Rear Diffuser [Merged 4-9]

[EclipseTrbo420A]

You guys first need to decide whether you want to do this for the look, or for the downforce.

Building one for the first reason is easy, the second reason is much much tougher.

I have a good design for the 2nd...I just need some large sheets of Black ABS plastic ....anyideas on where to get that ?

 

[leet]

Keep in mind that for a diffuser to work properly it is going to have to start before the rear axles. The entire underbody of the car will need to be flat and feed into it.

I've looked into doing and and and came to the conclusion that any gains to be had are simply not worth the budget it would take to do it correctly.

An easy way to gain some downforce is to make a tray for the front end. I fashioned one and the improvement in high speed stability was notable, however, it didn't react kindly to road debris.

 

[neilb]

^^^ what he said.

If for looks (and basic aero smoothing), just build something into a hacked up rear bumper . The underside is so lumpy that I doubt it'd do much.

I know what you mean about some aftermarket stuff though, they could be used as chutes on drag cars.

If for real use (downforce), i wouldn't bother if it's for your roadcar. The proximity you need to have the car to the ground to get anything usable would be almost undriveable on regular roads. Not to mention, under body panels to smooth air flow, side skirts to reduce air leaking in from the sides, gettting rid of engine bay heat etc.

 

[leet]

Engine bay heat is an easy solution, you just have to build a few small intakes into your bottom front panel and then install a LP inducing vent in your hood. You could also fashion ducts to direct airflow to your brakes if needed.

 

[JOEY A]

You guys first need to decide whether you want to do this for the look, or for the downforce.

Building one for the first reason is easy, the second reason is much much tougher.

Yeah im geussing he wants to go Wagon racing or when hes doing a touge run to feel like a race car driver...

 

[mavisky]

Yeah im geussing he wants to go Wagon racing or when hes doing a touge run to feel like a race car driver...

Maybe I should've had a rear diffuser on my Red Rider when I was racing down those hills at 5 years old. Probably would've saved me from a couple of those horrific accidents.

 

[FORMONTOYA]

Yea, I imagine he just wants to build/buy something that will eliminate the tendency for the rushing air at speed wanting to blow the rear facia off the back of his car...just a misuse of terminology.

 

[Splitpi]

Nice work, but may I suggest a way to fasten it so that the bolts are "hidden". Though it would require extra work.

1) Make a fiberglass liner that fits on the inside of the lower bumper lip. It would look like a giant U as it follows the bumpers profile from the inside of the bumpers lip.

2) At each location where you want to bolt it, drill the hole through the bumper lip and the fiber glass liner.

3) Epoxy the bolt nut to the fiberglass liner.

4) Mount the fiberglass liner in its proper location on the inside of the lower bumper lip.

5) Mount the diffuser as shown in the second photo. And using your bolts, bolt the diffuser through the bottom lip and into the fiberglass liner where the nuts will hold bolt.

This approach will releave the stress and strengthen the lower lip of the bumper and hopefully alleviate tearouts. Thus the only thing shown would be a low profile bolt head. And even these could be countersunk slightly. A cheaper, easier approach would be to simply epoxy nuts to the underside of the lower lip of the bumper. But I think there are benefits of doing it the way I suggested.

Anyways, it looks great... and goodwork on it.

 

[STECARS]

I seen this diffuser in the classifieds for sale a few months ago !

 

[No Mo STi]

I'm not one for changing the body style of these cars in any way but I've always enjoyed two things, a carbon fiber hood and a bumper diffuser. My question is, why is it that I never see any of these on DSM's. Are they useful or just a waste of time and money? Will it actually do as it says? Has anyone put them on a 1g? Would there be any reason for me to cut apart a perfectly good bumper? I've included an eBay pic also (not the one's I'd buy). Also, does anyone make a rear diffuser for 1g's? I saw a thread for 2g's, but nothing for 1g. Any help is much appreciated!!





http://cgi.ebay.com/ebaymotors/GOLD...16232QQrdZ1QQsspagenameZWDVW#ebayphotohosting

 

[king_of_HTX]

By diffuser I thought you meant the panel underneath the rear. I'm sure the one you posted is pretty much universal and i'm also quite sure it would reduce the drag being caught by the rear bumper a little also. I've never seen it on any dsm's but it can't look too bad.

 

[TwoLiterLaser]

I think it would look sweet.

But really would be the point other than for looks? I can understand getting a rear diffuser if you have a completely flat underside. But to just get a rear diffuser would really have little noticeable affect. I think it would be better to get a front lip that generates down force and possibly a wing that generates down force, then look into a rear diffuser. Just my .02

 

[inneedof]

jm fabrication makes one for 1gs

http://www.jmfabrications.com/catal...id=88&osCsid=1d4906a83ebc0c527d40713147fd3378

 

[red_devil]

How are they a diffuser? they look nothing like what you find on a car that has a real diffuser and must be completly useless. They are meant to channel air up behind the bumper to create down force, these are just gaping holes in the back bumper to let trapped air escape.

 

[jtmcinder]

And without some real data, I'll continue to wonder if putting holes in the rear bumper is worse than leaving it stock. The key to a diffuser is allowing the high-speed air beneath the car to slow down smoothly, preferably as far back as possible. By allowing air to go through the bumper, the slowing could occur just behind the gas tank, instead, which is sub-optimal to say the least.

Go find a Lotus Elise and stare at it for a while. That diffuser was tweaked in a wind-tunnel for months, if not years.

- Jtoby

 

[No Mo STi]

I would love to do both (rear diffuser and bumper diffusers). The bumper diffuser is used to release built up drag under the trunk and the diffuser will also smooth out the air flow under the car. I'm glad to see that someone has made a rear diffuser. Thanks everyone for the help.

 

[inneedof]

at high trap speeds i think they might be pretty helpful, i would think you wouldn't see much improvement on a 12-13 second car.

 

[TwoLiterLaser]

With a drag car I don't think you would want to produce down force. Shep's car hits 195 mph and he don't need no stinkin' down force to keep it kinda straight.

 

[roadrunner2176]

You almost never see those brackets on a dsm because the rear bumper support is in the way. After you remove that, and cut your holes out, your looking through the bumper right at the rear hatch area. They would have to be installed lower; these bumpers flow forward so the lower they get the tighter the hole becomes. Not worth the hassle in my book. Ended up making my own, excuse the crappy picture.

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[No Mo STi]

I'm not trying to produce downforce. I'm trying to reduce drag. To me if you do a combo of the under tray and the "tail holes" would do this. The rear diffuser would catch and smooth out any air flow up under the gas tank and the bumper diffusers would release any air that gets above the rear diffuser. Am I looking at this logically...I'm gonna try to draw up a picture so someone can confirm it for me.

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hopefully this is understandable. I have the artistic skill of a child in dipers!

 

[jrpmp69]

Would a diffuser make a difference on a 2g since the rear bumper acts as a scoop for air?

 

[jtmcinder]

Making the bottom of the car flat and smooth is a completely different issue from diffusers. Please feel free to start a new thread.

- Jtoby

 

[Boo5t_Addict]

Absolutely pointless. Unless you plan on going 195 mph like Shep, you're not going to notice any differences at all from these types of mods, because the underbody of your car in itself creates too much turbulence. Rear diffusers on, say, Formula 1 cars not only undergo years of wind tunnel testing, but also have the entire underside of the body trayed up, and have venturis built in. If you want to waste the $$, then by all means, go for it.

 

[No Mo STi]

Making the bottom of the car flat and smooth is a completely different issue from diffusers. Please feel free to start a new thread.

- Jtoby

What is the difference? Is my drawing a inaccurate misrepresentation of how air flows? To me, I think that's is how it should work but I'm in the dark b/c I never took a physics class and like I said...I'm not an aerodynamisis. Please feel free to explain how it works b/c I'm just throwing up ideas that I don't see anyone else trying. You had said in an earlier post that the main purpose of a rear diffuser is to create downforce. How would it create downforce if most of the air is flow on the underside? Wouldn't this create an up pressure/lift?

 

[Iroc_g]

I looked into getting these made for 2g's. My interest was purely cosmetic, but i wanted to design them to be functional for those that thought they needed that.
I got a local guy who does carbon fiber to agree to make 10 of them, using my car as the template. However, the costs of doing this were do high, getting 10 people to but money down would have been impossible.

And honestly, id rather buy a 3065 instead of a bumper cover for the same money.