Diffuser project

[The Stickman]

Ok I am starting on my difffuser and since I have the computer in the garage I thought I would do my best to supply live updates. This is going under my 1984 Oldsmobile Custom Cruiser wagon. So far I have only cut the passenger side outlets out but I think so far it looks mighty good. Here is the bumper I started with

https://static1.pt-content.com/images/pt/2011/02/001-1.jpg
Here it is after cutting out the outlets.
https://static1.pt-content.com/images/pt/2011/02/002-1.jpg

[Nessumsar]

I'm liking it so far! What material are you planning to use?

[The Stickman]

And now both sides done.
https://static1.pt-content.com/images/pt/2011/02/003-2.jpg
Now I will move onto the frame. I will be using aluminum angle. I think for the skin I will use sheet aluminum, but have considered fiberglass.

[The Stickman]

Ok starting to make some progress. Here are the vertical fences that I have started work on. Going to do another layer of fiberglass and that might be it.
https://static1.pt-content.com/images/pt/2011/03/0011-1.jpg

[musclecarmatt]

i'm diggin the wagon!

[The Stickman]

Ok got a bunch done today on the diffuser. I have one tunnel just about done. Need to add a bit of glass to the tops of the angles for just a tick more strength altough it feels pretty sturdy now. And I need to trim the rear to fit the contours of the rear bumper. I will be using Dzus fasteners to hold it on. This way I can remove it so it will be easier to tie down on the hauler. Anyway here are pics of the latest progress. Let me know what you think.
https://static1.pt-content.com/images/pt/2011/03/100_8164-1.jpg

https://static1.pt-content.com/images/pt/2011/03/100_8165-1.jpg

https://static1.pt-content.com/images/pt/2011/03/100_8166-1.jpg

https://static1.pt-content.com/images/pt/2011/03/100_8167-1.jpg

https://static1.pt-content.com/images/pt/2011/03/100_8168-1.jpg

https://static1.pt-content.com/images/pt/2011/03/100_8169-1.jpg

https://static1.pt-content.com/images/pt/2011/03/100_8170-1.jpg

[The Stickman]

Some new pics. Both tunnels are done. They will need some final trimming but for now I need to get them mounted and then I can start on the center section. This is going to look so trick when done.
https://static1.pt-content.com/images/pt/2011/03/100_8187-1.jpg

https://static1.pt-content.com/images/pt/2011/03/100_8188-1.jpg

https://static1.pt-content.com/images/pt/2011/03/100_8193-1.jpg

https://static1.pt-content.com/images/pt/2011/03/100_8191-1.jpg

[The Stickman]

Ok getting pretty close to completing the main part of the diffuser. I have both tunnels mounted with Dzus fastners and they are very solid. The center section is mounted with Dzus fastners as well. Hopefully tomorrow I can trim them and glass them together as one unit. I amd really liking the way this is coming out. Although I am not sure I can leave them that deep. Also I like hout they stick out past the bumper but that too might get trimmed back. Not sure yet. Ok let's get to the pics. The first if the spot where the license plate mounts. It is curved so that it doesn't match up with the plate. So we squared it off. Here you can see the difference from one side to the other.
https://static1.pt-content.com/images/pt/2011/03/100_8199-1.jpg
and here are both sides done.
https://static1.pt-content.com/images/pt/2011/03/100_8202-1.jpg
One tunnel solidly mounted. I had to mount the Dzus fasteners inside of the panel as I made the vertical fence too thick.
https://static1.pt-content.com/images/pt/2011/03/100_8203-1.jpg
Finally both tunnels, and center panel mounted.
https://static1.pt-content.com/images/pt/2011/03/100_8206-1.jpg

https://static1.pt-content.com/images/pt/2011/03/100_8208-1.jpg

[Bryce]

looking good.

[Motorcitydak]

keep in mind that these if done correctly will produce negative pressure at speed so they will try to pull down off the car. You need to be sure that your fasteners and the surrounding material can handle the load, figure around 100 pounds per each piece would be a high figure.

I am going to guess that your are building these more for looks rather than function. If you really want downforce at speeds then you need to start at the front and work your way back. All under hood air flow has to be controlled, under the car needs to be flat and smooth, front splitter to divert as much air around the car as possible, side skirts are a must to control air from leaking in or out from under the car and a decent rake helps too. The diffuser will help accelerate the air from under the car and works best with a spoiler mounted just above its opening which is not possible with your car. Another note is to route your exhaust into the very beginning of the diffuser, this speeds up the air which will create more downforce

[The Stickman]

keep in mind that these if done correctly will produce negative pressure at speed so they will try to pull down off the car. You need to be sure that your fasteners and the surrounding material can handle the load, figure around 100 pounds per each piece would be a high figure.

I am going to guess that your are building these more for looks rather than function. If you really want downforce at speeds then you need to start at the front and work your way back. All under hood air flow has to be controlled, under the car needs to be flat and smooth, front splitter to divert as much air around the car as possible, side skirts are a must to control air from leaking in or out from under the car and a decent rake helps too. The diffuser will help accelerate the air from under the car and works best with a spoiler mounted just above its opening which is not possible with your car. Another note is to route your exhaust into the very beginning of the diffuser, this speeds up the air which will create more downforce

Steve, not building them just for looks. More looking to clean up the underside air and get it out cleanly. The way my car is the fuel tank is very forward of the rear bumper. So the air is able to come across the tank then come back up and hit the one crossmember and get caught by the huge rear bumper. I figure this will be much cleaner for the air to exit Kinda hoping it doesn't produce downforce, although it sure looks like it could. Are you thinking it will produce downforce? It would be cool but not until I get the airdam done which might not be in time for RTTS. I do have a great idea for and airdam/splitter. I have been studying the aero articles in he advanced section and think I need test equipment before hacking a hood vent on my car but I bet one would help. All a matter of where.

[Motorcitydak]

If your fuel tank is in front of the diffuser then I would say that is a good thing because the bottom of a tank is usually quite smooth so that will aide in streamlining the underside of your car.

The entire purpose of a diffuser is to create downforce, its what they are designed to do. Im not sure if yours will produce a measurable amount tho, it will have to be relatively low to the ground to work. Also like I posted, it really helps if you have the other aero stuff in place. A front splitter and flat belly really help. The diffuser is supposed to speed up the air just before it leaves the underside of the car, this creates an area of negative pressure in the diffuser and thus downforce.

[SIK02SS]

Here's some good diffuser building read: http://www.frrax.com/rrforum/index.php?showtopic=5687&hl=diffuser

Rule of thumb to keep flow attached to a surface, is that the diverging angles need to be 15 degrees or less. You're going from a narrower in between the rear tires to the full width of the car after the tires (about 24" more), so they should get wider to maximize the downforce and minimize drag.

also, if you get tired of the glass: http://www.stillen.com/product.asp?id=STIFGTDIFF1&c=EX&year=&make=&model=

[Motorcitydak]

link to that frrax.com thread did not work for me

[The Stickman]

link to that frrax.com thread did not work for me

Yea me either. Those Stillen pieces are nice. Not sure they would fit and Not sure I wanna know the price.

[Bryce]

Those Stillen pieces are nice. Not sure they would fit and Not sure I wanna know the price.

http://www.stillen.com/product.asp?id=STIFGTDIFF1&c=EX&year=2005&make=FORD&model=GT

the price is $323.37

[SIK02SS]

link to that frrax.com thread did not work for me


Yea me either. Those Stillen pieces are nice. Not sure they would fit and Not sure I wanna know the price.

Sorry, maybe you have to be a member to view threads? don't know..

[Motorcitydak]

Those pieces are nice and thats a pretty good price for em. I just do not think they would work very well on any other car with that tiny opening. You want the outlet to be larger that then inlet but usually not by that much

[SIK02SS]

i think it's a 15* angle increase...i'm sure a google search will bring up a lot of good info. Biggest issue is a full on diffuser only starts working at ~90+ mph

[67blacklist]

... Biggest issue is a full on diffuser only starts working at ~90+ mph

well that's a problem that's fun to solve.....

[The Stickman]

OK I did some trimming and it is really starting to get there. There is about 6 inches of clearance from the bottom of the fences. While that is ok it I had left it hang out like it was it would have got smashed. I already drag my pipes at places and this was as far back and lower than them. So it has been adjusted and I think it looks better anyway. Have a look. Still lots of prettying up to do.
https://static1.pt-content.com/images/pt/2011/03/100_8218-1.jpg

https://static1.pt-content.com/images/pt/2011/03/100_8219-1.jpg

https://static1.pt-content.com/images/pt/2011/03/100_8221-1.jpg

https://static1.pt-content.com/images/pt/2011/03/100_8229-1.jpg

[Bryce]

nice work! I like the way it looks.

[RS_Customs]

It's looking good Neil!

Robert

[Motorcitydak]

What are you going to do about the areas you cut out on the outsides of the exhaust pipes?

Also if you can bend aluminum, which is not hard to do, you can bond aluminum sheet to rigid foam board which will be light and strong. I think ill be going that route instead of dealing with fiberglass

[The Stickman]

What are you going to do about the areas you cut out on the outsides of the exhaust pipes?

Also if you can bend aluminum, which is not hard to do, you can bond aluminum sheet to rigid foam board which will be light and strong. I think ill be going that route instead of dealing with fiberglass

The outer areas will get smaller tunnels. Problem is the exhaust pipes. The passenger side runs straight down the framerail. But the driver side if off a bit. I think because the fuel tank is offset more towards the driver side the guy doing the exhaust wanted some space between the 2. So I either find a way to get it right under the framerail, or make it exit right after the rear wheels, or do a custom center exhaust exit. But that requires moving the lic plate. And becuase of the window in the tailgate I am not sure If I could event recess the plate. So still working thru ideas.I love to work with aluminum. I never knew about bonding it to foam board. I would love to know more about that.

[sr73bu]

Nice Job Neil! It looks Great!

[Motorcitydak]

If you have to move the exhaust, you should consider what I wrote earlier. You can let the exhaust gas dump rite into the beginning of the diffuser, this will help by getting the airflow going and will suck more air into it from under the car. This is the rear diffuser setup of the 200mph SuperCuda

https://static1.pt-content.com/images/pt/2011/03/DSCF0683-1.jpg

https://static1.pt-content.com/images/pt/2011/03/DSCF0681-1.jpg

The aluminum thing is pretty easy if you can get everything right. You just have to make a few precision folds. If you get it rite you wont even have to try to weld anything

[v7guy]

for the fraxx.com link... you do have to sign up to view the thread, it's three pages of info though and a lot of it is from guys who run them for ORR.