Fabrication Custom fabrication ideas and concepts ranging from body kits, interior work, driveline tech, and much more.

Rear Diffuser

Old 04-04-2009, 01:09 PM
  #1  
Member
Thread Starter
iTrader: (5)
 
strc09's Avatar
 
Join Date: Mar 2005
Location: Displaced Texan living in NC
Posts: 263
Likes: 0
Received 0 Likes on 0 Posts
Car: 1988 Pontiac Firebird Trans AM GTA
Engine: Tune-port Injected 6.3L
Transmission: Borg-Warner T56 six-speed
Axle/Gears: Borg/Warner 9-bolt with 3.70:1
Rear Diffuser

I did a search through the TGO forums and didn't really find what I was looking for. Has anyone ever made a diffuser for their Camaro or Firebird before? I'm looking for some specs and list of materials. From what I've been reading it'll help out and help keep my rear planted going down the road. I've found a site that sells splitters for the front and sides, but no diffusers. Plus they look pretty cool.

Any help would be appreciated.
strc09 is offline  
Old 04-04-2009, 02:22 PM
  #2  
Moderator
 
AlkyIROC's Avatar
 
Join Date: Jul 1999
Location: 51°N 114°W, 3500'
Posts: 16,738
Likes: 0
Received 3 Likes on 2 Posts
Car: 87 IROC L98
Engine: 588 Alcohol BBC
Transmission: Powerglide
Axle/Gears: Ford 9"/31 spline spool/4.86
Re: Rear Diffuser

Diffuser? What's that?
AlkyIROC is online now  
Old 04-04-2009, 02:56 PM
  #3  
Member
Thread Starter
iTrader: (5)
 
strc09's Avatar
 
Join Date: Mar 2005
Location: Displaced Texan living in NC
Posts: 263
Likes: 0
Received 0 Likes on 0 Posts
Car: 1988 Pontiac Firebird Trans AM GTA
Engine: Tune-port Injected 6.3L
Transmission: Borg-Warner T56 six-speed
Axle/Gears: Borg/Warner 9-bolt with 3.70:1
Re: Rear Diffuser

One of these...
strc09 is offline  
Old 04-04-2009, 03:20 PM
  #4  
Senior Member
iTrader: (21)
 
82 Iron Duke's Avatar
 
Join Date: Dec 2005
Posts: 4,075
Likes: 0
Received 0 Likes on 0 Posts
Car: 04 Silverado
Engine: 4.8
Transmission: auto
Re: Rear Diffuser

That looks more like a deflector
82 Iron Duke is offline  
Old 04-04-2009, 03:27 PM
  #5  
Moderator
iTrader: (5)
 
JamesC's Avatar
 
Join Date: Aug 1999
Location: Lawrence, KS
Posts: 19,118
Likes: 0
Received 0 Likes on 0 Posts
Car: Met. Silver 85 IROC
Engine: 350 HO Deluxe (350ci/330hp)
Transmission: T-5 (Non-WC)
Axle/Gears: Limited Slip 3.23's
Re: Rear Diffuser

Or a truncated belly pan. I wonder what kind of speed would be involved for the piece to be of benefit?

JamesC
JamesC is offline  
Old 04-04-2009, 03:40 PM
  #6  
Member
Thread Starter
iTrader: (5)
 
strc09's Avatar
 
Join Date: Mar 2005
Location: Displaced Texan living in NC
Posts: 263
Likes: 0
Received 0 Likes on 0 Posts
Car: 1988 Pontiac Firebird Trans AM GTA
Engine: Tune-port Injected 6.3L
Transmission: Borg-Warner T56 six-speed
Axle/Gears: Borg/Warner 9-bolt with 3.70:1
Re: Rear Diffuser

It mounts under the rear bumper to deflect the air so that it isn't so turbulent as it exits from under the car and joins with the air that flows over the top. They're generally on high-end sports cars, but do have benefits on other cars just because of what I mentioned previously.

http://www.aprperformance.com/index....=214&Itemid=44
strc09 is offline  
Old 04-04-2009, 03:40 PM
  #7  
Supreme Member
 
Join Date: Mar 2008
Location: CT
Posts: 1,547
Likes: 0
Received 0 Likes on 0 Posts
Car: 86 T/A, 83 Z/28
Engine: 5.0 TPI, 350 2 X 4 bbl
Transmission: 4 speed auto, 5 speed manual
Axle/Gears: 3.23 posi, 3.73 std
Re: Rear Diffuser

Well if you wanted to do for appearance perposes you could make one from about any material you want. Ide use aluminum personally but thats just my preferance. Although for the functionality thats a whole differenct story. The theory about how aero dynamics works in relation to cars is air flow under the is not desiareable this explains the front air splitters and ground effects as a means to control air flow under the car. Now being that it is impossably to eliminate all air flow from under the car they actually try and use it to create vacuum under the car. How this is done is to simply have a small inlet of air in front under the car and increase this area under the car as the air travles further towards the back of the car. In effect assumeing that no air is allowed to leak in under the car from the sides you will have the same amount of air occupying a larger space. This creates a low pressure area pulling the car to the ground. Now on a race car this works great because they can have the ground effects just about touching the ground and they travle at very high speeds. Now in a pratical application on a steet car you cannot have ground effects close enought to the ground to give you adequit sealing to allow you to build up the low pressure. This is because air will be just sucked in from the sides of the car to balance the pressures. Now as you travel faster air may not be able to flow in fast enough to balance this pressure but on a street car you would have to go at extremly high speeds to achieve any noticable benifit and most cars arnt capeable of traveling that fast let alone take a turn which is where something like that would help most. Also as you may notice its not just a matter of a rear diffuser its the whole bottom of the car that must be reworked to achieve this effect. Just dont want you to go through all that work in hopes of getting some benifit your not going to get.
Rolling Thunder is offline  
Old 04-04-2009, 03:48 PM
  #8  
Member
Thread Starter
iTrader: (5)
 
strc09's Avatar
 
Join Date: Mar 2005
Location: Displaced Texan living in NC
Posts: 263
Likes: 0
Received 0 Likes on 0 Posts
Car: 1988 Pontiac Firebird Trans AM GTA
Engine: Tune-port Injected 6.3L
Transmission: Borg-Warner T56 six-speed
Axle/Gears: Borg/Warner 9-bolt with 3.70:1
Re: Rear Diffuser

If they're putting them on Mustangs (i.e. Cobras, Saleens) then they have to have some benefits and I'm sure the bottoms of those are not flat. I do understand that for this to get optimal effects the entire bottom would have to be sealed and smooth, but with the use of a front splitter and the rear diffuser there is surely some benefits because even at highway speeds they would be functioning (even if not to their absolute full potential).
strc09 is offline  
Old 04-04-2009, 03:59 PM
  #9  
Supreme Member
 
Join Date: Mar 2008
Location: CT
Posts: 1,547
Likes: 0
Received 0 Likes on 0 Posts
Car: 86 T/A, 83 Z/28
Engine: 5.0 TPI, 350 2 X 4 bbl
Transmission: 4 speed auto, 5 speed manual
Axle/Gears: 3.23 posi, 3.73 std
Re: Rear Diffuser

Well being that we dont have acess to something like a wind tunnel theres no way to really prove how much or at what speed you would need to be traveling to have a noticable effect. So really all this is just my oppnion/specualtion. Now i can say that you are right they are on cars like cobras, saleens ect but that dosnt mean it really has any effect per say. For example the newer camaro ss had a hood scoop that dosnt do anything eather. Ground effects many modern air foils although appearance wise appealing i dont believe they have much effect eather. So i think on a car like the mustangs its just to give it that race car look where as on a exotic sports car that can go 200 mph theres a bit more do it.
Rolling Thunder is offline  
Old 04-04-2009, 04:20 PM
  #10  
Member
Thread Starter
iTrader: (5)
 
strc09's Avatar
 
Join Date: Mar 2005
Location: Displaced Texan living in NC
Posts: 263
Likes: 0
Received 0 Likes on 0 Posts
Car: 1988 Pontiac Firebird Trans AM GTA
Engine: Tune-port Injected 6.3L
Transmission: Borg-Warner T56 six-speed
Axle/Gears: Borg/Warner 9-bolt with 3.70:1
Re: Rear Diffuser

I agree, but we could always scale model the wind tunnel.

Doing some research, my car for instance (Firebird) with the aero kit that was introduced in 1984 and carrying through 1990 had a drag coefficient of .32-ish (Firebird Trans AM ad) Since the objective is to get that number as close to zero as possible, again, I would imagine it would at least do something to help bring that number down by helping to create downforce which will lower the drag coefficiency number. That in turn would help achieve a higher top speed and could potentially aid in increased fuel economy because the car is now more "slippery" than before.

For now, attempting this is an idea. Since I can't find a manufacturer on-line anywhere that makes a diffuser four GenIII cars, it's something that more than likely is going to have to be fab'd up unless I can find something with similar demensions and modify it to fit on my car. I've never worked with fiberglass before so I really don't know how to make the mold and sculpt this into something that could potentially yeild promising results. That's not saying that I'm not willing to learn though. It would be even better if I could make this in carbon fiber so it was lighter.

After the reading and searching I've done today I do believe that this will provide some benefits even if it isn't utilized to its full potential as I mentioned previously. Also, I think it'd look killer and unique on the car.
strc09 is offline  
Old 04-04-2009, 04:55 PM
  #11  
Supreme Member
 
Join Date: Mar 2008
Location: CT
Posts: 1,547
Likes: 0
Received 0 Likes on 0 Posts
Car: 86 T/A, 83 Z/28
Engine: 5.0 TPI, 350 2 X 4 bbl
Transmission: 4 speed auto, 5 speed manual
Axle/Gears: 3.23 posi, 3.73 std
Re: Rear Diffuser

Well your free to try it if you like all im really trying to say is that theres no real proof that it will or will not help. Alot of people talk online about how things do this and that but cant back it up with any hard evidence. Some of its right some of its not but its good to have an open mind but be skeptical. I mean for all we know at this point it may create vacuum and suck air under the car actually hurting the drag coefficient or create more drag trying to straiten the air out than it reduces. All that being said though if you want to give it a shot thats fine its always nice to see people try new thing. Even if it dosnt work they way you hope we atleast learn from it. Keep in mind if you just want to reduce drag theres other things that can be done as well. Now getting to the real point as it seems your determined to give it a try i do work with fiberglass from time to time im no expert but i know the fundamentles of working with it and mold makeing. I actually learned alot of what i know from a guy that worked at a ferrari dealer makeing the custom molded seats (fabbed by hand molded to the customer and by spec had to weigh under 3 lbs!) and doing repairs on the composit bodies. I wouldnt recomend corbon fiber for 2 reasons. 1 its expencive and if your new to composites that could lead to a very expencive mistake and 2 to make carbon fiber come out and look nice with the pattern all strait and nice is also an art not really for a beginner honestly its out of my skill level as well on anything beond a virtually flat pannel. Personally i think it would be easyest to work from aluminum if you have a welder and some basic mettal working tools but i can help you if you want to learn to work with fiberglass and makeing molds and all that good stuff.
Rolling Thunder is offline  
Old 04-04-2009, 05:27 PM
  #12  
Member
Thread Starter
iTrader: (5)
 
strc09's Avatar
 
Join Date: Mar 2005
Location: Displaced Texan living in NC
Posts: 263
Likes: 0
Received 0 Likes on 0 Posts
Car: 1988 Pontiac Firebird Trans AM GTA
Engine: Tune-port Injected 6.3L
Transmission: Borg-Warner T56 six-speed
Axle/Gears: Borg/Warner 9-bolt with 3.70:1
Re: Rear Diffuser

The first part would be coming up with a design that works with the exhaust tips. I guess I'm going to have to build a model and see what it looks like and then figure out how to mock up a mini wind tunnel to see how it flows. For all I know...it could look hideous. Another thing to add to the long list of things I want to do. LOL! Splitter on the other hand already exists for GenIII cars. I found one of those on-line today as well as side splitters.

This is where I got the idea from...http://www.cardomain.com/ride/3013212
strc09 is offline  
Old 04-04-2009, 05:30 PM
  #13  
Junior Member
 
Join Date: Apr 2008
Location: Windsor, Ontario
Posts: 18
Likes: 0
Received 0 Likes on 0 Posts
Re: Rear Diffuser

Originally Posted by strc09 View Post
Since the objective is to get that number as close to zero as possible, again, I would imagine it would at least do something to help bring that number down by helping to create downforce which will lower the drag coefficiency number. That in turn would help achieve a higher top speed and could potentially aid in increased fuel economy because the car is now more "slippery" than before.
Just an FYI... the drag coefficient is based on the frontal area and velocity of the vehicle, so creating down force does not affect this number. However, increasing down force can increase your rolling resistance, which is technically not aero drag, but will create a resisting force opposite the direction of motion.

The whole idea behind diffusers is to reduce the size the wake behind the vehicle. This wake is an area of low pressure, and the larger its size the greater the pressure differential fore-aft along the vehicle. So by taking the high velocity air under the vehicle and diffusing it (or diverging it), you reduce its velocity and increase the pressure to prolong boundary layer separation and keep the wake a small as possible.
jacque_strap is offline  
Old 04-04-2009, 05:33 PM
  #14  
Member
Thread Starter
iTrader: (5)
 
strc09's Avatar
 
Join Date: Mar 2005
Location: Displaced Texan living in NC
Posts: 263
Likes: 0
Received 0 Likes on 0 Posts
Car: 1988 Pontiac Firebird Trans AM GTA
Engine: Tune-port Injected 6.3L
Transmission: Borg-Warner T56 six-speed
Axle/Gears: Borg/Warner 9-bolt with 3.70:1
Re: Rear Diffuser

Very good. Thanks for the additional info. I was looking for a diagram I found earlier, but can't find it again. Again thanks for the info.
strc09 is offline  
Old 04-04-2009, 05:36 PM
  #15  
Supreme Member
 
Join Date: Mar 2008
Location: CT
Posts: 1,547
Likes: 0
Received 0 Likes on 0 Posts
Car: 86 T/A, 83 Z/28
Engine: 5.0 TPI, 350 2 X 4 bbl
Transmission: 4 speed auto, 5 speed manual
Axle/Gears: 3.23 posi, 3.73 std
Re: Rear Diffuser

Originally Posted by jacque_strap View Post
Just an FYI... the drag coefficient is based on the frontal area and velocity of the vehicle, so creating down force does not affect this number. However, increasing down force can increase your rolling resistance, which is technically not aero drag, but will create a resisting force opposite the direction of motion.

The whole idea behind diffusers is to reduce the size the wake behind the vehicle. This wake is an area of low pressure, and the larger its size the greater the pressure differential fore-aft along the vehicle. So by taking the high velocity air under the vehicle and diffusing it (or diverging it), you reduce its velocity and increase the pressure to prolong boundary layer separation and keep the wake a small as possible.

Actually the drag coefficient is just a measure of how "slippery" something is. To figure out the actual amount of drag you need to account for the frontal area and the speed and dencity of the fluid its moving in ect but the drag coefficient itself is independent of all thoes factors.
Rolling Thunder is offline  
Old 04-04-2009, 05:38 PM
  #16  
Member
iTrader: (1)
 
RevItUpZ28's Avatar
 
Join Date: May 2003
Location: NC
Posts: 457
Likes: 0
Received 0 Likes on 0 Posts
Car: '91 Camaro Z28
Engine: 383 Vortec HSR
Transmission: Pro-Built 700-R4;Vig 4000 stall
Axle/Gears: Moser M9 9" / 3.89
Re: Rear Diffuser

You might want to check out this guys car.

It says on his site that his was custom made by carbon creations.
Attached Thumbnails Rear Diffuser-diffuser.jpg  
RevItUpZ28 is offline  
Old 04-04-2009, 05:40 PM
  #17  
Member
Thread Starter
iTrader: (5)
 
strc09's Avatar
 
Join Date: Mar 2005
Location: Displaced Texan living in NC
Posts: 263
Likes: 0
Received 0 Likes on 0 Posts
Car: 1988 Pontiac Firebird Trans AM GTA
Engine: Tune-port Injected 6.3L
Transmission: Borg-Warner T56 six-speed
Axle/Gears: Borg/Warner 9-bolt with 3.70:1
Re: Rear Diffuser

This is good...I'm still trying to learn all of this stuff. Found this while I was digging around today.

http://www.instructables.com/id/Meas...t-of-your-car/
strc09 is offline  
Old 04-04-2009, 05:42 PM
  #18  
Moderator
 
AlkyIROC's Avatar
 
Join Date: Jul 1999
Location: 51°N 114°W, 3500'
Posts: 16,738
Likes: 0
Received 3 Likes on 2 Posts
Car: 87 IROC L98
Engine: 588 Alcohol BBC
Transmission: Powerglide
Axle/Gears: Ford 9"/31 spline spool/4.86
Re: Rear Diffuser

Just how much downforce do you need? My car has the rear factory spoiler and at 140+ mph going through the traps, I still have enough downforce to keep the car going straight.

If you want to reduce turbulence under the car, use ground effects to make the body closer to the ground and fabricate a complete belly pan the full length of the car. I doubt you would see any benefits until you hit 180+ mph.

If you already have traction problems, more downforce isn't going to help.
AlkyIROC is online now  
Old 04-04-2009, 05:43 PM
  #19  
Member
Thread Starter
iTrader: (5)
 
strc09's Avatar
 
Join Date: Mar 2005
Location: Displaced Texan living in NC
Posts: 263
Likes: 0
Received 0 Likes on 0 Posts
Car: 1988 Pontiac Firebird Trans AM GTA
Engine: Tune-port Injected 6.3L
Transmission: Borg-Warner T56 six-speed
Axle/Gears: Borg/Warner 9-bolt with 3.70:1
Re: Rear Diffuser

Originally Posted by RevItUpZ28 View Post
You might want to check out this guys car.

It says on his site that his was custom made by carbon creations.
Sweet! Thanks. He is one of my CarDomain favorites and I didn't even notice it when I was looking through his page. This looks really nice.

strc09 is offline  
Old 04-04-2009, 05:45 PM
  #20  
Supreme Member
 
Join Date: Mar 2008
Location: CT
Posts: 1,547
Likes: 0
Received 0 Likes on 0 Posts
Car: 86 T/A, 83 Z/28
Engine: 5.0 TPI, 350 2 X 4 bbl
Transmission: 4 speed auto, 5 speed manual
Axle/Gears: 3.23 posi, 3.73 std
Re: Rear Diffuser

Originally Posted by strc09 View Post
The first part would be coming up with a design that works with the exhaust tips. I guess I'm going to have to build a model and see what it looks like and then figure out how to mock up a mini wind tunnel to see how it flows. For all I know...it could look hideous. Another thing to add to the long list of things I want to do. LOL! Splitter on the other hand already exists for GenIII cars. I found one of those on-line today as well as side splitters.

This is where I got the idea from...http://www.cardomain.com/ride/3013212

Yea idk if it would be worth while to try and build a mini wind tunnel as cool as it would be because alot of how it acts will be dependednt of it being on the car in a real world conditions. The only way to really test it would be to use like a 1:24 modle (which isnt a perfect 100% to begin with) of your car with a mini vertion of your design but even that rate it would be hard to make measurements of drag accurate enough to actually trust seeing as how your working small scale and little error will be multiplied out when working on the full scale. As far as makeing the modle if you have a good artist friend have them draw it for you. You can make a basic mock up from common materials like cardboard and expandable foam for example but even thats not as easy as having some one just draw u up a general idea.
Rolling Thunder is offline  
Old 04-04-2009, 05:48 PM
  #21  
Member
Thread Starter
iTrader: (5)
 
strc09's Avatar
 
Join Date: Mar 2005
Location: Displaced Texan living in NC
Posts: 263
Likes: 0
Received 0 Likes on 0 Posts
Car: 1988 Pontiac Firebird Trans AM GTA
Engine: Tune-port Injected 6.3L
Transmission: Borg-Warner T56 six-speed
Axle/Gears: Borg/Warner 9-bolt with 3.70:1
Re: Rear Diffuser

Originally Posted by Stephen 87 IROC View Post
Just how much downforce do you need? My car has the rear factory spoiler and at 140+ mph going through the traps, I still have enough downforce to keep the car going straight.

If you want to reduce turbulence under the car, use ground effects to make the body closer to the ground and fabricate a complete belly pan the full length of the car. I doubt you would see any benefits until you hit 180+ mph.

If you already have traction problems, more downforce isn't going to help.
I realize that this isn't going to reach its full potential, but I would imagine that it does provide some. Again, unless we put it in a wind tunnel we won't really know. Then again, I'm beginning to feel venturous about doing it by scale and making a model.

Thanks for all the input.
strc09 is offline  
Old 04-04-2009, 06:21 PM
  #22  
Junior Member
 
Join Date: Apr 2008
Location: Windsor, Ontario
Posts: 18
Likes: 0
Received 0 Likes on 0 Posts
Re: Rear Diffuser

Originally Posted by Rolling Thunder View Post
Actually the drag coefficient is just a measure of how "slippery" something is. To figure out the actual amount of drag you need to account for the frontal area and the speed and dencity of the fluid its moving in ect but the drag coefficient itself is independent of all thoes factors.
Actually, the coefficient of drag is a dimensionless parameter used to indicate an objects "streamline-ability" (if you will) and DOES depend on velocity, geometry and fluid density. This is because the Cd is a function of the Reynold's number, which in itself is a function of the aforementioned parameters. I'm not going to go into details - go read a fluid mechanics textbook if you don't believe me.
jacque_strap is offline  
Old 04-04-2009, 07:55 PM
  #23  
Member
Thread Starter
iTrader: (5)
 
strc09's Avatar
 
Join Date: Mar 2005
Location: Displaced Texan living in NC
Posts: 263
Likes: 0
Received 0 Likes on 0 Posts
Car: 1988 Pontiac Firebird Trans AM GTA
Engine: Tune-port Injected 6.3L
Transmission: Borg-Warner T56 six-speed
Axle/Gears: Borg/Warner 9-bolt with 3.70:1
Re: Rear Diffuser

Originally Posted by Rolling Thunder View Post
Yea idk if it would be worth while to try and build a mini wind tunnel as cool as it would be because alot of how it acts will be dependednt of it being on the car in a real world conditions. The only way to really test it would be to use like a 1:24 modle (which isnt a perfect 100% to begin with) of your car with a mini vertion of your design but even that rate it would be hard to make measurements of drag accurate enough to actually trust seeing as how your working small scale and little error will be multiplied out when working on the full scale. As far as makeing the modle if you have a good artist friend have them draw it for you. You can make a basic mock up from common materials like cardboard and expandable foam for example but even thats not as easy as having some one just draw u up a general idea.
I can handle the design part. It's a pretty simple design looking at it. It's just a matter of getting underneath the car adn taking measurments. I can do that when I get my car back from Charlotte. I wasn't really planning on getting into a full fledge science project with it since I'm not a math genius, but I did want to observe how the air would react as it passed over and under the car which can easily be done using a scale model. It's just a matter of finding a good high speed fan and something to make the air "visible" as it blows towards the model. That's the hard part and I'm definately open to suggestions. I was also thinking about getting some cardboard and trying to mock one up which is what I would use for my mold should I decide to go that route. Right now though, with the schedule I keep it's going to be a while before this all comes to fruition unless I get lucky and win the lottery. LOL!

Thanks again for the input and I'll continue reading up on how this stuff all works.
strc09 is offline  
Old 04-04-2009, 08:09 PM
  #24  
Junior Member
 
Join Date: Apr 2008
Location: Windsor, Ontario
Posts: 18
Likes: 0
Received 0 Likes on 0 Posts
Re: Rear Diffuser

If you do decide to make a scale model, you might be interested in looking up 'similarity coefficients' also known as dimensionless coefficients or parameters. This is a simple way of accurately scaling your model so things like size and wind speed will be proportionate. You would probably also want a flow straightener to eliminate the annular flow pattern of the fan and reduce turbulence in the model. Would be very cool to see.
jacque_strap is offline  
Old 04-04-2009, 10:03 PM
  #25  
Supreme Member
 
Join Date: Mar 2008
Location: CT
Posts: 1,547
Likes: 0
Received 0 Likes on 0 Posts
Car: 86 T/A, 83 Z/28
Engine: 5.0 TPI, 350 2 X 4 bbl
Transmission: 4 speed auto, 5 speed manual
Axle/Gears: 3.23 posi, 3.73 std
Re: Rear Diffuser

Typically what is done to make the air flow visable is to add some form of smoke. Now im not sure whats specifically is used to generate the smoke in a real wind tunnel but adding a controlled amount of smoke will make it visable. However i think more important would be to actually measure the forces acting on your diffuser as just because you see whats the airs doing it will be very hard to tell if its helping, hurting, or ne effect just on appearance. The other thing is im not sure weather your just planning on building and testing the diffuser on its own or as part of a actual modle of your car but it would be hard to tell its effects if your just testing the diffuser itself it would really need to be based on some model of your car.
Rolling Thunder is offline  
Old 04-05-2009, 06:38 AM
  #26  
Member
Thread Starter
iTrader: (5)
 
strc09's Avatar
 
Join Date: Mar 2005
Location: Displaced Texan living in NC
Posts: 263
Likes: 0
Received 0 Likes on 0 Posts
Car: 1988 Pontiac Firebird Trans AM GTA
Engine: Tune-port Injected 6.3L
Transmission: Borg-Warner T56 six-speed
Axle/Gears: Borg/Warner 9-bolt with 3.70:1
Re: Rear Diffuser

A very simple way to tell if the diffuser is having any effect is to put the model in without the part and see how the air reacts as it exits the car from underneath the rear. Once that is observed you can then add the part and observe whether there is a difference in the way the air exits. Depending on whether the air is smoothed out or less turbulent than when running the model without the part would tell whether there is any benefit from having it or not. Since I don't have the math or engineering background to figure out every small detail it's more of a test to see if it even works. I think just being able to observe the wind patterns will give an idea of whether it will work or not. If there is no visible difference in the wind pattern from the model without the diffuser to when you repeat the test with model using the diffuser then there is no benefit. On the flipside to that should you see a difference in air patterns then it's worth a shot to move on to full-scale testing. I see this as a win/win here. One, I learn something new (proving you can still teach old dogs new tricks) and playing around with some cool science projects that I can do with me kids. Then two, it makes for a unique appearance mod that isn't very common on our cars.
strc09 is offline  
Old 04-05-2009, 10:27 AM
  #27  
Supreme Member
 
Join Date: Mar 2008
Location: CT
Posts: 1,547
Likes: 0
Received 0 Likes on 0 Posts
Car: 86 T/A, 83 Z/28
Engine: 5.0 TPI, 350 2 X 4 bbl
Transmission: 4 speed auto, 5 speed manual
Axle/Gears: 3.23 posi, 3.73 std
Re: Rear Diffuser

Well absolitly we dont have the equipment neccessary to make yeil results with any kind of accuracy so theres really not much point in treating it that way. Hopefully it will end up like your saying a better or worse kinda thing rather than a measure of how much effect. The only thing i think is maby you could set up a scale to measure the amount of drag. Wouldnt have to be overly complicated just a light weight scale that would measure the amount of pull the car generates in the wind tunnle. Obvioulsy if the pull decreases with your design the aero dynamics of the car have been improved. The only reason i wonder this is just because the air was straitened who knows if that actually resulted in a net drop of aero dynamic drag. I mean it may cause more drag straitening the air than it reduced.
Rolling Thunder is offline  
Old 04-05-2009, 04:53 PM
  #28  
Supreme Member
iTrader: (2)
 
83 Crossfire TA's Avatar
 
Join Date: Jun 2001
Location: DC Metro Area
Posts: 7,660
Likes: 0
Received 0 Likes on 0 Posts
Car: 87TA 87Form 71Mach1 12SHO 04Cummins
Re: Rear Diffuser

Some of this conversation is truly painful, and it’s funny, because some of you have shown that you should have some clue with discussions of Cd and Reynolds numbers…

1- As has been noted, just because a mustang might come with one, doesn’t mean it works or does anything useful at a usable speed. Much of what you see people putting on cars isn’t useful on the street or even near street speeds, and even if it is, isn’t useful for street driving. The fact is that most of what you see on even really fast street cars only amounts to styling, and as far as performance only really adds up to extra weight and drag. But it looks cool.
2- Cd * frontal area determines drag. Cd is roughly determined by the shape of the vehicle. You have to keep BOTH Cd down and frontal area to lower aerodynamic drag.
3- Most firebirds have a Cd around .32, some of the early Trans Ams with the right aero package and trim got as low as .28. I believe that most camaros had Cd’s in the .32-.34 range
4- Almost anything that manipulates airflow to generate lift (downforce is just lift pushing downward), will increase Cd and usually frontal area significantly, greatly increasing drag. You don’t see diffusers, spoilers (which do just what their name suggests, spoils smooth airflow), splitters… on dedicated land speed cars or something intended for efficiency/mpg, unless they are so unstable without them that there is no choice. You also don’t see the kinds of things that you usually see with the winged cars, like fat tires… all of which increase frontal area.
5- Crawl under an f-body and take a good hard look, there is factory sheet metal that is intended to do some of what you’re talking about under there, and making it more prominent/functional is going to be _very_ difficult without making something that will actually act as a bit of a parachute, doing nothing but creating drag.
6- Scale models in a wind tunnel don’t do much for something like this, where you’re trying to see the effects of smaller changes. They are good at showing macro, whole system changes, but you won’t easily see the difference that say a ½” lower front air dam would make or a slight change in a rear wings angle or diffuser design.
7- Yes, you can test all this without a wind tunnel, if you have a good concept of laminar vs turbulent airflow, separation, boundary layer and surface aerodynamics… Attach tufts of yarn or streamers to the vehicle and follow it or even better, have someone video tape it from different angles as it’s driven. These will give you a very good idea of what airflow is doing when it goes over and past the surface of your vehicle. If you can figure out how to rig a ride height transducer (lots of ways to do this, you can even do a very simple mechanical setup like a rubber washer on a shock rod if you have a very smooth surface to test on), you can figure out relative downforce, or even estimate actual downforce if you can figure out the wheel rate of your suspension

Basically, don’t fool yourself into thinking that you’ve got all this aero crap and your car is going to be more slippery and faster…. If you want it to be as fast and efficient as possible it will be teardrop shaped. Any angle of attack, deviation from the shape, or any bit of aerodynamic garbage stuck to that shape will slow you down/hurt efficiency. Generally, because of the envelope that we force cars to work in, and what we try to package in a car body, the most aerodynamic shape that you can get away with IRL will have significant lift.

Secondly, unless you mount MASSIVE wings and deal with the resultant massive drag, you’re not going to generate enough down force at any speed you’re likely to see in anything resembling a street car. Look at the wings, and other good stuff on indy and formula cars, and then consider the speeds that they run at and how largely irrelevant they become at tight road course speeds. Yes they do something at 150mph… I’d bet that most of the people in this conversation haven’t been at 150mph before, and those that have could probably count the number of times on one hand.
83 Crossfire TA is offline  
Old 04-06-2009, 09:29 AM
  #29  
Member
Thread Starter
iTrader: (5)
 
strc09's Avatar
 
Join Date: Mar 2005
Location: Displaced Texan living in NC
Posts: 263
Likes: 0
Received 0 Likes on 0 Posts
Car: 1988 Pontiac Firebird Trans AM GTA
Engine: Tune-port Injected 6.3L
Transmission: Borg-Warner T56 six-speed
Axle/Gears: Borg/Warner 9-bolt with 3.70:1
Re: Rear Diffuser

Thanks for the input.

I've never said that I knew everything there is to know about this stuff. I don't have a degree in aerodynamic engineering, how many aerodynamic engineers do we really have here on TGO? So, for many of us...I think this thread would be considered hypothetical and theory based on what "we" non-aerodynamic engineers possess knowledge wise. With that said, this is the first time I've really given aerodynamics any serious thought. Also, I didn't just blindly post this thread without doing a little bit of reading before hand finding out what this part is and how it is supposed to function. From what I read a rear diffuser seems like a good idea with some benefits that could even possibly be observed in street cars at highway speeds.

I am aware of how well our cars were aerodynamically for their time. That was definately one of their finer attributes. Also, since I own a Firebird I have a wing and not a spoiler like my Camaro bretheren. I've read the design of the aerowing is actually a very good design which actually functions like it is supposed to. As for the underside of my car, what exactly am I supposed to be looking for that is designed to act in this capacity? IF any of our cars were already designed with some of these qualities then what gives you the impression this could hurt/hinder the airflow instead of enhance it? Do you have any specific examples for me to observe the next time I'm under my car? Again, as for the diffuser I believe the idea is to smooth out the turbulent air as it exits the car from the underside. Since the undercarriage isn't completely smooth the diffuser helps return that air to a more smooth manner as it joins the air coming over the top of the car as I understand what I've read. In addition, the strakes on the diffuser help to channel that air providing additional air stability as it exits the rear of the car and joining with the air flowing over the top.

As for the scale model, it isn't meant to provide the difinitive answers to whether this will work or not. It is more to study the viability of whether it actually works or not on our type of cars. Simply observing the airflow should give you an idea of whether it works or not. Again, If you take a regular model and observe the airflow you should be able to track how it flows over the model visually. Change the model and again, you should be able to track how the air flows have changed over the model in correspondence with the changes you made. Very simple and will show if the addition of aerodynamic parts (i.e. diffusers, splitters, canards, etc.) have any effect. 100% acurate, probably not unless you made an exact scale model of everything then ran all sorts of tests and ran formulas etcetera. That's not the focus though. While it'd be nice for the results to be as accurate as possible, the point is observe airflow which as long as the model and the parts are to scale then that should be sufficient to do just that...observe airflow just as they do in wind tunnels on actual cars.

Now, I like your idea about the yarn and definately solves part of the problem of how to observe airflow in the model. I hadn't thought about taping yarn to the actual car though, but is definately a good idea which I'll give some consideration to should I actually decide to pursue this. Right now I still haven't decided yet since this is more than likely going to have to be something that is custom made. Right now, this thread is meant as more of a plan/study phase and to share any specs that someone who might have already tried something like this to share. Does it work, does it not, does it affect how the car handles, etc.

So, since ALL of us here at TGO are aerodynamic engineers for a living then we all have an EXPERT knowledge of what's going on here. I highly doubt that and at most the conclusions any of us can make our decisions on are articles written on the subject posted elsewhere on the internet or as I mentioned through your own personal experiences. Now, just because I did some reading up on how this part is supposed to work and some theories behind automotive aerodynamics does it make me an authority...nope...not in the least bit just as I don't believe it makes anyone else who posts in this thread unless you are a professional aerodynamic engineer, physicist, mathmetician, or whatever fancy degrees you need to make a fully educated post on the subject. Regardless of how "painful" or "funny" it may be percieved that parts of this conversation are, no one is an expert and assuming that anyone is based on what they post isn't responsible either. Most people post based on information they read from other sources and have no practical experience. I've made it clear in my previous posts that I'm learning something new. Disparaging comments because you don't agree really aren't neccessary since I'm sure that none of us here are experts and only have a limited knowledge on how any of this stuff works.

Again, thanks for the input.
strc09 is offline  
Old 04-06-2009, 09:31 AM
  #30  
Supreme Member
 
paul_huryk's Avatar
 
Join Date: Jul 1999
Location: Ahead of you...
Posts: 2,744
Likes: 0
Received 0 Likes on 0 Posts
Car: 1984 LG4 Camaro
Engine: 350 Roller Motor
Transmission: Level 10 700R4
Axle/Gears: Strange 12 bolt 3.42
Re: Rear Diffuser

Originally Posted by 83 Crossfire TA View Post
Some of this conversation is truly painful, and it’s funny, because some of you have shown that you should have some clue with discussions of Cd and Reynolds numbers…

1- As has been noted, just because a mustang might come with one, doesn’t mean it works or does anything useful at a usable speed. Much of what you see people putting on cars isn’t useful on the street or even near street speeds, and even if it is, isn’t useful for street driving. The fact is that most of what you see on even really fast street cars only amounts to styling, and as far as performance only really adds up to extra weight and drag. But it looks cool.
2- Cd * frontal area determines drag. Cd is roughly determined by the shape of the vehicle. You have to keep BOTH Cd down and frontal area to lower aerodynamic drag.
3- Most firebirds have a Cd around .32, some of the early Trans Ams with the right aero package and trim got as low as .28. I believe that most camaros had Cd’s in the .32-.34 range
4- Almost anything that manipulates airflow to generate lift (downforce is just lift pushing downward), will increase Cd and usually frontal area significantly, greatly increasing drag. You don’t see diffusers, spoilers (which do just what their name suggests, spoils smooth airflow), splitters… on dedicated land speed cars or something intended for efficiency/mpg, unless they are so unstable without them that there is no choice. You also don’t see the kinds of things that you usually see with the winged cars, like fat tires… all of which increase frontal area.
5- Crawl under an f-body and take a good hard look, there is factory sheet metal that is intended to do some of what you’re talking about under there, and making it more prominent/functional is going to be _very_ difficult without making something that will actually act as a bit of a parachute, doing nothing but creating drag.
6- Scale models in a wind tunnel don’t do much for something like this, where you’re trying to see the effects of smaller changes. They are good at showing macro, whole system changes, but you won’t easily see the difference that say a ½” lower front air dam would make or a slight change in a rear wings angle or diffuser design.
7- Yes, you can test all this without a wind tunnel, if you have a good concept of laminar vs turbulent airflow, separation, boundary layer and surface aerodynamics… Attach tufts of yarn or streamers to the vehicle and follow it or even better, have someone video tape it from different angles as it’s driven. These will give you a very good idea of what airflow is doing when it goes over and past the surface of your vehicle. If you can figure out how to rig a ride height transducer (lots of ways to do this, you can even do a very simple mechanical setup like a rubber washer on a shock rod if you have a very smooth surface to test on), you can figure out relative downforce, or even estimate actual downforce if you can figure out the wheel rate of your suspension

Basically, don’t fool yourself into thinking that you’ve got all this aero crap and your car is going to be more slippery and faster…. If you want it to be as fast and efficient as possible it will be teardrop shaped. Any angle of attack, deviation from the shape, or any bit of aerodynamic garbage stuck to that shape will slow you down/hurt efficiency. Generally, because of the envelope that we force cars to work in, and what we try to package in a car body, the most aerodynamic shape that you can get away with IRL will have significant lift.

Secondly, unless you mount MASSIVE wings and deal with the resultant massive drag, you’re not going to generate enough down force at any speed you’re likely to see in anything resembling a street car. Look at the wings, and other good stuff on indy and formula cars, and then consider the speeds that they run at and how largely irrelevant they become at tight road course speeds. Yes they do something at 150mph… I’d bet that most of the people in this conversation haven’t been at 150mph before, and those that have could probably count the number of times on one hand.
I'm going to add some stuff to crossfire's good post...

1) Agreed - all street "aero kits" are meant to give the car a look of agression or slickness and may in fact make the aerodynamics worse.

2) You can do things to lower a car's Cd, but frontal area is very hard to make smaller in a street application.

3) While the aero of the thirdgens in general is still excellent, even for today, I think GM could have done more.

4) True - most top speed cars leave stock body pieces on for their runs. But the problem is they add extra weight into the cars to keep them on the road. Weight is the #1 enemy of tires at ultra high speeds as they can ans will overheat and fail. Weight is a band aid for some aero tricks that these cars should have.

5) This is my biggest problem with GM and their lack of aero insight - the underbody of their cars. Starting from the front of a third gen (or fourthgen), the air is banged around into the radiator with a air dam, hits exhaust pipes, rearend, and tires before it exits out the back of the car. Lots of drag is created and even the cooling system is taxed as the airflow is 100% wrong. This is the area of most improvement for the GM cars.

6) Scale models only tell 1/2 the story...

7) Wind tunnel is a tool, but it does tell you a lot about what is going on.

Downforce is generated through the car's shape and aero treatments (splitters, spoilers, wings). Formula 1 and Indy cars generate a lot of downforce at low speeds (even at 60mph) due to their optimization of the body shape, wings, and other technology. The reason is that the rules say open wheel (a huge drag generator) and with that, the quickest way around a track is to maximize downforce even with the massive drag penalty. There was a test back in the 80's where they pitted an INDY car against a NASCAR racer... The Indycar weighed 1/2 of the NASCAR, had similar power, and had a much smaller frontal area yet went 20mph less in top speed due to the high drag wing design of the car. Lesson learned.

There is a huge window for improvement...
paul_huryk is offline  
Old 04-06-2009, 11:21 AM
  #31  
Supreme Member
 
Join Date: Mar 2008
Location: CT
Posts: 1,547
Likes: 0
Received 0 Likes on 0 Posts
Car: 86 T/A, 83 Z/28
Engine: 5.0 TPI, 350 2 X 4 bbl
Transmission: 4 speed auto, 5 speed manual
Axle/Gears: 3.23 posi, 3.73 std
Re: Rear Diffuser

Like i always say keep an open mind while remaining skeptical. Now personally im curious about whats so "painful" about this discussion? Because none of us have any real hard evidence weather this idea will or will not work you cannot blindly say that it will not and thats what has led into this long disscussion. Even though i am fairly confident that adding a diffuser of this design wont have any advantage i have no evidence back up that statement other than "something of that nature wont help untill your moveing at speeds outside of the limits of most cars" or "the mustangs use of a diffuser is probably just for apperance" or "the drag generated by trying to straiten out the air may be more than it reduces." Neither of thoes statments have any actual hard facts there just speculation based on looking at other examples of this technology being used. Because i realize i cannot diffinitvly prove that this will not work means i have to accept the possability it may. The fact that the original poster is approaching this idea to a somewhat scientific manner to verify his results of weather this will help or not is something that should be noted and respected.
Rolling Thunder is offline  
Old 11-15-2011, 10:16 PM
  #32  
Member
 
ChevyRS-305's Avatar
 
Join Date: Mar 2006
Location: Ellis Grove Il
Posts: 445
Likes: 0
Received 0 Likes on 0 Posts
Car: 1989 Camaro RS/ 1992 Camaro z28
Engine: 383 Stroker/ ls3 e-rod
Transmission: borge warner t-56/ tremech t-56
Axle/Gears: 10 bolt, 3.55/ dayna 44(viper) 3.07
Re: Rear Diffuser

Originally Posted by strc09 View Post
Sweet! Thanks. He is one of my CarDomain favorites and I didn't even notice it when I was looking through his page. This looks really nice.

Yea this guy has an account on here. He goes by NufNuffZ28 that rear diffuser was not made by carbon-creations but yet the "fins" where purchased through extreme dimensions and he made the rest from tin and angle iron.
Attached Thumbnails Rear Diffuser-img01610.jpg   Rear Diffuser-img01612.jpg  
ChevyRS-305 is offline  
Old 11-17-2011, 05:16 PM
  #33  
Junior Member
iTrader: (3)
 
Join Date: Aug 2008
Location: the big ol nc
Posts: 60
Likes: 0
Received 0 Likes on 0 Posts
Car: 88 t/a tpi ported polished bolt ons
Engine: lb9 got 406 on paymnt wow FI 406
Transmission: 700r4
Axle/Gears: 99 z28 342 in back
Re: Rear Diffuser

TIP TERR ALSO HAS A DIFUSER
dirtybrd88 is offline  
Old 11-17-2011, 06:44 PM
  #34  
Member
 
ChevyRS-305's Avatar
 
Join Date: Mar 2006
Location: Ellis Grove Il
Posts: 445
Likes: 0
Received 0 Likes on 0 Posts
Car: 1989 Camaro RS/ 1992 Camaro z28
Engine: 383 Stroker/ ls3 e-rod
Transmission: borge warner t-56/ tremech t-56
Axle/Gears: 10 bolt, 3.55/ dayna 44(viper) 3.07
Re: Rear Diffuser

Whats the website for that?
ChevyRS-305 is offline  
Old 11-18-2011, 07:56 PM
  #35  
Junior Member
iTrader: (2)
 
mattyc's Avatar
 
Join Date: Nov 2008
Location: manchester, NH
Posts: 63
Likes: 0
Received 0 Likes on 0 Posts
Car: 1998 grand cherokee, 1988 iroc z
Engine: 350 tpi
Transmission: 700r4
Axle/Gears: ???
Re: Rear Diffuser

they look like cow udders
mattyc is offline  
Old 11-18-2011, 08:06 PM
  #36  
Supreme Member
iTrader: (5)
 
Thirdgen89GTA's Avatar
 
Join Date: Sep 2004
Location: Chicagoland Suburbs
Posts: 5,165
Likes: 0
Received 0 Likes on 0 Posts
Car: 1989 Trans Am GTA
Engine: LT1, AFR 195cc, 231/239 LE cam.
Transmission: M28 T56
Axle/Gears: 3.23 10bolt waiting to explode.
Re: Rear Diffuser

Originally Posted by mattyc View Post
they look like cow udders
If its built right it smooths the transition for airflow coming from underneath the car which decreases lift at the rear, as well as decreasing drag. Which is a double bonus because most times a spoiler or wing will increase downforce at the expense of drag.

Any time you can clean up the air under a car its a double bonus.

Last edited by Thirdgen89GTA; 11-18-2011 at 08:10 PM.
Thirdgen89GTA is offline  
Old 11-18-2011, 08:12 PM
  #37  
Supreme Member
 
ASE doc's Avatar
 
Join Date: Apr 2010
Location: Aurora, OR
Posts: 4,230
Likes: 0
Received 0 Likes on 0 Posts
Car: 87 IROC Z28
Engine: 355 cid TPI
Transmission: Pro Built Auto 700R4 w/3,500 stall
Axle/Gears: QP fab 9" 3.70 Truetrac
Re: Rear Diffuser

Looks kind of silly to me and I can't imagine it really improves one of the most aerodynamic bodies ever built. If you look back over the worlds fastest stock bodied cars, you'll find that the #1 is a 92 Firebird(304mph, no body modifications at all). Another was an 88 IROCZ(287MPH totally stock body). There is little to be done to these cars that will improve their aerodynamics. But if you think that thing looks good, suit yourself.
ASE doc is offline  
Old 11-18-2011, 08:39 PM
  #38  
Supreme Member
iTrader: (5)
 
Thirdgen89GTA's Avatar
 
Join Date: Sep 2004
Location: Chicagoland Suburbs
Posts: 5,165
Likes: 0
Received 0 Likes on 0 Posts
Car: 1989 Trans Am GTA
Engine: LT1, AFR 195cc, 231/239 LE cam.
Transmission: M28 T56
Axle/Gears: 3.23 10bolt waiting to explode.
Re: Rear Diffuser

Originally Posted by ASE doc View Post
Looks kind of silly to me and I can't imagine it really improves one of the most aerodynamic bodies ever built. If you look back over the worlds fastest stock bodied cars, you'll find that the #1 is a 92 Firebird(304mph, no body modifications at all). Another was an 88 IROCZ(287MPH totally stock body). There is little to be done to these cars that will improve their aerodynamics. But if you think that thing looks good, suit yourself.
I believe I have the 304mph article somewhere in High Performance Pontiac and there was work on the underbody that significantly reduced lift/drag at speed by controlling airflow underneath the car.

I have the article at work, I will scan it once I get back from vacation.
Thirdgen89GTA is offline  
Old 11-18-2011, 08:41 PM
  #39  
Supreme Member
iTrader: (7)
 
TTOP350's Avatar
 
Join Date: Oct 2001
Location: central Il USA
Posts: 10,171
Received 8 Likes on 6 Posts
Car: 1989-92 FORMULA350 305 92 Hawkclone
Engine: 4++,350 & 305 CIs
Transmission: 700R4 4800 vig 18th700R4 t56 ZF6 T5
Axle/Gears: 3.70 9"ford alum chunk,dana44,9bolt
Re: Rear Diffuser

The 300 mph firebird started out as a 88 I think. It has quite a few tweeks to the aero stuff. Thats what Jim Mattison told me.

I have worked on several Ford GTs. If you didnt know what the bottom looks like its super flat with vortex generators all over it. It looks like a unwrapped golf ball laid flat.
Here is a link to enhanced aftermarket Ford GT parts.

http://www.gtc-mirage.com/MIRAGE/mir...o-package.html

Last edited by TTOP350; 11-18-2011 at 08:45 PM.
TTOP350 is online now  
Old 11-18-2011, 10:32 PM
  #40  
Senior Member
 
89_RS's Avatar
 
Join Date: Jul 2008
Location: Ft Wayne, IN
Posts: 808
Likes: 0
Received 0 Likes on 0 Posts
Car: 2003 F-150
Engine: 4.6L Modular V8
Transmission: 4R70W
Axle/Gears: Ford 8.8"/3.55 LSD
Re: Rear Diffuser

The problem isn't that the part doesn't work, it does. However; its not effective by itself. When we put the aero package on the 2010 Purdue FSAE car the data showed that it would only be worth it if we did the whole thing: front & rear wings, side pods, underbody & diffuser trays, front air splitter, and nose cone. Now, thats not to say you won't get a return from the diffuser, but you would be wise to consider making an underbody tray & front air splitter. RIT did this on there 2009 FSAE car and had one of the lightest & fastest cars on the track because of it. Those 3 items together get you the most bang for the buck.

Know any Aeronautical Engineers working on car aero packages on the cheap?
89_RS is offline  
Old 11-20-2011, 12:08 PM
  #41  
Member
 
ChevyRS-305's Avatar
 
Join Date: Mar 2006
Location: Ellis Grove Il
Posts: 445
Likes: 0
Received 0 Likes on 0 Posts
Car: 1989 Camaro RS/ 1992 Camaro z28
Engine: 383 Stroker/ ls3 e-rod
Transmission: borge warner t-56/ tremech t-56
Axle/Gears: 10 bolt, 3.55/ dayna 44(viper) 3.07
Re: Rear Diffuser

Here are some cool carbon fiber websites that will fully set you up with aerodinamics.

http://aprperformance.com/

http://extremedimensions.com/

http://www.dragonplate.com/default.asp

www.rjracecars.com

http://www.grace-co.co.jp/product.html

http://www.carbonmods.co.uk/Default.aspx

And if you want to make your own stuff from scratch just play around on this site for a day.... http://www.fibreglast.com/

Last edited by ChevyRS-305; 11-20-2011 at 12:19 PM.
ChevyRS-305 is offline  
Old 11-21-2011, 03:16 PM
  #42  
Supreme Member
 
ASE doc's Avatar
 
Join Date: Apr 2010
Location: Aurora, OR
Posts: 4,230
Likes: 0
Received 0 Likes on 0 Posts
Car: 87 IROC Z28
Engine: 355 cid TPI
Transmission: Pro Built Auto 700R4 w/3,500 stall
Axle/Gears: QP fab 9" 3.70 Truetrac
Re: Rear Diffuser

Originally Posted by TTOP350 View Post
The 300 mph firebird started out as a 88 I think. It has quite a few tweeks to the aero stuff. Thats what Jim Mattison told me.

Google "Kugel Racing" and find the 92 Firebird on their website. They have a nice video clip of the 304mph run. The top speed car was a completely stock bodied 92 Trans Am. Of course it was running a 1,400HP twin turbo small block. The Stock Body top speed competition prohibits body modifications that may affect aerodynamics. The car had Ferrari air intake ducts on the hood for the turbo inlets and it was lowered 3". That's it. The 287 mph 88IROC I referred to was also a stock body car. It used the Trans Am rear spoiler, which is allowed because it is a factory part for the Fbody. It was power by an 850HP carbureted 358cid small block with a crazy intake air cooler that the owners had created. These cars were both running 10+ years ago.
ASE doc is offline  
Old 11-21-2011, 03:55 PM
  #43  
Supreme Member
iTrader: (7)
 
TTOP350's Avatar
 
Join Date: Oct 2001
Location: central Il USA
Posts: 10,171
Received 8 Likes on 6 Posts
Car: 1989-92 FORMULA350 305 92 Hawkclone
Engine: 4++,350 & 305 CIs
Transmission: 700R4 4800 vig 18th700R4 t56 ZF6 T5
Axle/Gears: 3.70 9"ford alum chunk,dana44,9bolt
Re: Rear Diffuser

Gale Banks had a 86 TA (268mph)that morfed into a 87 (283mph)and 88 GTA. I "think" Uncle John Lingenfelter ended up with the car and went 298mph.
This is from Lingenfelters web site.
In 1989, John moved on to help set another record, this time at the Bonneville Salt Flats. Lingenfelter built a 355 CID Chevy V8 engine for the SE Racecraft 1989 Firebird Trans Am. This twin-turbocharged, fuel- injected small block produced 1,400 hp and had six nitrous bottles for intercooler cooling only, not for induction. The car’s driver, Gary Eaker, tried to break the 300 mph barrier in the Trans Am but after several attempts fell short of the goal. He did, however, still hit an amazing 298 mph, which set the record for full-body sedans at the time.

Then it went to Kugel or a body in white? They stripped the car?,updated the bodywork? and they did the 300mph boogie with the car..
The reason I believe this story is if you look at a pic of the Kugel car it has a 84 dash, 85 taillights and unpainted black rear wing. A old pontiac test car of some kind? 92 body in white with junk yard parts?? who knows!?
http://www.hotrod.com/featuredvehicl.../photo_02.html

Was there 1-2-3-4-5 cars ?? I'm not sure. Thought I read this before.
Ive been looking at pix and it looks like
Banks has a fabbed wing and stock unpainted wing in diff pix
John L has 91-2 body work on his car with a painted wing.
Kugel has 91-2 an unpainted wing and 85 tails

Last edited by TTOP350; 11-21-2011 at 05:18 PM.
TTOP350 is online now  
Old 11-26-2011, 11:04 AM
  #44  
Supreme Member
 
Join Date: Dec 2002
Location: Central FL
Posts: 2,562
Likes: 0
Received 0 Likes on 0 Posts
Car: 91 Camaro
Engine: 3.1...not hardly stock
Transmission: 700r4....not stock either
Axle/Gears: 3.73
Re: Rear Diffuser

Ive thought about building a full belly pan with a rear diffuser. The issues I thought of that was part of what kept me from doing it was heat and air flow. The air that comes in the grille, through the radiator has to go somewhere...if you're going to do a full pan underneath...keep this in mind. Also, exhaust heat. depending on how you vent the air out from the radiator, you may be trapping exhaust heat under the car which may well translate into the inside of the car. And, I had a hard time deciding how I'd work around the muffle if it were to be kept in its stock location.
AM91Camaro_RS is offline  
Old 12-05-2011, 10:54 PM
  #45  
Supreme Member
 
tylercamaro's Avatar
 
Join Date: Aug 2009
Location: Clinton Township, Michigan
Posts: 2,037
Likes: 0
Received 0 Likes on 0 Posts
Car: 92 Trans Am GTA
Engine: 305
Transmission: 700r4
Axle/Gears: 2.73
Re: Rear Diffuser

i say go on 6litre eater, buy a ceta panel with diffuser for a 98-02 and graft it into yours then run the exhuast through it as well
tylercamaro is offline  
Old 12-06-2011, 02:12 AM
  #46  
Supreme Member
iTrader: (4)
 
Join Date: Dec 2005
Location: Macon, GA
Posts: 6,476
Likes: 0
Received 0 Likes on 0 Posts
Car: 1992 Camaro RS
Engine: Vortec headed 355, xe262
Transmission: T56
Axle/Gears: 9-bolt 3.70
Re: Rear Diffuser

Probably has been mentioned, but a diffuser is a waste of time and energy without a belly pan, a front splitter, and an extremely low ride height to maximize the ground effect, and by low, I mean less than an inch.

If you want downforce, get a wing.

Here are some known effective ones:

http://www.blainefabrication.com/spoiler.html

http://fulcrumaero.com/

Last edited by InfernalVortex; 12-06-2011 at 02:20 AM.
InfernalVortex is offline  
Old 12-10-2013, 10:46 AM
  #47  
Member
 
Join Date: Mar 2013
Location: Tennessee
Posts: 264
Likes: 0
Received 0 Likes on 0 Posts
Car: 92 camaro
Engine: 5.7l 350
Transmission: t5
Axle/Gears: 2.73
Re: Rear Diffuser

awesome
rfoster23g is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
Vintageracer
Camaros for Sale
10
05-15-2019 12:02 AM
1992 Trans Am
History / Originality
22
02-03-2019 04:10 AM
hectre13
Engine/Drivetrain/Suspension Parts for Sale
1
12-27-2015 08:30 PM
Bstrang6
Brakes
2
08-24-2015 06:45 AM
customblackbird
Suspension and Chassis
0
08-10-2015 09:30 AM


Thread Tools
Search this Thread
Quick Reply: Rear Diffuser


Contact Us - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: