Welcome to the North American Subaru Impreza Owners Club Saturday December 3, 2016
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Go Back   NASIOC > NASIOC General > Motorsports

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads. 
Reply
 
Thread Tools Display Modes
Old 01-07-2006, 06:35 PM   #1
Type1
Scooby Specialist
 
Member#: 19412
Join Date: May 2002
Location: San Diego, CA
Vehicle:
2002 Rex
Bling Bling silver

Default Undercarriage diffuser/spoiler - serious input

So ive been at my new job now for about 3 weeks (a ferrari/lamborghini/maserati dealership and shop and yes ive got to push alot of them) http://www.bobileff.com and ive seen probably all types/years/models of these cars and what ive noticed is that starting from the early models all of the ferraris undercarriages are covered up. Espeically the new ones obviously with all the technology there is alot of R&D that goes into these underbody spoilers.

Anyway I know the new 06 STi has some new "covers" or whatever you want to call them but in my opinion they are really to small to make a difference, I know its there but I dont think its enough.

This monday im going to an steel/aluminum shop with one of the shop welders cause he has to pick up material to make a new table and since im there I was thinking of buying some sheets of aluminum to possibly make a full underbody cover/diffuser.

Im going to copy some designs of the ferraris and stuff where they leave the sections of the exhausts open to release heat, and cut slits where the engine bay is to further release heat, etc..

I was wondering if anyone has attempted this cause I could use some help. The other mechanics at the shop are willing to help me and ill probably do this before or after my shifts and I have access to all the tools in the world.

So if anyone can tell me anything before attempting this I will be really grateful. If you think this is a bad idea tell me too also but give me a reason...not just "thats ****s rice."

Thanks!
* Registered users of the site do not see these ads.
Type1 is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 01-07-2006, 07:05 PM   #2
racerjon1
Scooby Specialist
 
Member#: 43612
Join Date: Sep 2003
Location: Columbia, SC
Default

Other than the Formula cars I race.. I dont have experience with building a flat bottom for one.

But I will soon.

The issues I am coming up with is material, how to attach it, cooling, design.

Remember the Ferrari and such are designed on a program, soildworks run through fluidworks or something even more specailized. They also have moving ground wind tunnels to test stuff on.

My first thought was to just build a flat bottom for the car, with a basic diffuser (break where you want the most downforce, no more than 7' upsweep) The problem with this is, there is some optimum length for laminar flow and if its too long then you can have turbulance before the break point of the diffuser and it wont be as effective, so there are considerations there, and also, a pure flat bottom without tunnels is sensetive to pitch.

I will be seeing speeds in the 170-180 range at times, so I am slightly worried about that whole pitch issue. (I dont want no acrobatics)

The other thing i am trying to consider is method of attachment, my F2000 diffuser when i first put it on despite having brackets and attachment front and rear, flexed and pulled itself into the track. (it was a honycomb center carbon build as well) So we had to add another center attachment point. If things go well and you develop enough downforce, then there is a chance it all gets ripped out the bottom..

So.. thats where I stand.

Jon
racerjon1 is offline   Reply With Quote
Old 01-07-2006, 09:51 PM   #3
BIGSKYWRX
Scooby Guru
 
Member#: 7958
Join Date: Jul 2001
Location: Plains of Eastern Montana
Vehicle:
09 GH B+

Default

The STi has continued to add more and more in the way of under aero bits

BIGSKYWRX is offline   Reply With Quote
Old 01-07-2006, 10:35 PM   #4
darksands
Scooby Specialist
 
Member#: 75122
Join Date: Nov 2004
Chapter/Region: SCIC
Location: Im in a glass case of emotion
Vehicle:
2005 Impreza WRX
Crystal Gray

Default

^^^
That doesnt look like a USDM STi.
darksands is offline   Reply With Quote
Old 01-07-2006, 10:43 PM   #5
godai
Scooby Newbie
 
Member#: 19744
Join Date: Jun 2002
Default

Quote:
Originally Posted by darksands
^^^
That doesnt look like a USDM STi.
how so?
godai is offline   Reply With Quote
Old 01-07-2006, 10:44 PM   #6
afpdl
Scooby Guru
 
Member#: 26361
Join Date: Oct 2002
Chapter/Region: TXIC
Location: Sugar Land (Houston), Tx
Vehicle:
My shenanigans are
cheeky and fun

Default

Quote:
Originally Posted by darksands
^^^
That doesnt look like a USDM STi.
In what way?
afpdl is offline   Reply With Quote
Old 01-08-2006, 12:02 AM   #7
MPME
Scooby Specialist
 
Member#: 85176
Join Date: Apr 2005
Chapter/Region: BAIC
Vehicle:
2006 Scion tC

Default

I have a somewhat recent article that covers this exact topic--if it doesn't answer your questions, let me know and I'll gladly help. It has pictures of an '05 STi Cusco front splitter/aluminum floor install I did as well.

http://www.tprmag.com/issue/13/13_aerodynamics.shtml

The part 2 of the feature is due out in a month or two months, and covers road racing aero for tuner/import car specifically, and might have more direct info for you.
MPME is offline   Reply With Quote
Old 01-08-2006, 01:35 AM   #8
Homemade WRX
Scooby Guru
 
Member#: 33782
Join Date: Mar 2003
Chapter/Region: MAIC
Location: 3MI Racing LLC
Vehicle:
96 bastard child
search FIRST, then PM!!!

Default

it will make a difference with drag, if not with downforce...I've been looking into making one for my car and another local...it is actaully quite simple to do, I just need to time and money now...
I've only looked into doing the front bumper to the firewall (area) and under cabin area...the rear I imagine would be quite simple though.

Last edited by Homemade WRX; 01-08-2006 at 02:45 AM.
Homemade WRX is offline   Reply With Quote
Old 01-08-2006, 02:07 AM   #9
Patrick Olsen
NASIOC Supporter
 
Member#: 120
Join Date: Jul 1999
Chapter/Region: AKIC
Location: Where the Navy sends me...
Vehicle:
1997 Legacy 2.5GT
QuickSilver Metallic

Default

No offense, Homemade, but there's absolutely nothing simple about designing any sort of aerodynamic device. You could just put a flat plate back there, and that would be simple, but it would also be completely ineffective and may actually hurt the airflow around/under the car.

Type1, I'd say your best bet is to start by duplicating what's been done on the '06 STi. The problem will be determining any effect of what you add to the car. At least if you roughly copy the STi bits you'll know that you're working in the right direction. Just be ready for it to be an iterative process - you may need to refine/redesign your parts as you go along.

Definitely has the potential to be a neat project. Keep us informed.

Pat Olsen
'97 Legacy 2.5GT sedan
Patrick Olsen is offline   Reply With Quote
Old 01-08-2006, 02:24 AM   #10
Homemade WRX
Scooby Guru
 
Member#: 33782
Join Date: Mar 2003
Chapter/Region: MAIC
Location: 3MI Racing LLC
Vehicle:
96 bastard child
search FIRST, then PM!!!

Default

Quote:
Originally Posted by Patrick Olsen
No offense, Homemade, but there's absolutely nothing simple about designing any sort of aerodynamic device. You could just put a flat plate back there, and that would be simple, but it would also be completely ineffective and may actually hurt the airflow around/under the car.
trust me I know more than you think I do...just got done building and testing (8 different models) our 1/2 scale model for our Formula SAE car...I have also taken 3 400 level aerospace courses, one specifying in ground vehicle aerodynamics. I'm also lined up to get an internship at Langley full scale windtunnel...and when I said it's easy, I was referring to mounting...there are plenty of nuts, bolts and open spaces to mount to on the bottom of our cars.
as for the flat plate covering the spare, that actually reduces the turbulent flow of air (causing drag) coming from the back of you car...have the test numbers from a ford taurus where it was done.
-Micah
Homemade WRX is offline   Reply With Quote
Old 01-08-2006, 02:35 AM   #11
bemani
Scooby Specialist
 
Member#: 5673
Join Date: Apr 2001
Location: Folsom, CA
Vehicle:
16 Hellcat
05 LGT, 02 bug eye

Default

Quote:
Originally Posted by godai
how so?
Undercover for the transmission?
bemani is offline   Reply With Quote
Old 01-08-2006, 03:35 AM   #12
afpdl
Scooby Guru
 
Member#: 26361
Join Date: Oct 2002
Chapter/Region: TXIC
Location: Sugar Land (Houston), Tx
Vehicle:
My shenanigans are
cheeky and fun

Default

Quote:
Originally Posted by bemani
Undercover for the transmission?
Added in 06 along with the diffuser.
afpdl is offline   Reply With Quote
Old 01-08-2006, 04:31 AM   #13
Imprezanator
Scooby Newbie
 
Member#: 1586
Join Date: Jun 2000
Location: Up Butler, PA USA
Vehicle:
2003 WRX
Platinum Silver Metallic

Default

Quote:
Originally Posted by godai
how so?

The exhaust is coming down on the left side of the car and exiting out the right in the rear, instead of vice-versa for LHD cars.


Alot of those under-body panels are for sound dampening.
Imprezanator is offline   Reply With Quote
Old 01-08-2006, 04:35 AM   #14
afpdl
Scooby Guru
 
Member#: 26361
Join Date: Oct 2002
Chapter/Region: TXIC
Location: Sugar Land (Houston), Tx
Vehicle:
My shenanigans are
cheeky and fun

Default

No its not, the downpipe is on the left side and the muffler is on the right, the car is upside down. And LHD cars have the same exhaust set up anyway.
afpdl is offline   Reply With Quote
Old 01-08-2006, 05:29 AM   #15
Ver.III
Scooby Specialist
 
Member#: 1185
Join Date: Mar 2000
Location: North of the border
Vehicle:
I flap my gums
and now I'm a specialist

Default

Its JDM. That pic shows no mid-cat . Just 2 resonators.
Ver.III is offline   Reply With Quote
Old 01-08-2006, 06:49 AM   #16
AUTOwrXER
Scooby Specialist
 
Member#: 5817
Join Date: Apr 2001
Location: Atlanta, GA, USA
Vehicle:
2005 STi
Silver

Default

Quote:
Originally Posted by BIGSKYWRX
The STi has continued to add more and more in the way of under aero bits

So that's where all the extra weight comes from...
AUTOwrXER is offline   Reply With Quote
Old 01-08-2006, 11:06 AM   #17
makofoto
Scooby Guru
 
Member#: 25243
Join Date: Sep 2002
Chapter/Region: SCIC
Location: South Pasadena, CA
Vehicle:
2006 Legacy Outback
Blue

Default

What are you going to be doing with your car that you feel you would benefit from this project?
makofoto is offline   Reply With Quote
Old 01-08-2006, 12:27 PM   #18
BIGSKYWRX
Scooby Guru
 
Member#: 7958
Join Date: Jul 2001
Location: Plains of Eastern Montana
Vehicle:
09 GH B+

Default

That is a pic of the jdm car, but as has been pointed out now the same underside as the 06 usdm, 05 so the addition of the two side bits, 06 the rear diffuser (and evidently the tranny one as well- didn'ty know the 06 usdm got this one).

Several have added the rear diffuser w/o much hassle, a couple have added the side bits- requires drilling.

What I found interesting was that although no one could provide emperical data on downforce changes, etc- they did report a mile or two/ gallon improvement in fuel consumption

These are plastic bits, so there isn't too much in the way of increased weight.
BIGSKYWRX is offline   Reply With Quote
Old 01-08-2006, 01:44 PM   #19
Type1
Scooby Specialist
 
Member#: 19412
Join Date: May 2002
Location: San Diego, CA
Vehicle:
2002 Rex
Bling Bling silver

Default

Quote:
Originally Posted by makofoto
What are you going to be doing with your car that you feel you would benefit from this project?
Well I used to be really into rallying, actually I still am but the cost of replacing stock shocks and going through tires is starting to add up. I got a deal on some KYB's a while back and have them on now and from what I hear from everyone its super easy to blow them doing what I do and I cant afford those DMS rally shocks for 5 grand. I also recently got sponsored by dunlop and currently I only have 1 set of wheels and tires and I dont want to wreck them cause I need them for shows so basically the only thing im left with is autocrossing and track time. Since im in san diego im not too far from buttonwillow or other semi-local tracks and I just thought it would be a cool idea to make somethin like this for my car since I basically have all the tools, material, and knowledge in my hands. I was planning to make myself some skidplates anyway so why not just do this right? And im not concerned with downforce im looking for less drag.

I remember watching an old episode of car and driver about 2 years ago and at that time one of the lexus sedan cars I forget which one had the lowest drag coefficient compared to other cars and this was attributed to a full undercarriage cover. A freakin boat lexus had the lowest drag coef. can you believe that? And I know there is a lot of R&D that goes into it but I dont mind test fitting my car..its a work in progress. Maybe after this project if im still working at this gig Ill have my whole car stitch welded...rally style
Type1 is offline   Reply With Quote
Old 01-08-2006, 02:15 PM   #20
richde
Scooby Specialist
 
Member#: 79498
Join Date: Jan 2005
Chapter/Region: SWIC
Location: SCIC's trashy neighbor
Vehicle:
2013 XV

Default

Quote:
Originally Posted by AUTOwrXER
So that's where all the extra weight comes from...
That's probably 20 pounds of plastic/fasteners, MAX. I'd think the extra weight comes from the tranny and misc chassis stiffening bits, like the part behind the rear seat.

All the info to do it, part #'s and basic instructions, is here: http://forums.nasioc.com/forums/showthread.php?t=889855
richde is offline   Reply With Quote
Old 01-08-2006, 02:30 PM   #21
richde
Scooby Specialist
 
Member#: 79498
Join Date: Jan 2005
Chapter/Region: SWIC
Location: SCIC's trashy neighbor
Vehicle:
2013 XV

Default

Quote:
Originally Posted by afpdl
No its not, the downpipe is on the left side and the muffler is on the right, the car is upside down. And LHD cars have the same exhaust set up anyway.
I think the negative got reversed and nobody noticed along the way, since JDM engines are the same as USDM as far as exhaust routing goes.

Afpdl get's an "A" in Attention to Detail!
richde is offline   Reply With Quote
Old 01-08-2006, 02:37 PM   #22
Calamity Jesus
Scooby Guru
 
Member#: 44501
Join Date: Oct 2003
Chapter/Region: South East
Location: in a minefield of caddishness.
Vehicle:
1984 That's *Sir*
Weinerlicks of Douche 2u.

Default

Quote:
Originally Posted by Type1
I remember watching an old episode of car and driver about 2 years ago and at that time one of the lexus sedan cars I forget which one had the lowest drag coefficient compared to other cars and this was attributed to a full undercarriage cover. A freakin boat lexus had the lowest drag coef. can you believe that?
Sure I can believe that. Drag coefficient is a 'coefficient' because it's only a part of the whole story. You need to multiply the coef. by the frontal area (the area of the car if you were too look at it from straight on as a silhouette) of the car to determine the actual amount of drag. Something like a corvette, with very little frontal area and a similarly low drag coefficient would produce much less actual drag than the 'freakin boat' of a lexus.
Calamity Jesus is offline   Reply With Quote
Old 01-08-2006, 04:26 PM   #23
endeavor
Scooby Specialist
 
Member#: 60740
Join Date: Apr 2004
Chapter/Region: South East
Location: Durham, NC
Vehicle:
2004 Impreza WRX
Silver

Default

One other thing too, race cars are designed to produce downforce, not just have low drag; downforce is created with drag. So a C6 Z06, Viper, or F1 car will have a higher Cd than a Lexus or other sedans. I'm not sure which would actually have the higher net drag. (i.e. does the smaller frontal area make up for the higher Cd.)
endeavor is offline   Reply With Quote
Old 01-08-2006, 04:59 PM   #24
speedyHAM
Scooby Specialist
 
Member#: 48377
Join Date: Nov 2003
Chapter/Region: MWSOC
Location: "They eat fish soaked in lye"
Vehicle:
1996 Gutted, built
XP class Impreza L

Default

Quote:
Originally Posted by endeavor
One other thing too, race cars are designed to produce downforce, not just have low drag; downforce is created with drag. So a C6 Z06, Viper, or F1 car will have a higher Cd than a Lexus or other sedans. I'm not sure which would actually have the higher net drag. (i.e. does the smaller frontal area make up for the higher Cd.)
Race cars that produce downforce typically have a horrible Cd and net drag ratings. A C5R corvetter for instance has a Cd of .37 vs. a Cd of .28 for the production Z06. An F1 car is setup purely for efficient downforce, drag is a secondary concern. Those things with almost 1000 Hp had a top speed of around 250 mph, with a much sleeker body and 375 less Hp a Mclaren F1 had a top speed of 245. The smaller frontal area makes no difference when you are talking about that much downforce.

A flat bottom to our cars would help the overall fuel economy, but not enough to be cost effective for Subaru. Those little plastic peices and fasteners + assembly time add up to a lot on a per car basis. I'd like to make one but don't have the money or the time.

As far as the laminar flow underneath the car- it stops at the end of your front bumper. To get it past the front wheels would be practically a miracle with a smooth bottom. If you are really interested in doing this pick up a book called "Race Car Aerodynamics" it is the best book out there on the subject from an overall standpoint. It has more usefull information than anyone here could spit out.
speedyHAM is offline   Reply With Quote
Old 01-08-2006, 06:18 PM   #25
racerjon1
Scooby Specialist
 
Member#: 43612
Join Date: Sep 2003
Location: Columbia, SC
Default

There is another thing to consider in designing a bottom like this fro street car vs race car.. Heat buildup.

A Racecar that is going to run for short periods, and/or be rebuilt following an event doesn't have to worry about this in the same way that a street car that is going to plan ot be run for 100k+ miles. When you consider a Subaru with differentials and such, there is a lot of heat that can cause problems.

"Production" Flat bottoms such as Ferrari and Lamborghini and such are actually not flat, they have tunnels, and either channels that rout air out the side that is turbulant (such as that caused by the tires) or tunnels that rout it back out through the diffuser. (example, Ferrari 360)

The Lotus Elise actually has the kind of flat bottom that we are talking about (big sheets of aluminum) followed by a diffuser. It is probably pratical in terms of fuel economy, and aids in reducing lift, but actually producing downforce per se is going to be higly unlikely withough some serious expertise/computer/wind tunnel time.

This isn't bad of course, modern cars produce from 200-750lbs of lift at 120 mph, and a reduction of that would be good.

Jon K
racerjon1 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
GD "EVO" Diffuser / spoiler Layvon Exterior/Styling 3 03-28-2010 02:35 PM
Serious question, input needed (tattoos, ttiwwop will be satisfied) TVA Off-Topic 65 01-04-2009 05:05 PM
Need some input. Possible damage to undercarriage. :( DilferJr General Community 9 09-01-2006 03:09 PM
06 Undercarriage Air Diffuser! OEM DECALFX Private 'For Sale' Classifieds 12 03-09-2006 02:38 PM
OT Frequent Flyers. I need your serious input. Sharkbait Off-Topic 8 12-15-2005 03:37 AM

All times are GMT -4. The time now is 07:37 AM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2016, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2016 Axivo Inc.
Copyright ©1999 - 2016, North American Subaru Impreza Owners Club, Inc.