Side Exhausts and aerodynamics with pics
01-03-2010, 08:11 AM
#16
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O.K I thought I would share some of my research, turned up some interesting facts along with some questions, there is quite a plethora of information out there regarding aerodynamic testing without CFD or a wind tunnel. When I went looking there was some good basic stuff that even F1 cars were being tested with. I am not sure they (F1 Teams) are still doing these tests due to the testing ban that came in in 2009. I saw Williams testing on a runway on Youtube.
What is done and Racecar Engineering did a recent article on this and how to do it on the cheap, was fit pots to the suspension arms and you will also need a potentiometer on the throttle to read the exact position. The pots will read the down force and the throttle position relative to speed will tell you the drag.
Autospeed also did some interesting articles, some are listed at the beginning of the thread but there is also a few extra out there and they detail how small changes can bring about some rather big changes, most of the big changes were bad. Interesting lift figures were gathered and also pressures under the bonnet/hood were taken. They were also using a type of pot for this work.
That high pressure was an interesting fact, I do at this stage plan to vent the bonnet with some very discreet but functional vents, Gordon Murray likes them anyway.
Tie them with the guard/fender ducts it will be interesting to see how much the drag/turbulence is changed? Maybe some of the radiator area could then be taped off or the shutters run so as to reduce airflow?
The other factor of course is the increased cooling the ducting provides, this allows proportionally smaller radiators and coolers as these parts become more efficient. This of course saves weight and off the front end to boot.
On the design of the side skirts I do have a semi finalized design, it is somewhat similar to the Monaro but with key Porsche 928 styling elements. One of the efficiencies you strive for as a designer of aero pieces is to stop the leaks to the underbody.
Race car designers particularly of open wheelers, try to stop the leaks by creating vortices, these disrupt the leakage. Obviously the best system was the skirt system used back in the 80s. I did have another idea that might fly with a front engined GT car.
With the McLaren SLR the exhaust was designed to exit at rear of the front guards, this was to keep the floor uncluttered and then they went and put big hex head cap screws to ruin it
.
The principle remains run as much air under the car and run it against a smooth surface and accelerate it and create a low pressure zone, this is your downforce. Of course there is other parts of the car that produce downforce, like the splitter and the rear wing if there is one.
The areas that need treatment are in front of the front wheels, this would only be on the 928 and 928S, the S4 and later models have this area addressed, in front of the rear wheels, especially when wide wheels are fitted and also to keep the air away from the front of the tyres to avoid lift and drive the diffuser.
It was interesting to note that the Ferrari 599 rake angle is quite pronounced like the Monaro, the measurement I got at the front splitter was 95 mm and in front of the rear wheels it was 130 mm. The diffuser starts just in front of the rear axle, this effects where the pressure balance ends
What is done and Racecar Engineering did a recent article on this and how to do it on the cheap, was fit pots to the suspension arms and you will also need a potentiometer on the throttle to read the exact position. The pots will read the down force and the throttle position relative to speed will tell you the drag.
Autospeed also did some interesting articles, some are listed at the beginning of the thread but there is also a few extra out there and they detail how small changes can bring about some rather big changes, most of the big changes were bad. Interesting lift figures were gathered and also pressures under the bonnet/hood were taken. They were also using a type of pot for this work.
That high pressure was an interesting fact, I do at this stage plan to vent the bonnet with some very discreet but functional vents, Gordon Murray likes them anyway.
Tie them with the guard/fender ducts it will be interesting to see how much the drag/turbulence is changed? Maybe some of the radiator area could then be taped off or the shutters run so as to reduce airflow?The other factor of course is the increased cooling the ducting provides, this allows proportionally smaller radiators and coolers as these parts become more efficient. This of course saves weight and off the front end to boot.
On the design of the side skirts I do have a semi finalized design, it is somewhat similar to the Monaro but with key Porsche 928 styling elements. One of the efficiencies you strive for as a designer of aero pieces is to stop the leaks to the underbody.
Race car designers particularly of open wheelers, try to stop the leaks by creating vortices, these disrupt the leakage. Obviously the best system was the skirt system used back in the 80s. I did have another idea that might fly with a front engined GT car.
With the McLaren SLR the exhaust was designed to exit at rear of the front guards, this was to keep the floor uncluttered and then they went and put big hex head cap screws to ruin it
.The principle remains run as much air under the car and run it against a smooth surface and accelerate it and create a low pressure zone, this is your downforce. Of course there is other parts of the car that produce downforce, like the splitter and the rear wing if there is one.
The areas that need treatment are in front of the front wheels, this would only be on the 928 and 928S, the S4 and later models have this area addressed, in front of the rear wheels, especially when wide wheels are fitted and also to keep the air away from the front of the tyres to avoid lift and drive the diffuser.
It was interesting to note that the Ferrari 599 rake angle is quite pronounced like the Monaro, the measurement I got at the front splitter was 95 mm and in front of the rear wheels it was 130 mm. The diffuser starts just in front of the rear axle, this effects where the pressure balance ends
Last edited by slate blue; 05-20-2012 at 06:12 AM.
01-04-2010, 01:00 AM
#17
Intermediate
Regarding your exhaust statement. I had a 3" custom exhaust installed on my 83 euro with magnaflow muffler and it does make a performance difference and some weight savings.
I had to install a hi flow cat but recently bought emission free tags and will replace it with a small resonator.
I had to install a hi flow cat but recently bought emission free tags and will replace it with a small resonator.
01-04-2010, 09:44 AM
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Hamm thanks for your post, did you get a duel 3" or a single? I feel the only reason my 3" is successful in such a small motor is that the bypass valve boosts the torque
Last edited by slate blue; 05-19-2012 at 07:37 PM.
01-04-2010, 10:06 AM
#19
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Here's a link with some basic but interesting info,
http://www.forocoches.com/foro/showthread.php?t=538531
http://www.forocoches.com/foro/showthread.php?t=538531
Last edited by slate blue; 05-19-2012 at 07:47 PM.
01-04-2010, 05:36 PM
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Saw the pictures of that car and was wondering if you did want to have your pipes come out the side in front of the rear wheel where would you put the muffler? It just seems that you could get those 3in pipes that are kinda flattened to help with clearence but the muffler doesn't seem like it will fit anywhere practical.
Cheers,
89 5speed hybrid
Cheers,
89 5speed hybrid
01-04-2010, 05:39 PM
#21
Nordschleife Master
Greg,
I will be going with 3" pipes out the frame rails of the engine bay just infront of the firewall and down the side of the car on my twin turbo car...
I will be going with 3" pipes out the frame rails of the engine bay just infront of the firewall and down the side of the car on my twin turbo car...
01-04-2010, 06:36 PM
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Ray in my state, it is not allowed to exit the exhausts at the side. So I am not allowed to do this for street use. In fact there is room for the mufflers. The program, Pipemax actually says that an exhaust exiting in front of the rear wheels, is the perfect tuned length.
The exhaust would be slightly louder than the one that is one the car at present which is quiet under normal operation it makes a great great sound. So much so when the fellow at the inspection station heard me coming and the customer he was talking to said, "We wondered what was coming, sounds unbelievably good, that can't be legal!"
Colin that is going to be a fair bit of work.
The exhaust would be slightly louder than the one that is one the car at present which is quiet under normal operation it makes a great great sound. So much so when the fellow at the inspection station heard me coming and the customer he was talking to said, "We wondered what was coming, sounds unbelievably good, that can't be legal!"
Colin that is going to be a fair bit of work.
Last edited by slate blue; 05-19-2012 at 07:35 PM.
01-04-2010, 06:50 PM
#24
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Basically, you want the splitter to keep the air from rolling off the nose to go under the car. more air forced under the car, the less the downforce compared to keeping the air from traveling under the car to begin with. thats the key point. any air that would have rolled under the car, that didnt go into the radiator, would be routed around to the sides of the car. the air into the radiator, then is vented to the hood vent, located at the lowest pressure zone. (i.e. our cars, about in the 1 foot from the edge of the front bonnet/hoodline)
This also gives more air going over the car to make the wings more effective in the rear.
the under the car dynamics are more complicated. generally, you have just ambient air pressure at most all sections over the car, where the high pressure zones at the nose and base of windshield are near .2psi, at near 120mph. the vacuum at all other areas is not quite as much in the other direction but span most of the length of the vehicle.
so, under the car, venturie channels are used to slightly lower the pressure and speed up that air, even further for the air that does make it under the car, and keep the ambient pressure to the outside, alongthe doors from going under the car and increase lift (pressure). at the rear, defusers would then be needed to vent the air to the rear, slow it down and return it to the ambient pressure as it exits. most of the under car work is smooth to reduce drag of the air traveling under the car. without under trays, its like that air is passing over a covertable. (well , not quite, but you get the picture).
spend most of the time and effort in making hood vents and splitters for most effective downforce, and if you want 200mph aero benefits, pan off the entire under tray. at race car track speeds, its not a big deal, so I wouldnt worry about it. most of the the drag is the size of the car anyway, along with any wings used for downforce. turbulent flow under the car at less than 100mph is not too much of a cost, in otherwords.
This also gives more air going over the car to make the wings more effective in the rear.
the under the car dynamics are more complicated. generally, you have just ambient air pressure at most all sections over the car, where the high pressure zones at the nose and base of windshield are near .2psi, at near 120mph. the vacuum at all other areas is not quite as much in the other direction but span most of the length of the vehicle.
so, under the car, venturie channels are used to slightly lower the pressure and speed up that air, even further for the air that does make it under the car, and keep the ambient pressure to the outside, alongthe doors from going under the car and increase lift (pressure). at the rear, defusers would then be needed to vent the air to the rear, slow it down and return it to the ambient pressure as it exits. most of the under car work is smooth to reduce drag of the air traveling under the car. without under trays, its like that air is passing over a covertable. (well , not quite, but you get the picture).
spend most of the time and effort in making hood vents and splitters for most effective downforce, and if you want 200mph aero benefits, pan off the entire under tray. at race car track speeds, its not a big deal, so I wouldnt worry about it. most of the the drag is the size of the car anyway, along with any wings used for downforce. turbulent flow under the car at less than 100mph is not too much of a cost, in otherwords.
O.K I thought I would share some of my research, turned up some interesting facts along with some questions, there is quite a plethora of information out there regarding aerodynamic testing without CFD or a wind tunnel. When I went looking there was some good basic stuff that even F1 cars were being tested with. I am not sure they (F1 Teams) are still doing these tests due to the testing ban that came in in 2009. I saw Williams testing on a runway on Youtube.
That high pressure was an interesting fact, I do at this stage plan to vent the bonnet with some very discreet but functional vents, Gordon Murray likes them anyway. Tie them with the guard/fender ducts it will be interesting to see how much the drag/turbulence is changed? Maybe some of the radiator area could then be taped off or the shutters run so as to reduce airflow?
The other factor of course is the increased cooling the ducting provides, this allows proportionally smaller radiators and coolers as these parts become more efficient. This of course saves weight and off the front end to boot.
On the design of the side skirts I do have a semi finalized design, it is somewhat similar to the Monaro but with key Porsche 928 styling elements. One of the efficiencies you strive for as a designer of aero pieces is to stop the leaks to the underbody.
Race car designers particularly of open wheelers, try to stop the leaks by creating vortices, these disrupt the leakage. Obviously the best system was the skirt system used back in the 80s. I did have another idea that might fly with a front engined GT car.
How about an air curtain? Just like the ones that keep flies out of shops, the air that is needed to come into the engine bay for cooling is normally just re-routed in the case of the 928 it exits around the area where the cats are. To be efficient the floor must be flat, flatter the better, just like wings less supports the better, that is the wing will be more efficient.
With the McLaren SLR the exhaust was designed to exit at rear of the front guards, this was to keep the floor uncluttered and then they went and put big hex head cap screws to ruin it.
The principle remains run as much air under the car and run it against a smooth surface and accelerate it and create a low pressure zone, this is your downforce. Of course there is other parts of the car that produce downforce, like the splitter and the rear wing if there is one.
So instead of running the air to the rear or all to the rear, why not vent it at the side skirts progressively? So as to create a curtain or air along with any vortices to keep the air flowing as uninterrupted as possible. The air pressure would not want to get too high in this area otherwise you had defeated yourself.
Anyway thought I would share some info and ideas.
Greg
That high pressure was an interesting fact, I do at this stage plan to vent the bonnet with some very discreet but functional vents, Gordon Murray likes them anyway.
Tie them with the guard/fender ducts it will be interesting to see how much the drag/turbulence is changed? Maybe some of the radiator area could then be taped off or the shutters run so as to reduce airflow?The other factor of course is the increased cooling the ducting provides, this allows proportionally smaller radiators and coolers as these parts become more efficient. This of course saves weight and off the front end to boot.
On the design of the side skirts I do have a semi finalized design, it is somewhat similar to the Monaro but with key Porsche 928 styling elements. One of the efficiencies you strive for as a designer of aero pieces is to stop the leaks to the underbody.
Race car designers particularly of open wheelers, try to stop the leaks by creating vortices, these disrupt the leakage. Obviously the best system was the skirt system used back in the 80s. I did have another idea that might fly with a front engined GT car.
How about an air curtain? Just like the ones that keep flies out of shops, the air that is needed to come into the engine bay for cooling is normally just re-routed in the case of the 928 it exits around the area where the cats are. To be efficient the floor must be flat, flatter the better, just like wings less supports the better, that is the wing will be more efficient.
With the McLaren SLR the exhaust was designed to exit at rear of the front guards, this was to keep the floor uncluttered and then they went and put big hex head cap screws to ruin it
.The principle remains run as much air under the car and run it against a smooth surface and accelerate it and create a low pressure zone, this is your downforce. Of course there is other parts of the car that produce downforce, like the splitter and the rear wing if there is one.
So instead of running the air to the rear or all to the rear, why not vent it at the side skirts progressively? So as to create a curtain or air along with any vortices to keep the air flowing as uninterrupted as possible. The air pressure would not want to get too high in this area otherwise you had defeated yourself.
Anyway thought I would share some info and ideas.
Greg
01-05-2010, 12:11 AM
#25
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Mark thanks for your response, from my understanding the splitter which is very small on my car (and may require a proper race one for track days, as a bigger one would make getting around Sydney pretty tough) develops some downforce at the cost of drag and increased frontal area.
I am facing a tough assignment here, there is styling issues that I don't want to compromise on and then we have function. The spoiler worked on the front of the S by shutting off some of the air getting underneath the car. That air created extra drag and lift. So that was a pretty straight forward job for porsche. That spoiler is a spoiler or air dam as it has nothing behind it.
It changes when you hook up a floor to it as the air cannot get behind it. The other aspect that changes is when a complete flat floor is fitted you want as much air under the car as possible. So then the spoiler acting as an air dam is counter productive. This is one reason for me trying to turn it from a spoiler to a splitter. That way I can make it earn its keep. That little splitter off the GT3RS has a rounder edge for what I suspect a less draggy design than a 90 degree corner.
Also I would just say that I have not formed a definite opinion about the benefits at various speeds on the racetrack. I agree that it matters more the faster you go. I would also say a great big GT3 style rear wing and equal front splitter would make a very big difference in terms of lap times. Who knows I may just bolt them on and off at the track if I wish?
I think what we do know is if I was or anybody else for that matter bolt on a splitter and rear wing like that it will be much more efficient on that car than a car without that aero work. The diffuser and the rear wing are normally made to work together.
As a rule of thumb a 10 degree angle on a diffuser is the maximum angle for the best downforce and drag. You can run up to 14 degrees but with extra drag and no extra downforce. Now for those of you that have been up close to F1 cars you will know that their diffuser are steeper than that, a fair bit steeper. Why? Well the rear wing and the diffuser work together and this allows a steeper efficient angle. It is where 1+1=3 Something for nothing.
I am just copying a design that works and trying to adapt it well and improve on areas that Ferrari did a bit less than perfect. The 599 has figures for its downforce at various speeds, I will look them up but they are impressive especially when you realise from our position you will be canceling out some lift. I am also doing this as a styling revisit which I hope is very well considered, I just wished I could draw, I may well have a go at it but I think it is outside my abilities.
I am facing a tough assignment here, there is styling issues that I don't want to compromise on and then we have function. The spoiler worked on the front of the S by shutting off some of the air getting underneath the car. That air created extra drag and lift. So that was a pretty straight forward job for porsche. That spoiler is a spoiler or air dam as it has nothing behind it.
It changes when you hook up a floor to it as the air cannot get behind it. The other aspect that changes is when a complete flat floor is fitted you want as much air under the car as possible. So then the spoiler acting as an air dam is counter productive. This is one reason for me trying to turn it from a spoiler to a splitter. That way I can make it earn its keep. That little splitter off the GT3RS has a rounder edge for what I suspect a less draggy design than a 90 degree corner.
Also I would just say that I have not formed a definite opinion about the benefits at various speeds on the racetrack. I agree that it matters more the faster you go. I would also say a great big GT3 style rear wing and equal front splitter would make a very big difference in terms of lap times. Who knows I may just bolt them on and off at the track if I wish?
I think what we do know is if I was or anybody else for that matter bolt on a splitter and rear wing like that it will be much more efficient on that car than a car without that aero work. The diffuser and the rear wing are normally made to work together.
As a rule of thumb a 10 degree angle on a diffuser is the maximum angle for the best downforce and drag. You can run up to 14 degrees but with extra drag and no extra downforce. Now for those of you that have been up close to F1 cars you will know that their diffuser are steeper than that, a fair bit steeper. Why? Well the rear wing and the diffuser work together and this allows a steeper efficient angle. It is where 1+1=3 Something for nothing.
I am just copying a design that works and trying to adapt it well and improve on areas that Ferrari did a bit less than perfect. The 599 has figures for its downforce at various speeds, I will look them up but they are impressive especially when you realise from our position you will be canceling out some lift. I am also doing this as a styling revisit which I hope is very well considered, I just wished I could draw, I may well have a go at it but I think it is outside my abilities.
Last edited by slate blue; 05-18-2012 at 09:08 PM.
01-05-2010, 12:51 AM
#26
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Actually, the splitter is one of those "no cost" devices. the air could run down the the nose and run under the car, or it can be diverted to the sides of the car. If you have a flat faced car all you need is an air dam, for near the same effect. the fact that we have a nose on the front of the 928, requires a splittler to keep the air rolling down from the mid point, from going under the car. The frontal area doesnt increase, and the only drag, is frictional drag forces that the car will have with increased downforce in front. if you think about ALMS cars or Daytona Prototypes, they need very little splitters, as the on coming air just goes into scoop areas that feed the radiator and vent to the hood. someone with an old body here, showed an added splitter that looked very good. If you want effectiveness, do that. If you cant live with the size and protrusion of a splitter, vent the massive inlet to the hood. (just past the radiator and before the top of the oil filler)
There is nothing to the fact that there is "nothing "behind" the air dam. the air is being split to the sides due to its shape, but still can roll off the bottom and under the car. there is more turbulence now, as it travels under the car because of the curling of the air flow as it passes over the air dam. Ive measured and tested these air flow characteristics found with and without splitters as well as looking at flow under the car.
To the GT3 reference, its splitter or when it doesnt have one, has a shape to divert the air to the sides of the car, as it has a flat face (no nose like the 928)
Dont drive yourself too crazy over it. for the most part the aero doesnt make HUGE differences, but it does make the car more controllable, especially in awkward attitudes in a race. the speeds are just so slow with most tracks we go to . road america, willow springs, much more so. So it really depends on how fast you are going around the track.
remember as ugly as the splitter I used was, it was effective and worked. (along with the hood vent) it solved a push problem and allowed me to use more wing. remember, I also HAVE the GT3 wing. lap times were very close to the same. I would say, best case, it gave .3-.5 of a second, max.
There is nothing to the fact that there is "nothing "behind" the air dam. the air is being split to the sides due to its shape, but still can roll off the bottom and under the car. there is more turbulence now, as it travels under the car because of the curling of the air flow as it passes over the air dam. Ive measured and tested these air flow characteristics found with and without splitters as well as looking at flow under the car.
To the GT3 reference, its splitter or when it doesnt have one, has a shape to divert the air to the sides of the car, as it has a flat face (no nose like the 928)
Dont drive yourself too crazy over it. for the most part the aero doesnt make HUGE differences, but it does make the car more controllable, especially in awkward attitudes in a race. the speeds are just so slow with most tracks we go to . road america, willow springs, much more so. So it really depends on how fast you are going around the track.
remember as ugly as the splitter I used was, it was effective and worked. (along with the hood vent) it solved a push problem and allowed me to use more wing. remember, I also HAVE the GT3 wing. lap times were very close to the same. I would say, best case, it gave .3-.5 of a second, max.
Mark thanks for your response, from my understanding the splitter which is very small on my car (and may require a proper race one for track days, as a bigger one would make getting around Sydney pretty tough) develops some downforce at the cost of drag and increased frontal area.
I am facing a tough assignment here, there is styling issues that I don't want to compromise on and then we have function. The spoiler worked on the front of the S by shutting off some of the air getting underneath the car. That air created extra drag and lift. So that was a pretty straight forward job for porsche. That spoiler is a spoiler or air dam as it has nothing behind it.
It changes when you hook up a floor to it as the air cannot get behind it. The other aspect that changes is when a complete flat floor is fitted you want as much air under the car as possible. So then the spoiler acting as an air dam is counter productive. This is one reason for me trying to turn it from a spoiler to a splitter. That way I can make it earn its keep. That little splitter off the GT3RS has a rounder edge for what I suspect a less draggy design than a 90 degree corner.
Also I would just say that I have not formed a definite opinion about the benefits at various speeds on the racetrack. I agree that it matters more the faster you go. I would also say a great big GT3 style rear wing and equal front splitter would make a very big difference in terms of lap times. Who knows I may just bolt them on and off at the track if I wish?
I think what we do know is if I was or anybody else for that matter bolt on a splitter and rear wing like that it will be much more efficient on that car than a car without that aero work. The diffuser and the rear wing are normally made to work together.
As a rule of thumb a 10 degree angle on a diffuser is the maximum angle for the best downforce and drag. You can run up to 14 degrees but with extra drag and no extra downforce. Now for those of you that have been up close to F1 cars you will know that their diffuser are steeper than that, a fair bit steeper. Why? Well the rear wing and the diffuser work together and this allows a steeper efficient angle. It is where 1+1=3 Something for nothing.
I am just copying a design that works and trying to adapt it well and improve on areas that Ferrari did a bit less than perfect. The 599 has figures for its downforce at various speeds, I will look them up but they are impressive especially when you realise from our position you will be canceling out some lift. I am also doing this as a styling revisit which I hope is very well considered, I just wished I could draw, I may well have a go at it but I think it is outside my abilities.
Greg
I am facing a tough assignment here, there is styling issues that I don't want to compromise on and then we have function. The spoiler worked on the front of the S by shutting off some of the air getting underneath the car. That air created extra drag and lift. So that was a pretty straight forward job for porsche. That spoiler is a spoiler or air dam as it has nothing behind it.
It changes when you hook up a floor to it as the air cannot get behind it. The other aspect that changes is when a complete flat floor is fitted you want as much air under the car as possible. So then the spoiler acting as an air dam is counter productive. This is one reason for me trying to turn it from a spoiler to a splitter. That way I can make it earn its keep. That little splitter off the GT3RS has a rounder edge for what I suspect a less draggy design than a 90 degree corner.
Also I would just say that I have not formed a definite opinion about the benefits at various speeds on the racetrack. I agree that it matters more the faster you go. I would also say a great big GT3 style rear wing and equal front splitter would make a very big difference in terms of lap times. Who knows I may just bolt them on and off at the track if I wish?
I think what we do know is if I was or anybody else for that matter bolt on a splitter and rear wing like that it will be much more efficient on that car than a car without that aero work. The diffuser and the rear wing are normally made to work together.
As a rule of thumb a 10 degree angle on a diffuser is the maximum angle for the best downforce and drag. You can run up to 14 degrees but with extra drag and no extra downforce. Now for those of you that have been up close to F1 cars you will know that their diffuser are steeper than that, a fair bit steeper. Why? Well the rear wing and the diffuser work together and this allows a steeper efficient angle. It is where 1+1=3 Something for nothing.
I am just copying a design that works and trying to adapt it well and improve on areas that Ferrari did a bit less than perfect. The 599 has figures for its downforce at various speeds, I will look them up but they are impressive especially when you realise from our position you will be canceling out some lift. I am also doing this as a styling revisit which I hope is very well considered, I just wished I could draw, I may well have a go at it but I think it is outside my abilities.
Greg
01-05-2010, 01:07 AM
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01-05-2010, 06:43 AM
#28
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Well I hope those ducts do look good, I suppose it will depend on the welder, however while they are not the ultimate and as I mentioned before there is a balance to be had in this case between aesthetics and function.
The vents may well surprise you as they are rearward facing I think what you may have failed to consider is that the pressure in the engine bay along with the suction of the air running over the body will make these very efficient for their size.
I am looking more at reducing the lift that is there plus reducing the drag, the 599 is a big car, bigger than a 928 but has a better Cd number, these vents/ducts are some of the reasons. Think about it, if there is a pressure build up there must be some drag being caused, let the air pressure escape, should be less drag.
Now if you want to take it a step further have a look at this car, this is probably more applicable than the examples you offered, the reason is the layout, front engined rear tranaxle, the exception being the Volvo but that is as ugly as a hat full of arseholes and I don't want to go there
This is the car's big brother from where I got my vents, it develops 280 kg of downforce at 125 mph, a speed I am sure it is constantly above!
You will notice the bonnet vents, all engine bay air exits through these vents, the engine bay is completely enclosed. The floor is basically flat but with a few tricks. Notice the lower front end treatment, this is what I mentioned before, guide the air away from the tyres and send plenty of air under the car.
By Mark kibort
I wasn't going to say anything here but you are sort of contradicting yourself here, the pure fact that you say there is turbulence now means there is a difference. You see when the put the flat floor and connect it to the air dam/spoiler you smooth out the flow and as such the air will run faster. Faster air will create a low pressure zone.
You are correct in saying there is turbulent air there but a more complete statement, would be, there is reduced air traveling under the car due to the air dam and there is a wake like low pressure turbulence behind it. To say there is no difference is wrong because while there is probably little difference in the actual results and I do note the examples you quote. However in my case there is a detailed underbody and then a diffuser. That then makes a world of difference.
Cheers Greg
, however while they are not the ultimate and as I mentioned before there is a balance to be had in this case between aesthetics and function.The vents may well surprise you as they are rearward facing I think what you may have failed to consider is that the pressure in the engine bay along with the suction of the air running over the body will make these very efficient for their size.
I am looking more at reducing the lift that is there plus reducing the drag, the 599 is a big car, bigger than a 928 but has a better Cd number, these vents/ducts are some of the reasons. Think about it, if there is a pressure build up there must be some drag being caused, let the air pressure escape, should be less drag.
Now if you want to take it a step further have a look at this car, this is probably more applicable than the examples you offered, the reason is the layout, front engined rear tranaxle, the exception being the Volvo but that is as ugly as a hat full of arseholes and I don't want to go there
This is the car's big brother from where I got my vents, it develops 280 kg of downforce at 125 mph, a speed I am sure it is constantly above!
You will notice the bonnet vents, all engine bay air exits through these vents, the engine bay is completely enclosed. The floor is basically flat but with a few tricks. Notice the lower front end treatment, this is what I mentioned before, guide the air away from the tyres and send plenty of air under the car. By Mark kibort
There is nothing to the fact that there is "nothing "behind" the air dam. the air is being split to the sides due to its shape, but still can roll off the bottom and under the car. there is more turbulence now, as it travels under the car because of the curling of the air flow as it passes over the air dam. Ive measured and tested these air flow characteristics found with and without splitters as well as looking at flow under the car.
You are correct in saying there is turbulent air there but a more complete statement, would be, there is reduced air traveling under the car due to the air dam and there is a wake like low pressure turbulence behind it. To say there is no difference is wrong because while there is probably little difference in the actual results and I do note the examples you quote. However in my case there is a detailed underbody and then a diffuser. That then makes a world of difference.
Cheers Greg
01-05-2010, 11:35 AM
#29
Rennlist Member
Greg,
Here are a couple of pictures of the splitter and diffuser that I built last year.
The splitter itself is 70 mm if I recall and trails back under the spoiler by about 13-14 inches. The diffuser is built at an angle of 17 degrees.
Ken
Here are a couple of pictures of the splitter and diffuser that I built last year.
The splitter itself is 70 mm if I recall and trails back under the spoiler by about 13-14 inches. The diffuser is built at an angle of 17 degrees.
Ken
01-05-2010, 11:40 AM
#30
Rennlist Member
While on the subject of adding a hood vent, I am trying to locate the factory hood vent that was used on the 968 Turbo RS.
I think I have located a source, but they may be too expensive for me to use.
I've seen an example of this on a red car and it looks great. You'll note that there is a slight up sweep to the leading edge to enhance airflow.
Regards,
Ken
I think I have located a source, but they may be too expensive for me to use.
I've seen an example of this on a red car and it looks great. You'll note that there is a slight up sweep to the leading edge to enhance airflow.
Regards,
Ken
