: Rear diffuser options



Naf
03-19-09, 02:41 AM
Ok, we all know i have been on the search for a rear diffuser...

I found two options, VIS universal CF rear diffuser and another V1/V2 secret weapon...

I have attached pics of both...Roughly they will cost me somewhere between 700-1000$ before installation...I will SLICE my spare tire down to the min and install this wonder of the race world...

Say hello to more rear grip...

NormV
03-19-09, 05:28 AM
I think you purchased the wrong car...


Norm

Naf
03-19-09, 07:38 AM
Care to share why?

ctsv154
03-19-09, 08:08 AM
I too have thought about a rear diffuser but not one that gaudy. Something similar to these

http://i230.photobucket.com/albums/ee168/1LapSRT/RFR%20Pictures/RearDiffuser.jpg

http://img162.imageshack.us/img162/3854/venom100006047vr.jpg

ctsv154
03-19-09, 08:11 AM
No offense Naf, but the ones you picked out look ridiculous.

I still cant decide if I like the one on the SRT-4. I like the viper diffuser but I think the Neon might still be a bit much. Would have to see it on the ground. The thing is, I just dont think it would look right on our cars. Plus without the underbelly panels, I cant see a rear diffuser really doing much. It may help the turbulant air escape better but the whole point of the belly panels and diffuser are to keep the air clean.
http://img84.imageshack.us/img84/9071/ferrarienzoyn4.jpg

Naf
03-19-09, 08:39 AM
No offense Naf, but the ones you picked out look ridiculous.

I still cant decide if I like the one on the SRT-4. I like the viper diffuser but I think the Neon might still be a bit much. Would have to see it on the ground. The thing is, I just dont think it would look right on our cars. Plus without the underbelly panels, I cant see a rear diffuser really doing much. It may help the turbulant air escape better but the whole point of the belly panels and diffuser are to keep the air clean.
http://img84.imageshack.us/img84/9071/ferrarienzoyn4.jpg

You really dont know?

A rear diffuser is one of the best downforce enhancers with the least amount of drag...You can always slap on MASSIVE rear wing but you will have AMPLE drag on the car at high speeds and unneeded downforce at low speed...(though the rooster tail of rain water behind u is always a grin pleaser...)
The fins on the rear diffuser help direct the Vacuumed air in a straight line so you stay true and straight.

I like the one from the SRT but i see no angle where the vehicle causes a vacuum under the car? Normally you will see an elevation towards the rear of the diffuser.
To be honest the only one i really like is the VIS one...The other two are too much style then performance...

ctsv154
03-19-09, 08:46 AM
Okay Naf you're always right. Since you have suck deep pockets why dont you have one custom fabed to fit the car without looking ridiculous and tell us how it does. Seriously. I would like to see one that looks decent on a V.

SkullV
03-19-09, 09:13 AM
Naf...you should take a trip out to Tel Aviv today to show me your car...I know everyone here would love someone to get a first hand look at your work of art!

Although...i don't know if thats even an option in this part of the world these days...

Naf
03-19-09, 09:16 AM
Its such with an H not a k...

I have been lookin for someone to make me one, but like other stuff, i am stuck in a sandbox..No one likes doin business with international buyers...CC frawds, falsifyin no deliveries are just the tip of the iceberg i fight...

The VIS aught to be nice, there is another one, much nicer, but the pic wouldnt fit...its clean, but looks heavy...

I have a couple of subjects open with Specter and LPE. They are doin their best to keep me posted and happy...Big thanks to Matt from Specter and Kevin from LPE...

945liter
03-19-09, 09:26 AM
Go ahead make one of those fit.... at least the ones posted by the other members look like real diffusers and not off a civic body kit.

SkullV
03-19-09, 09:29 AM
Come show me your car!!!!

Naf
03-19-09, 09:37 AM
Naf...you should take a trip out to Tel Aviv today to show me your car...I know everyone here would love someone to get a first hand look at your work of art!

Although...i don't know if thats even an option in this part of the world these days...

You are in Isreal? Why dont you hop over to my neck of the woods...

I would get in trouble enterin Isreal. The middle eat officials mainly are small minded and dont like them very much..I get my passport stamped from them could spell harshship movin around for me...

i could meet u in DXB and we can hit the track a little for some fun...

Slithering_Joe
03-19-09, 09:38 AM
Let the 'modification-master-bation' begin.....again.

SkullV
03-19-09, 09:40 AM
You are in Isreal? Why dont you hop over to my neck of the woods...

I would get in trouble enterin Isreal. The middle eat officials mainly are small minded and dont like them very much..I get my passport stamped from them could spell harshship movin around for me...

i could meet u in DXB and we can hit the track a little for some fun...

Yeah, I figured it would be trouble for you to get here. I am just on vacation here so no V....my brother has a stamp from Jordan and they give him crap every time he tries to get back into Israel

PISNUOFF
03-19-09, 10:11 AM
I want my exhaust to come out of my rocker panels. Naf - are you having someone look into making a kit for this also? That would be sweet! Would help you out on your weight loss program also, no mufflers or piping to the rear fascia.

Naf
03-19-09, 10:53 AM
Yeah, I figured it would be trouble for you to get here. I am just on vacation here so no V....my brother has a stamp from Jordan and they give him crap every time he tries to get back into Israel

Its children fightin...Both are too small minded to accept the other...

In regards to the side exits, i would have clearance issues, sowwy no go for me...

rjoffe
03-19-09, 11:09 AM
So let's talk technical for a moment. If you had the ideal rear diffuser, what sorts of gains would you expect to see ?

Naf
03-19-09, 11:18 AM
Well, the main thing would be better down froce on high speed corners...Also better grip at high speed without havin to go with a more "aggressive" rear spoiler....

The one thing i have noticed is when i get above 120mph i feel the back end kickin out slightly on those long turns and the Stability program kicks in on those power straights...

It would only count if you are at high speeds the most, kinda like the rear tower strut. It works only when you start takin the corners more aggressively. For the daily drivers or weekend warriors this may be overkill...

Naf
03-19-09, 11:39 AM
Taken from APR Performance website (http://www.aprperformance.com/index.php?option=com_content&task=view&id=135&Itemid=44)

Diffusers

What is a diffuser:
A diffuser is a shaped part of a car's body, usually found in the underside of the car. It can be located at the rear underside, or closer to the front underside near the wheel wells. A rear diffuser is typically sloped upward from front-to-back, and may have vertical fins attached to the bottom of the sloped surface. The rest of this article will apply, for the most part, to the rear diffuser.

The diffuser has two (2) purposes:
1. To reduce drag.
2. To reduce lift.

What goes on at the rear-end of a car:
The area immediately behind the car tends to have turbulent, slow-moving air. The fast underbody air that exits the car ends up meeting with this slow-moving outside air. The greater the air speed difference is, the more turbulence is created. This turbulence causes unwanted drag and disrupts the airflow that exits from the underbody, which in turn decreases the underbody's ability to reduce lift.

How the diffuser works:
The diffuser itself does not actually create downforce - it works in conjunction with other aerodynamic components to reduce drag and lift. The upward front-to-back angle of the rear diffuser causes the fast-moving underbody air to expand and slow down. This slower air is then better able to meet up with the slow outside air, thus reducing the amount of turbulence behind the car. The vertical fins are there to make sure that the air at the rear left and right sides do not disturb the function of the diffuser.


When is a diffuser effective:
As a general guideline, the rear diffuser needs to be angled upward at least 10 degrees. In order for a rear diffuser to be effective, the air that travels under the car from the front needs to be as fast and smooth as possible. Slow-moving, turbulent air is not going to help a diffuser do its job.

In order to create the smooth air that the diffuser needs, it is recommended that the car have a flat undertray (a.k.a. underbody) that covers most of the uneven surfaces and components on the cars bottomside. However, production road cars typically do not have, or only partially have, an area that is covered by a flat undertray.

rjoffe
03-19-09, 11:43 AM
It would seem to me, that whatever solution you come up with needs to be validated either in a wind tunnel, or by using some measurement (suspension compression, etc). Otherwise you may not be achieving your goals. Do you have any plans to verify the effectiveness of the solution you finally settle on ?

Naf
03-19-09, 11:47 AM
I am goin to wait till i get the product in hand. The manufator will have recommended angles of attack with predicted downforces. i will then have to do a trial and error till i get happy with the returns...i have already come to the conclusion of how much rear bumper i am willin to sacrifice for the greater good...Till the bottom of the double line

Theories and equations do not eqaul real life trials. As long as i am happy its all justified.

814V
03-19-09, 01:17 PM
i wanna see a pic of one on a V

then i will say my final answer.. the diffuser looked sexy on my wrex

thebigjimsho
03-19-09, 03:09 PM
Its such with an H not a k...


No, I think he got it right...

ctsv154
03-19-09, 03:23 PM
Without the underbelly panels, I cant see a rear diffuser really doing much. It may help the turbulant air escape better but the whole point of the belly panels and diffuser are to keep the air clean.



You really dont know?

A rear diffuser is one of the best downforce enhancers with the least amount of drag...You can always slap on MASSIVE rear wing but you will have AMPLE drag on the car at high speeds and unneeded downforce at low speed...(though the rooster tail of rain water behind u is always a grin pleaser...)
The fins on the rear diffuser help direct the Vacuumed air in a straight line so you stay true and straight.

I like the one from the SRT but i see no angle where the vehicle causes a vacuum under the car? Normally you will see an elevation towards the rear of the diffuser.
To be honest the only one i really like is the VIS one...The other two are too much style then performance...



When is a diffuser effective:
As a general guideline, the rear diffuser needs to be angled upward at least 10 degrees. In order for a rear diffuser to be effective, the air that travels under the car from the front needs to be as fast and smooth as possible. Slow-moving, turbulent air is not going to help a diffuser do its job.

In order to create the smooth air that the diffuser needs, it is recommended that the car have a flat undertray (a.k.a. underbody) that covers most of the uneven surfaces and components on the cars bottomside. However, production road cars typically do not have, or only partially have, an area that is covered by a flat undertray.



Umm........ I told you???

The Tony Show
03-19-09, 03:27 PM
"Hello to more rear downforce"? At what speeds do you think this thing will actually function? Unless you seal off the whole undercarriage AND are going 100+ on a race track, the rear diffuser will be useless.

I'm not one to normally criticize other people's taste in mods, but I'm flabbergasted at how you somehow always seem to find the most expensive, least productive modifications to do to your car.

ctsv154
03-19-09, 03:32 PM
"Hello to more rear downforce"? At what speeds do you think this thing will actually function? Unless you seal off the whole undercarriage AND are going 100+ on a race track, the rear diffuser will be useless.

I'm not one to normally criticize other people's taste in mods, but I'm flabbergasted at how you somehow always seem to find the most expensive, least productive modifications to do to your car.

:histeric:

thebigjimsho
03-19-09, 04:00 PM
tehehe...

rjoffe
03-19-09, 04:02 PM
So since we are discussing the diffuser, what would be the difficulties in fabricating and installing an underbody tray? Has anyone headed down that path yet ? Did the racing V's have anything similar done ?

SoJersey05V
03-19-09, 05:08 PM
yea the one naf has picked out belings on the front wheel drive hondas!

Oleksakjr
03-19-09, 06:12 PM
Is this a joke? Seriously?

Come on man...

thebigjimsho
03-19-09, 11:35 PM
Didn't the old Chaparral 2J use fans to suck the air out from under the car? why not do that and trump all?

ctsv154
03-19-09, 11:41 PM
The ultimate rear diffuser!

http://www.ultimatecarpage.com/images/large/91-3.jpg

thebigjimsho
03-20-09, 12:00 AM
Use the trunk to house the dual snowmobile engines...

atdeneve
03-21-09, 07:21 PM
While I do applaud your initiative, Naf, I'm a bit more partial to ctsv154's diffuser choices on the Viper and the Enzo.

I've also asked around about this and would like to eventually get a set fabbed up, so if you make some headway, all the better. Yeah, we'll need to get the rest of the underbelly paneled up, but that's relatively easy. It's all just flat panels fit to size. Not a lot of fab work. Just pay for some nice carbon.

So do us all a favor and pick a diffuser that is a bit more discrete. Something along the lines of what ctsv154 posted would be nice...
http://img84.imageshack.us/img84/9071/ferrarienzoyn4.jpg

CTS-Voodoo
03-21-09, 07:46 PM
Plus without the underbelly panels, I cant see a rear diffuser really doing much. It may help the turbulant air escape better but the whole point of the belly panels and diffuser are to keep the air clean.

Ding! Without smoothing the entirety of the bottom of the car rear diffusers wont do much for aerodynamics. That and if you do end up buying one of those diffusers that sticks out off the side of the body, do yourself a favor and saw your engine block in half, cause youre no better than the ricers. :stirpot:

ccextra1976
03-21-09, 07:58 PM
Naf,

I doubt you are going to pnl the whole underside of your car, so mainly it will be for looks...

this being the case instead of cutting the bumper cover etc...why not just make a template from the factory bumper to the rear of the diff? make a mold template out of wood with your fins etc...then lay the carbon/resin trim it up and make attachments to the factory bumper/spare tire pan etc...poof done!

atdeneve
03-21-09, 08:26 PM
S'why I have extra front and rear bumpers...

AAIIIC
03-21-09, 08:48 PM
There are plenty of production-based race cars that have functional rear diffusers without creating an entire flat bottom. The flat bottom makes it more effective, but it's not a requirement in order to have a diffuser create useful downforce (or at least reduce lift, as the case may be). With that said, it should be pretty easy to create a flat bottom on the CTS, as the underside of the car is pretty uncluttered. I wouldn't go about doing an entire flat floor with CF, though, as there are other, much more affordable materials that one could use. This is Naf, though, so maybe the most expensive route is best. :p

I think the idea of running the rear diffuser in lieu of a rear wing and getting similar downforce is horribly optimistic. Cars like the Ferrari that has been posted a couple of times now were designed with that goal in mind from the start. I don't think you could tack on a diffuser to a car that wasn't designed with that in mind to begin with and expect to see results anywhere near the same. And even that Ferrari gets a big ass rear wing when it goes racing (as it is right now in the 12hr of Sebring).

thebigjimsho
03-21-09, 10:12 PM
Just slap on a big ass wing and be done with it. carbon fiber for lightness...

ctsv154
03-21-09, 10:38 PM
Dont forget the Ti hardware!

ccextra1976
03-21-09, 10:49 PM
Dont forget the Ti hardware!

:histeric: just think naf...if you took out the carpet in the trunk...the under hood panel the FRC's you would save about $2K in Ti hardware cost..:canttalk:

thebigjimsho
03-21-09, 10:54 PM
tru dat

04vman
03-21-09, 11:16 PM
I think the G8 GXP rear diffuser would look the nicest on our cars.

BacDoc
03-21-09, 11:34 PM
Rice, rice, baby.

thebigjimsho
03-21-09, 11:52 PM
beaten to deth...

Naf
03-22-09, 01:44 AM
:histeric: just think naf...if you took out the carpet in the trunk...the under hood panel the FRC's you would save about $2K in Ti hardware cost..:canttalk:

Well, just for the record, i had to remove the engine cover for it wasnt fittin over my MSD coils. Most of the hardware holdin the everything minus the heads (for the time being includin the pushrods) in place are Ti...In the rear there isnt much i can do except trim the wheel well.

Have to admit plenty of acceleration all over the place, but my stability kicks in at high speeds even though its off..I think it has to do with the fact i dont have cruise control any more in 5th oor 6th gear...

Needless to say, it will all be justified once i start passin cars that are above my class...

thebigjimsho
03-22-09, 02:13 AM
Well, just for the record, i had to remove the engine cover for it wasnt fittin over my MSD coils. Most of the hardware holdin the everything minus the heads (for the time being includin the pushrods) in place are Ti...In the rear there isnt much i can do except trim the wheel well.

Have to admit plenty of acceleration all over the place, but my stability kicks in at high speeds even though its off..I think it has to do with the fact i dont have cruise control any more in 5th oor 6th gear...

Needless to say, it will all be justified once i start passin cars that are above my class...No one is above your class. You are classless...

Naf
03-22-09, 02:56 AM
Are you insultin me by sayin i have no class, or that fact i am classed in a classless section...?

Oleksakjr
03-22-09, 02:03 PM
maybe both

thebigjimsho
03-22-09, 07:00 PM
Are you insultin me by sayin i have no class, or that fact i am classed in a classless section...?
It's a replay of one of my favorite Family Guy quotes from the episode: Death Lives.


Carter: What the hell are you doing here?
Peter: It's a long story with some terrific performances and a wonderful scene at a carnival, but I'll cut to the ending. I want to marry Lois!
Carter: Out of the question! Now, listen, Griffin. I want you to take this, and stay away from my daughter forever!
Peter: $1 million?
Carter: $1 million.
Peter: No deal! Lois may be worth a million to you, but to me, she's worthless. I love her, Mr. Pewterschmidt.

Naf
03-23-09, 03:23 AM
maybe both

:thehand: Dont add to the fire...:thehand:

You will drop the ball, and i will be waitin for you...

UnsafeAtAnySpd
03-23-09, 04:35 AM
Do you mean soap?

Naf
03-23-09, 04:52 AM
Do you mean soap?

You may swing that way, but that is not my style...

trukk
03-23-09, 03:47 PM
Interesting read.

I actually plan to do this at one point or another, but not until my car is a dedicated track mule.

Some moron rear ended my on 95 a few monts back, and cracked my rear facia. I have to get a new one anyway, so I will save my old one, and hack it up. I certainly wasn't thinking carbon fiber, more like bent aluminum sheets held on my pop rivets :D (or something to that effect). Unless I eff it up REALLY bad, I can't see it doing any harm, and it would be cheap, so WTF.

At that point anyway I will hack the entire spare tire well out. No reason that I can think of not to use that area for the diffuser. I sure it will look horridible though :thumbsup: Look at the eagle wing on V-Sams car though, ugly as hell, but effective.

I wouldn't do this on a street car.

Finally as with most of Naf's ideas this is fairly half baked. I am interested to see what he comes up with though.

-Chris

Cadillac Tony
03-23-09, 06:31 PM
If you want to reduce rear lift at speed and are willing to hack up the trunk, just do what they did to the World Challenge V and run a giant scoop underneath the car where the spare tire well is (was), and feed it out the back of the trunk by cutting out the rear license plate area.

Let me see if I can dig up a pic I took at Sebring.....

mgscustomtune
03-23-09, 08:44 PM
Naf l think its great idea someone thinking outside the box. I am always looking for such ideas. That is what this form is all about to share our ideas with the masses.

thebigjimsho
03-23-09, 11:03 PM
aww, don't lead him along...

UnsafeAtAnySpd
03-24-09, 01:51 AM
Just do it and then post pics. Oh yeah, buy a better camera first though.

Naf
03-24-09, 02:51 AM
I talked the to seller for the VIS one, and he doesnt do business with international PAYPAL holders...Kiss akhto biary akho sharmoota...I asked a friend of mine in Boston to close the deal for me...

This bites...

Also PST arent talkin to me in any regards to the CF driveshaft. They are lookin for any excuse not to makin one yet BMR contracted them to make the single peice one in 05...Someone here has to have the CF DS...

And my ideas arent half baked, they are just so out of the box....

thebigjimsho
03-24-09, 08:53 AM
out of the box? :rolleyes:

trukk
03-24-09, 09:20 AM
If you want to reduce rear lift at speed and are willing to hack up the trunk, just do what they did to the World Challenge V and run a giant scoop underneath the car where the spare tire well is (was), and feed it out the back of the trunk by cutting out the rear license plate area.

Let me see if I can dig up a pic I took at Sebring.....


Tony,

I remember those pictures. I believe they were there for the diff cooler that they installed in the spare tire well, and then vented the air out the rear facia. I think their approach was two fold in that regard (i.e. 'difuse' the air to some extent, and get fresh air on the diff radiator.)

-Chris

atdeneve
03-24-09, 09:35 AM
Out of the box? I'd say there are, at least, a handful of people here that were most likely already looking into this. Your end result may be a bit (or, in your case, a lot) different, yes, but the initial seed of the idea itself, is hardly outside the box. Dude, no ideas original...

It's never what you do, but how it's done. Just make sure it's not done with your initial choice for a diffuser.

rjoffe
04-15-09, 10:57 AM
Interesting talk about diffusers for those interested.

http://formula-one.speedtv.com/article/matchett-malaysian-gp-chalk-talk

thebigjimsho
04-16-09, 12:02 PM
Interesting talk about diffusers for those interested.

http://formula-one.speedtv.com/article/matchett-malaysian-gp-chalk-talk
group buy!