how functional is a rear diffuser like this?
Insane Burnout
Joined: Oct 2003
Posts: 1,568
Likes: 0
From: Pleasanton, CA
i also do agree that there are diffusers that are completely functional, i was just saying that i dont think that the "old school" RE A diffuser in the picture isn't that functional.
I do wonder though if any of these diffusers are functional in the slightest. You would think big company's like Mazdaspeed and RE Amemiya spend time wind tunnel and on-road testing of the diffusers, so they must help some, even though it might not be alot. You never know.
I do wonder though if any of these diffusers are functional in the slightest. You would think big company's like Mazdaspeed and RE Amemiya spend time wind tunnel and on-road testing of the diffusers, so they must help some, even though it might not be alot. You never know.
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Full Member
Joined: Mar 2001
Posts: 213
Likes: 0
From: Charleston, WV, USA
Words mean things.
"Functional" is a generous term and cannot accurately be used to determine the worth of an item.
"Functional illiterate" is how school systems try to categorize someone that has been shuffled through the system, has been given passing grades and is generally liked by everyone. The sad thing is they can't read and write.
A 15 watt dome light bulb is functional as a headlight. It will illuminate the front of the car. Just because it is functional, it doesn't mean it functions in the job it is being used for.
First, believe no claims from any vendor. These people are merely trying to sell their bits and pieces. Sure, some of the Japanese stuff is used on their race cars, but that doesn't make them any more legitimate.
Second, sure some of these items are probably "wind tunnel tested" but what difference does that make. So what if they could hang something off the rear of the car and be able to detect a change in the airflow. You can also hold your hand out the window and increase downforce.
I guarantee that when any of these items are used on real racing cars they are properly loaded with belly pans that extend to the center of pressure. Additionally, the diffusers on race cars are used at a much lower ride height.
Check out the diffuser on the Oreca Vipers. It runs 4 feet under the car and its blades are barely a hand thickness off the ground.
The point is that nobody is going to get ANY benefit from running one of these decorative items on their street car. Track guys may or may not want additional aerodynamic items on their cars. I have friends that have removed wings, splitters and other things as they learn how their car handles at high speed.
If you like how these diffusers look (and I do think some of them look neat), fine, quit lying to yourself believing that they perform anything whatsoever.
"Functional" is a generous term and cannot accurately be used to determine the worth of an item.
"Functional illiterate" is how school systems try to categorize someone that has been shuffled through the system, has been given passing grades and is generally liked by everyone. The sad thing is they can't read and write.
A 15 watt dome light bulb is functional as a headlight. It will illuminate the front of the car. Just because it is functional, it doesn't mean it functions in the job it is being used for.
First, believe no claims from any vendor. These people are merely trying to sell their bits and pieces. Sure, some of the Japanese stuff is used on their race cars, but that doesn't make them any more legitimate.
Second, sure some of these items are probably "wind tunnel tested" but what difference does that make. So what if they could hang something off the rear of the car and be able to detect a change in the airflow. You can also hold your hand out the window and increase downforce.
I guarantee that when any of these items are used on real racing cars they are properly loaded with belly pans that extend to the center of pressure. Additionally, the diffusers on race cars are used at a much lower ride height.
Check out the diffuser on the Oreca Vipers. It runs 4 feet under the car and its blades are barely a hand thickness off the ground.
The point is that nobody is going to get ANY benefit from running one of these decorative items on their street car. Track guys may or may not want additional aerodynamic items on their cars. I have friends that have removed wings, splitters and other things as they learn how their car handles at high speed.
If you like how these diffusers look (and I do think some of them look neat), fine, quit lying to yourself believing that they perform anything whatsoever.
2/4 wheel cornering fiend
Joined: Nov 2002
Posts: 3,090
Likes: 3
From: Pasadena, CA
Originally Posted by WVRx7
Words mean things.
"Functional" is a generous term and cannot accurately be used to determine the worth of an item.
"Functional illiterate" is how school systems try to categorize someone that has been shuffled through the system, has been given passing grades and is generally liked by everyone. The sad thing is they can't read and write.
A 15 watt dome light bulb is functional as a headlight. It will illuminate the front of the car. Just because it is functional, it doesn't mean it functions in the job it is being used for.
First, believe no claims from any vendor. These people are merely trying to sell their bits and pieces. Sure, some of the Japanese stuff is used on their race cars, but that doesn't make them any more legitimate.
Second, sure some of these items are probably "wind tunnel tested" but what difference does that make. So what if they could hang something off the rear of the car and be able to detect a change in the airflow. You can also hold your hand out the window and increase downforce.
I guarantee that when any of these items are used on real racing cars they are properly loaded with belly pans that extend to the center of pressure. Additionally, the diffusers on race cars are used at a much lower ride height.
Check out the diffuser on the Oreca Vipers. It runs 4 feet under the car and its blades are barely a hand thickness off the ground.
The point is that nobody is going to get ANY benefit from running one of these decorative items on their street car. Track guys may or may not want additional aerodynamic items on their cars. I have friends that have removed wings, splitters and other things as they learn how their car handles at high speed.
If you like how these diffusers look (and I do think some of them look neat), fine, quit lying to yourself believing that they perform anything whatsoever.
"Functional" is a generous term and cannot accurately be used to determine the worth of an item.
"Functional illiterate" is how school systems try to categorize someone that has been shuffled through the system, has been given passing grades and is generally liked by everyone. The sad thing is they can't read and write.
A 15 watt dome light bulb is functional as a headlight. It will illuminate the front of the car. Just because it is functional, it doesn't mean it functions in the job it is being used for.
First, believe no claims from any vendor. These people are merely trying to sell their bits and pieces. Sure, some of the Japanese stuff is used on their race cars, but that doesn't make them any more legitimate.
Second, sure some of these items are probably "wind tunnel tested" but what difference does that make. So what if they could hang something off the rear of the car and be able to detect a change in the airflow. You can also hold your hand out the window and increase downforce.
I guarantee that when any of these items are used on real racing cars they are properly loaded with belly pans that extend to the center of pressure. Additionally, the diffusers on race cars are used at a much lower ride height.
Check out the diffuser on the Oreca Vipers. It runs 4 feet under the car and its blades are barely a hand thickness off the ground.
The point is that nobody is going to get ANY benefit from running one of these decorative items on their street car. Track guys may or may not want additional aerodynamic items on their cars. I have friends that have removed wings, splitters and other things as they learn how their car handles at high speed.
If you like how these diffusers look (and I do think some of them look neat), fine, quit lying to yourself believing that they perform anything whatsoever.
Joined: Jul 2001
Posts: 10,672
Likes: 413
From: Charlottesville VA 22901
It is actually useful if your going about 140 plus mph. I had one I my car and it worked fairly well. Check out the new EVO M car it has similar type grooves on the trailing end of the roof top. Essentially its designed to increase the flow of air underneath your car from front to back reducing lift. IMO its also the best looking rear diffuser that I've seen for the FD.
Did I mention that I have one for sale
Did I mention that I have one for sale
Last edited by Fritz Flynn; Dec 7, 2007 at 09:01 PM.
Thread Starter
Joined: May 2003
Posts: 4,150
Likes: 0
From: CA (Bay Area)
Originally Posted by Fritz Flynn
It is actually useful if your going about 140 plus mph. I had one I my car and it worked fairly well. Check out the new EVO M car it has similar type grooves on the trailing end of the roof top. Essentially its designed to increase the flow of air underneath your car from front to back reducing lift. IMO its also the best looking rear diffuser that I've seen for the FD.
Did I mention that I have one for sale
Did I mention that I have one for sale
oh one last thing... what is the difference between this rear diffuser, and a venturi tunnel that come on cars such as the porche carrera GT... the venturi tunnels actually PULL the car down by accelerating the air and causing different pressures correct ?
Full Member
Joined: Mar 2001
Posts: 213
Likes: 0
From: Charleston, WV, USA
Originally Posted by Fritz Flynn
It is actually useful if your going about 140 plus mph. I had one I my car and it worked fairly well. Check out the new EVO M car it has similar type grooves on the trailing end of the roof top. Essentially its designed to increase the flow of air underneath your car from front to back reducing lift. IMO its also the best looking rear diffuser that I've seen for the FD.
Did I mention that I have one for sale
Did I mention that I have one for sale
the time (with many friends of mine), but I have to ask
what you mean "worked fairly well".
Could you actually discern something that the "diffuser" was doing?
Did it actually effect the handling in such a way that you needed
to compensate with some other setting (tire pressures, shock or bar settings)
Could you have done a double blind comparison and been able to detect which
lap the thing was installed on the car. Say, a lap of the full course at
VIR, if it was on the car and then removed, or vice versa, could you
have been able to tell?
Lastly, if you believe you could tell a difference, just what was it?
I just don't believe it, but I will say I defer to you on speed and track time.
I could be wrong, but it would have to be proven for me to believe it.
What do you want for that thing? I do like how they look, but if I had it, I
would never stand in a mall parking lot and brag to others how it helps
me take exit ramps faster (as I have heard someone in a 240sx exclaim)
Last edited by WVRx7; Sep 6, 2004 at 10:37 PM.
Slam Pig
Joined: Dec 2002
Posts: 888
Likes: 0
From: New York
Originally Posted by WVRx7
Fritz, I know you know your stuff and you do track events all
the time (with many friends of mine), but I have to ask
what you mean "worked fairly well".
Could you actually discern something that the "diffuser" was doing?
Did it actually effect the handling in such a way that you needed
to compensate with some other setting (tire pressures, shock or bar settings)
Could you have done a double blind comparison and been able to detect which
lap the thing was installed on the car. Say, a lap of the full course at
VIR, if it was on the car and then removed, or vice versa, could you
have been able to tell?
Lastly, if you believe you could tell a difference, just what was it?
I just don't believe it, but I will say I defer to you on speed and track time.
I could be wrong, but it would have to be proven for me to believe it.
What do you want for that thing? I do like how they look, but if I had it, I
would never stand in a mall parking lot and brag to others how it helps
me take exit ramps faster (as I have heard someone in a 240sx exclaim)
the time (with many friends of mine), but I have to ask
what you mean "worked fairly well".
Could you actually discern something that the "diffuser" was doing?
Did it actually effect the handling in such a way that you needed
to compensate with some other setting (tire pressures, shock or bar settings)
Could you have done a double blind comparison and been able to detect which
lap the thing was installed on the car. Say, a lap of the full course at
VIR, if it was on the car and then removed, or vice versa, could you
have been able to tell?
Lastly, if you believe you could tell a difference, just what was it?
I just don't believe it, but I will say I defer to you on speed and track time.
I could be wrong, but it would have to be proven for me to believe it.
What do you want for that thing? I do like how they look, but if I had it, I
would never stand in a mall parking lot and brag to others how it helps
me take exit ramps faster (as I have heard someone in a 240sx exclaim)
Just gonna chime in with my $0.02 on how I understand that these work and what may be felt from it...For starters if these didnt do a damn thing I dont think every car from WRC to ALMS to F1 would be using this technology to some extent
I thought the purpose of a rear diffuser was to suck the car down to the ground...unlike a wing which guides air over the top of it creating downforce this would create a negative pressure at the rear of the car thus making a suction pulling the car down...
Though for these to work I think the underbody of the car has to be taken into affect as air has to channelled correctly into it......
like that on a ferrari 550.......
I also though that one cars that were really setup for these would get loose in a turn when the air wasnt directly flowing out the back..or when the car went over a curb and disturbed the air....
just my $0.02...I do love physics and cars though
and this could be all wrong...
Super Snuggles
Joined: Feb 2001
Posts: 10,091
Likes: 34
From: Redmond, WA
Originally Posted by obviousboy
For starters if these didnt do a damn thing I dont think every car from WRC to ALMS to F1 would be using this technology to some extent
F1 cars use spoilers front and rear to produce downforce. Does that make a VeilSide body kit a performance improvement at high speed because it has front and rear spoilers, or is it just an appearance change that may or may not be stable at high speed, and in fact could be dangerous at high speed? Only a wind tunnel knows for sure.
or when the car went over a curb and disturbed the air...
I guess running a datalogger on suspesion compression would be the only way to truly test it. I'm sure that's what all those higher-end japanese companies do on their 8 mile high speed ovals. I see them using those tracks all the time in JDM videos.
No it's not Turbo'd
Joined: Jun 2002
Posts: 2,511
Likes: 2
From: Los Angeles, Ca
Okay Yes I have one, no I'm not selling mine or trying to convice anybody, least of all myself that this is a "Performance Enhancer" @ Even "Semi" legal Road Speeds.
It is for looks !
Now having said that, you have to look at the stock setup, it's a plastic shroud that hides the gas tank and protrudes directly into the airflow and scoops up air over the gas tank... I know I was in the desert (dry lake bed) , and after washing the car, and trying to install a new gas pump found 1/4" thick layer of sand on the top of the tank.... to the point.
No it's not a performance enhancer, but it does seem to cover up / protect the gas tank, as well as prevent a lot of air circulating and causing turbulance at the rear of the car, at just about any foreward movement. Can you feel this, probhably not, can you measure it, maybe as an increase in fuel milage (MPG)... but I'm not old enough to be able to stay off the boost through a whole tank of gas...
It is for looks !
Now having said that, you have to look at the stock setup, it's a plastic shroud that hides the gas tank and protrudes directly into the airflow and scoops up air over the gas tank... I know I was in the desert (dry lake bed) , and after washing the car, and trying to install a new gas pump found 1/4" thick layer of sand on the top of the tank.... to the point.
No it's not a performance enhancer, but it does seem to cover up / protect the gas tank, as well as prevent a lot of air circulating and causing turbulance at the rear of the car, at just about any foreward movement. Can you feel this, probhably not, can you measure it, maybe as an increase in fuel milage (MPG)... but I'm not old enough to be able to stay off the boost through a whole tank of gas...
Birds can DRIFT YO...!!!!
Joined: Oct 2002
Posts: 697
Likes: 1
From: California
Originally Posted by DCrosby
Okay Yes I have one, no I'm not selling mine or trying to convice anybody, least of all myself that this is a "Performance Enhancer" @ Even "Semi" legal Road Speeds.
It is for looks !
Now having said that, you have to look at the stock setup, it's a plastic shroud that hides the gas tank and protrudes directly into the airflow and scoops up air over the gas tank... I know I was in the desert (dry lake bed) , and after washing the car, and trying to install a new gas pump found 1/4" thick layer of sand on the top of the tank.... to the point.
No it's not a performance enhancer, but it does seem to cover up / protect the gas tank, as well as prevent a lot of air circulating and causing turbulance at the rear of the car, at just about any foreward movement. Can you feel this, probhably not, can you measure it, maybe as an increase in fuel milage (MPG)... but I'm not old enough to be able to stay off the boost through a whole tank of gas...
It is for looks !
Now having said that, you have to look at the stock setup, it's a plastic shroud that hides the gas tank and protrudes directly into the airflow and scoops up air over the gas tank... I know I was in the desert (dry lake bed) , and after washing the car, and trying to install a new gas pump found 1/4" thick layer of sand on the top of the tank.... to the point.
No it's not a performance enhancer, but it does seem to cover up / protect the gas tank, as well as prevent a lot of air circulating and causing turbulance at the rear of the car, at just about any foreward movement. Can you feel this, probhably not, can you measure it, maybe as an increase in fuel milage (MPG)... but I'm not old enough to be able to stay off the boost through a whole tank of gas...
Slam Pig
Joined: Dec 2002
Posts: 888
Likes: 0
From: New York
Originally Posted by jimlab
And how would that keep companies from producing parts that look like racing parts but provide little or no measurable benefit?
F1 cars use spoilers front and rear to produce downforce. Does that make a VeilSide body kit a performance improvement at high speed because it has front and rear spoilers, or is it just an appearance change that may or may not be stable at high speed, and in fact could be dangerous at high speed? Only a wind tunnel knows for sure.
If you're going over curbs, you have more to worry about than disturbing the air...
F1 cars use spoilers front and rear to produce downforce. Does that make a VeilSide body kit a performance improvement at high speed because it has front and rear spoilers, or is it just an appearance change that may or may not be stable at high speed, and in fact could be dangerous at high speed? Only a wind tunnel knows for sure.
If you're going over curbs, you have more to worry about than disturbing the air...
I didnt mean that kinda of curb..good catch though
What is the part on a track that is painted red and white around a turn..I always though it was a curb.....
No it's not Turbo'd
Joined: Jun 2002
Posts: 2,511
Likes: 2
From: Los Angeles, Ca
Originally Posted by birdy01
lolz damn 1/4' huh
