside from cutting the trunk out, you'll have to cut your bumper cover and then doing that means creating another lower bumper cover mount as cutting the trunk removes that lower mounting location. Wouldn't want to cut the bumper cover and have it flapping in the wind after all this work creating a firmly mounted diffuser right?

 

[AngelOfPassion]

Wow, this is looking really great.

Also, how difficult do you think mounting it will be with a 3" exhaust? I think you said there would be some cutting involved earlier. Is this still the case with the current design?

 

[IrishBeatdown]

Well if you ever need to demo test anything let me know
Depending on how friendly the staff is at college, I can 3d print/machine stuff at cost.

You have access to a 3d printer? I am freaking jealous. I love that technology. When I first saw video of 3d printing, my eyes basically bugged out of my head. Most intriguing tech ive seen to come out in the last 10 years, the possibilities are endless.

 

[ed1380]

You have access to a 3d printer? I am freaking jealous. I love that technology. When I first saw video of 3d printing, my eyes basically bugged out of my head. Most intriguing tech ive seen to come out in the last 10 years, the possibilities are endless.

There's one at college. Also a machine shop. I better be getting something back with the money I spend.

 

[Atuca]

Wow, this is looking really great.

Also, how difficult do you think mounting it will be with a 3" exhaust? I think you said there would be some cutting involved earlier. Is this still the case with the current design?

Yes. Any one of you DSMers can look under the rear of your car and see the lowest hanging part of the car would probably be your aftermarket exhaust, followed closely by your rear dif. In order to keep this thing from becoming drag (keeping in mind one of the main goals of this design is to remove the drag from the bumper parachute) the lowest I wanted to set the difuser was just above the gas tank and floor panels of the car. If you look at the picture I have of my front panel plug, you can see that the rear sway bar and how it ramps up and over where the stock exhaust would be. Imagine that your aftermarket exhaust would likely enter past the sub frame near that location, and then follow w/e path directly from there to the stock bumper cover outlet location.

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I think for most stock location aftermarket exhausts, people will have to cut the diffuser into two pieces. As Beau stated, if someone wants to cut up the aero diffuser instead of routing their exhaust more efficiently, they can choose to do that. I'm sure in time if my diffuser proves itself as a drag reducing down force producing piece, rerouting the last ~3 feet of exhaust piping and your muffler to exit the car higher then the stock location may not be too farfetched an idea.

Its hard for me to answer that question, and again, was part of what took me so long to design the diffuser. I'd love to just have a lower hanging bulge that would work with all exhaust setups, but that just wasn't the best aerodynamic design. I tried to think of how I'd do it, but there wasn't a one size fits all.

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If you look at the different ways the exhaust can exit out the back, It can shoot straight from the center of the car, to the bumper exit. Sometimes it cuts nearly 90 degrees twards the driver side, then 90 degrees straight again to come out the bumper exit straight. I think the stock GST (even some aftermarket) exhaust goes OVER the rear sub frame and in that case needs no hole cut at all in the mounting panel or maybe nearly half of the diffuser panel. There just too many different ways the exhuast can exit; I'd basicly have to box off the entire driver side of the diffuser lower causing drag for that entire 1/3 side of the car. I might then have to mirrior that over for asethetic reason, or maybe even to keep drag even on both side of the car? After all was said and done the flat downforce producing part of the piece would be very small. And for anyone who's exhaust doesn't inturpt the diffuser panel, a bulg would just be non functional (negatively affecting the purpose of the piece even) and unwanted.

Long story short (maybe you just wanted a short answer to begin with ), there may be cutting needed anywhere your exhaust is the lowest hanging part of your vehicle.

 

[snowborder714]

Stock routed GST exhaust (2.5" exhaust piping).

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[ViciousLord]

If I get this piece i'll be routing my exhaust to work with this. I want full function!

 

[kamikazeredneck]

I don't know if this would work but for those of us that are cutting up the spare tire well and bumper, you could move (with modification of course) the diffuser up in that area and then you could probably still get the functionality of the diffuser and still have the looks of your aftermarket exhaust. Although it really is the easiest option to just cut the exhaust off short run a turndown but that is subject to opinion.

Now something that I don't know if it has been brought up but for those people that still want to drive their car on the street, you have to have the exhaust exit behind the rear axle on any vehicle but pick-up trucks. I am pretty sure that is for all states but one should check this out in their area before they just start cutting up their exhaust. I know I got a ticket with this on another one of my vehicles and just thought I would let people know.

 

[Scott McIntyre]

These photos make me wonder if it'd be possible to cut out the spare tire well and have the exhaust exit out through the middle of the rear bumper, above the diffuser.

Kinda like...

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[H@xtGSX]

Of course you could....You could route it out the roof with stacks if you wanted to, with enough cutting and welding. I would just cut the spare well off, route the pipe to mid line, and have exiting just below the license plate. Then just fit a plate over it and weld the spare well hole shut. It would be easier with a small fuel cell (10 gal) and have the factory gas tank removed also... Save some weight, free up space.

 

[ed1380]

Do racing organizations require a muffler? In a dedicated track car I would just run it out the front bumper.

 

[snowborder714]

Most rule books require it to dump behind the driver, but it will all depend on what club you want to run in and what class you want to compete/be grouped in.

If it was me, I'd just have it turn down or out a side behind the driver (before the gas tank in the FWD - see picture above) which would keep it out of the way of the diffuser and not require you to reroute it and hack up the bumper.

 

[H@xtGSX]

Dualies out the sides in front of the rear wheels like an old Corvette. That is exactly what I was planning on doing until I saw the clearance the 3" pipe would have crossing the rear drive shaft. A single out the drivers side can be done easy enough, and I did it for a short time, but it is loud as hell and the exhaust is in your face every time you open the window... And if you're running catless with a big pipe and lots of fuel, that means your eyes will be watering at every stop. I know this from experience... That is why I have the big Magnaflow out the rear now.

I would say keep it mid line, dump it before the rear axle toward the pavement, and let the gases get directed back and out by the diffuser.