Last track day of the year for '06 - Thunderhill (new splitter,hood vent and wing )
01-01-2007, 11:02 PM
#16
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With those dive planes added, you've upgraded your S4 to an OB S air dam. 
I like the look of the rear mesh. I may have to steal that. One piece to cover both bumperette holes with a back plate, and also hang down to cover my trans cooler.
I like the look of the rear mesh. I may have to steal that. One piece to cover both bumperette holes with a back plate, and also hang down to cover my trans cooler.
01-01-2007, 11:32 PM
#17
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the grill is from Grillcraft.com I think it was $48 for the sheet that was easily enough for the hood and rear holes. its aluminum so its pretty stout, but light too.
riveted in the rear with 1/8 aluminum rivits and washers, and JBweld and gorilla glue on the hood. (that JB welld is amazing. its not going anywhere!)
mk
riveted in the rear with 1/8 aluminum rivits and washers, and JBweld and gorilla glue on the hood. (that JB welld is amazing. its not going anywhere!)
mk
Originally Posted by PorKen
With those dive planes added, you've upgraded your S4 to an OB S air dam.
I like the look of the rear mesh. I may have to steal that. One piece to cover both bumperette holes with a back plate, and also hang down to cover my trans cooler.
I like the look of the rear mesh. I may have to steal that. One piece to cover both bumperette holes with a back plate, and also hang down to cover my trans cooler.
01-03-2007, 01:34 AM
#18
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Mark, now you need to get some side skirts between the front and rear wheels to keep air from rolling under the sides. I've been looking for a good set for the 928, haven't been able to come with any. They wouldn't be hard to make if none are avialable...
Steve
Steve
01-03-2007, 07:29 AM
#19
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Mark
Your rear spoiler uprights , they look pretty thin to me, more than strong enough in the vertical plain but how about with some added sideways pressure on the end of the spoiler , how strong ? ,could it fold/collapse ?. How about some wire X bracing like on a bi-plane aircraft.
Thanks for all the detailed testing reports , I find them most interesting .
Best of luck for the upcoming season
Your rear spoiler uprights , they look pretty thin to me, more than strong enough in the vertical plain but how about with some added sideways pressure on the end of the spoiler , how strong ? ,could it fold/collapse ?. How about some wire X bracing like on a bi-plane aircraft.
Thanks for all the detailed testing reports , I find them most interesting .
Best of luck for the upcoming season
01-03-2007, 07:50 AM
#20
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Originally Posted by svp928
Mark, now you need to get some side skirts between the front and rear wheels to keep air from rolling under the sides. I've been looking for a good set for the 928, haven't been able to come with any. They wouldn't be hard to make if none are avialable...
Steve
Steve
drnick with the orange car here in the UK has some ,IIRC they are 996 modified to fit (maybe modified then a mold taken ), best pick I could find is on this thread
https://rennlist.com/forums/showthread.
01-03-2007, 09:39 AM
#21
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Originally Posted by mark kibort
That's a common misconception to a certain extent. The air entering the radiator vents underneath the car , unless you have a lot of belly pan coverage.
Having a bellypan on the car forces the air to go between it and the ground, causing that air to accelerate relative to 'ambient'; as a result, a low-pressure zone is created. Assuming the pressure under the hood is higher, the higher-pressure air under the hood it will then 'vent' into the lower pressure area under the bellypan via the bellypan's holes, thus allowing more flow through the radiator.
So a bellypan helps create a low-pressure area under the car, which is good as it will help 'suck' the car downwards. Now all we need is a high-pressure zone above to help push the car down into that low-pressure zone created by the bellypan.
Which brings us to a splitter, which performs the same task as a bellypan by creating a low-pressure zone between it's lip and the ground, sucking the car down, as well as creating a high-pressure zone above the splitter's lip where the air stagnates above the lip and against the nose of the car, pushing it down into the low-pressure zone under the lip.
what the hood vent does, is allow the air entering the radiator and some under the car, to vent to a lower pressure zone on top of the hood. (for downforce)
I'm thinking that if you're venting more air over the hood of the car and it's coming out of the vent as strongly as you say, then that extra accelerated air will cause a greater pressure drop on the top of the car, again causing the car's front-end to suck upwards more-so than before the vent in the hood was made.
On the other hand, if that air coming out of the hood-vent is relatively slow-moving with-respect-to the air already moving over the top of the hood which started at the front of the nose, then, the turbulence created by the slower-moving air-column colliding with the faster-moving air-column will cause the air to slow down, thus creating a higer pressure on top of the hood than before. This in-turn will provide more weight for the contact-patch of the front-tires, thus providing more grip in the corners and the ability to carry more speed through a corner: if one has the ***** to do-so of course.
This is very interesting; I wonder which way it's working?
01-03-2007, 12:15 PM
#22
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with the camera mounted backwards, video shows good stability up through 130mph. it produces close to 260lbs of downforce and ive been able to actually sit on the wing! no need for drag inducing biplane cables!
i used the same thickness aluminum that comes stock on a $250,000 porsche GT3 supercup car. However, because of the rear hight of the 928, i was able to keep the proportions of the wing hight the same to the supercup car, but use shorter uprights, thus making my uprights much more stiff and stable .
there is a weak link, as i have 2 grade 8 bolts holding it to the rear hatch. it could use 3. if i ever get in a spin at high speed, there is a chance it could rip off if im traveling backward. since ive only spun 1 time in 11 years of doing this, im not too worried about that. if i do get backwards, there are other things that Ill be worried about!
there is no sideways pressure on the wing end plates. it can be slight in a slide, but not enough to worry about. i had some nice oversteer that i was playing with at thunderhill. the wind didnt move, but then again, why would it. the surface area of the end plates is very small. the angle in a controled slide is also very slight usually as well.
the key thing is that im using the same grade and thickness of one the uprights of one of the best designed race cars in the world. if its good enough for the GT3,its good enough for me. (and mine are actually stiffer!)
MK
i used the same thickness aluminum that comes stock on a $250,000 porsche GT3 supercup car. However, because of the rear hight of the 928, i was able to keep the proportions of the wing hight the same to the supercup car, but use shorter uprights, thus making my uprights much more stiff and stable .
there is a weak link, as i have 2 grade 8 bolts holding it to the rear hatch. it could use 3. if i ever get in a spin at high speed, there is a chance it could rip off if im traveling backward. since ive only spun 1 time in 11 years of doing this, im not too worried about that. if i do get backwards, there are other things that Ill be worried about!
there is no sideways pressure on the wing end plates. it can be slight in a slide, but not enough to worry about. i had some nice oversteer that i was playing with at thunderhill. the wind didnt move, but then again, why would it. the surface area of the end plates is very small. the angle in a controled slide is also very slight usually as well.
the key thing is that im using the same grade and thickness of one the uprights of one of the best designed race cars in the world. if its good enough for the GT3,its good enough for me. (and mine are actually stiffer!)
MK
Originally Posted by C.F.
Mark
Your rear spoiler uprights , they look pretty thin to me, more than strong enough in the vertical plain but how about with some added sideways pressure on the end of the spoiler , how strong ? ,could it fold/collapse ?. How about some wire X bracing like on a bi-plane aircraft.
Thanks for all the detailed testing reports , I find them most interesting .
Best of luck for the upcoming season
Your rear spoiler uprights , they look pretty thin to me, more than strong enough in the vertical plain but how about with some added sideways pressure on the end of the spoiler , how strong ? ,could it fold/collapse ?. How about some wire X bracing like on a bi-plane aircraft.
Thanks for all the detailed testing reports , I find them most interesting .
Best of luck for the upcoming season
01-03-2007, 12:42 PM
#23
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Originally Posted by mark kibort
there is no sideways pressure on the wing end plates. it can be slight in a slide, but not enough to worry about. i had some nice oversteer that i was playing with at thunderhill. the wind didnt move, but then again, why would it. the surface area of the end plates is very small. the angle in a controled slide is also very slight usually as well.
the key thing is that im using the same grade and thickness of one the uprights of one of the best designed race cars in the world. if its good enough for the GT3,its good enough for me. (and mine are actually stiffer!)
MK
the key thing is that im using the same grade and thickness of one the uprights of one of the best designed race cars in the world. if its good enough for the GT3,its good enough for me. (and mine are actually stiffer!)
MK
Like you say, if its good enough for a GT3 it should just about be good enough for a superior car like the 928
01-03-2007, 12:42 PM
#24
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Thread Starter
see my inserts >>>>>>
I saw a great article on this, and i cant find it. but it goes over all these points in detail. Ill see if i can dig it up. do a search on aerodyamic splittlers - Downforce, etc, and you can probably verify the reasons for my design.
Originally Posted by SwayBar
Mark, I think you have it backwards.
Having a bellypan on the car forces the air to go between it and the ground, causing that air to accelerate relative to 'ambient'; as a result, a low-pressure zone is created.
>>>>>only if the opening of the air entering the front of the car is larger than the area under the engine, which is it constant. the goal is to have the air going under the car to be at ambient. from the wind tunnel tests, you can see that the under car air is at ambient. the belly pans and all the underbody pans are for drag reduction under the car. at the speeds i race at, im not too worried about it. in fact, when racing a 360challenge car, with extensive belly and underbody pannels and diffusers, i had no problem keeping up!
Assuming the pressure under the hood is higher, the higher-pressure air under the hood it will then 'vent' into the lower pressure area under the bellypan via the bellypan's holes, thus allowing more flow through the radiator.
>>>>>>yes, and this is what happens and is the reason for the belly pan vents. exactly right
So a bellypan helps create a low-pressure area under the car, which is good as it will help 'suck' the car downwards. Now all we need is a high-pressure zone above to help push the car down into that low-pressure zone created by the bellypan.
>>>>> the belly pan doesnt create a lower pressure zone under the car.
we are talking about relative pressure here. ambient is under the car, on top of the hood is accelerated car due to the distance difference between under the car vs the air traveling over the car. the faster the air has to go to travel the same distance, the lower the pressure. The belly pan does create a smoother air flow under the car that reduces drag somewhat and keeps things much cleaner under there.
Which brings us to a splitter, which performs the same task as a bellypan by creating a low-pressure zone between it's lip and the ground, sucking the car down, as well as creating a high-pressure zone above the splitter's lip where the air stagnates above the lip and against the nose of the car, pushing it down into the low-pressure zone under the lip.
>>>>>>>>No, the highest pressure zone is the nose. the air pressure at the nose starts to roll off to go under the car, where it meets the splitter the splitter channels the air to the sides where it is vented. winglets on cars can even force this directed air to the sides of the car, where that air will meet the wider-than-body rear wings for added rear downforce as well. Lift is more than differential pressure, its change of momentum as well. there is no change of momentum due to the splitter like the rear wing. think of the splitter as a channel for the higher pressure zone to vent to the sides rather than travelling underneath the car creating more molecules to be forced under the car, increasing lift under the car. (or better said raising the ambient pressure under the car, and changing the differential pressure ).
You are correct that the air above the hood is at a lower pressure. But that lower pressure is due to the air accelerating over the hood's curved surface which has the same affect as the bellypan: it creates a low-pressure zone which causes the car to 'suck' upwards into the low pressure zone, exactly the opposite of what one wants on a high-speed track.
>>>>>actually the reason for the hood lower pressure zone is the distance the air has to travel vs the air underneath the car.
I'm thinking that if you're venting more air over the hood of the car and it's coming out of the vent as strongly as you say, then that extra accelerated air will cause a greater pressure drop on the top of the car, again causing the car's front-end to suck upwards more-so than before the vent in the hood was made.
>>>>>>>just the opposite. you are confusing the effect of diffusers. what is happening is that the ambient air pressure under the car and in the engine compartment will move to differential pressure. if the pressure is lower on top of the car than the bottom, it will try and vent in that direction. the less air molecules that go under the car vs on to of the car, will create downforce. the engine air fed from the radiator inlet, which is a good sized area, enters the engine compartement. it has to go somewhere. underneath the car increases the under the car pressure. if it can go over the car it helps two ways. the pressure isnt raised under the car (creating lift) and the air goes over the car lowering the already lower pressure on top of the wing, raising the pressure in the low pressure zone on the hood, creating downforce!
On the other hand, if that air coming out of the hood-vent is relatively slow-moving with-respect-to the air already moving over the top of the hood which started at the front of the nose, then, the turbulence created by the slower-moving air-column colliding with the faster-moving air-column will cause the air to slow down, thus creating a higer pressure on top of the hood than before. This in-turn will provide more weight for the contact-patch of the front-tires, thus providing more grip in the corners and the ability to carry more speed through a corner: if one has the ***** to do-so of course.
>>>>>>this is what is happening. this is also the reason for front diffusers. if i was able to make channels for the air entering the car's nose and slow it down. have a big channel feeding an even LARGER channel at the exit on the hood, the air would slow down and that would create even higher pressure changes on top of the hood. this same technique is used in rear channel diffusers.
This is very interesting; I wonder which way it's working?
Having a bellypan on the car forces the air to go between it and the ground, causing that air to accelerate relative to 'ambient'; as a result, a low-pressure zone is created.
>>>>>only if the opening of the air entering the front of the car is larger than the area under the engine, which is it constant. the goal is to have the air going under the car to be at ambient. from the wind tunnel tests, you can see that the under car air is at ambient. the belly pans and all the underbody pans are for drag reduction under the car. at the speeds i race at, im not too worried about it. in fact, when racing a 360challenge car, with extensive belly and underbody pannels and diffusers, i had no problem keeping up!
Assuming the pressure under the hood is higher, the higher-pressure air under the hood it will then 'vent' into the lower pressure area under the bellypan via the bellypan's holes, thus allowing more flow through the radiator.
>>>>>>yes, and this is what happens and is the reason for the belly pan vents. exactly right
So a bellypan helps create a low-pressure area under the car, which is good as it will help 'suck' the car downwards. Now all we need is a high-pressure zone above to help push the car down into that low-pressure zone created by the bellypan.
>>>>> the belly pan doesnt create a lower pressure zone under the car.
we are talking about relative pressure here. ambient is under the car, on top of the hood is accelerated car due to the distance difference between under the car vs the air traveling over the car. the faster the air has to go to travel the same distance, the lower the pressure. The belly pan does create a smoother air flow under the car that reduces drag somewhat and keeps things much cleaner under there.
Which brings us to a splitter, which performs the same task as a bellypan by creating a low-pressure zone between it's lip and the ground, sucking the car down, as well as creating a high-pressure zone above the splitter's lip where the air stagnates above the lip and against the nose of the car, pushing it down into the low-pressure zone under the lip.
>>>>>>>>No, the highest pressure zone is the nose. the air pressure at the nose starts to roll off to go under the car, where it meets the splitter the splitter channels the air to the sides where it is vented. winglets on cars can even force this directed air to the sides of the car, where that air will meet the wider-than-body rear wings for added rear downforce as well. Lift is more than differential pressure, its change of momentum as well. there is no change of momentum due to the splitter like the rear wing. think of the splitter as a channel for the higher pressure zone to vent to the sides rather than travelling underneath the car creating more molecules to be forced under the car, increasing lift under the car. (or better said raising the ambient pressure under the car, and changing the differential pressure ).
You are correct that the air above the hood is at a lower pressure. But that lower pressure is due to the air accelerating over the hood's curved surface which has the same affect as the bellypan: it creates a low-pressure zone which causes the car to 'suck' upwards into the low pressure zone, exactly the opposite of what one wants on a high-speed track.
>>>>>actually the reason for the hood lower pressure zone is the distance the air has to travel vs the air underneath the car.
I'm thinking that if you're venting more air over the hood of the car and it's coming out of the vent as strongly as you say, then that extra accelerated air will cause a greater pressure drop on the top of the car, again causing the car's front-end to suck upwards more-so than before the vent in the hood was made.
>>>>>>>just the opposite. you are confusing the effect of diffusers. what is happening is that the ambient air pressure under the car and in the engine compartment will move to differential pressure. if the pressure is lower on top of the car than the bottom, it will try and vent in that direction. the less air molecules that go under the car vs on to of the car, will create downforce. the engine air fed from the radiator inlet, which is a good sized area, enters the engine compartement. it has to go somewhere. underneath the car increases the under the car pressure. if it can go over the car it helps two ways. the pressure isnt raised under the car (creating lift) and the air goes over the car lowering the already lower pressure on top of the wing, raising the pressure in the low pressure zone on the hood, creating downforce!
On the other hand, if that air coming out of the hood-vent is relatively slow-moving with-respect-to the air already moving over the top of the hood which started at the front of the nose, then, the turbulence created by the slower-moving air-column colliding with the faster-moving air-column will cause the air to slow down, thus creating a higer pressure on top of the hood than before. This in-turn will provide more weight for the contact-patch of the front-tires, thus providing more grip in the corners and the ability to carry more speed through a corner: if one has the ***** to do-so of course.
>>>>>>this is what is happening. this is also the reason for front diffusers. if i was able to make channels for the air entering the car's nose and slow it down. have a big channel feeding an even LARGER channel at the exit on the hood, the air would slow down and that would create even higher pressure changes on top of the hood. this same technique is used in rear channel diffusers.
This is very interesting; I wonder which way it's working?
01-03-2007, 02:21 PM
#25
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Thread Starter
http://e30m3performance.com/installs...vent/index.htm
this isnt the article i was looking at, but just stumbled upon it today. the article i was looking for was from some aero engineers masters thesis.
mk
this isnt the article i was looking at, but just stumbled upon it today. the article i was looking for was from some aero engineers masters thesis.
mk
01-03-2007, 02:42 PM
#26
Rennlist Member
Originally Posted by C.F.
Steve
drnick with the orange car here in the UK has some ,IIRC they are 996 modified to fit (maybe modified then a mold taken ), best pick I could find is on this thread
https://rennlist.com/forums/showthread.
drnick with the orange car here in the UK has some ,IIRC they are 996 modified to fit (maybe modified then a mold taken ), best pick I could find is on this thread
https://rennlist.com/forums/showthread.
You can buy them at Demon Tweeks relatively cheaply...Alex
01-03-2007, 03:13 PM
#27
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Originally Posted by Cheburator
Wrong... The sideskirts are off a Vauxhall Vectra body kit... Modified using a hacksaw You can buy them at Demon Tweeks relatively cheaply...
Alex
You can buy them at Demon Tweeks relatively cheaply...Alex
01-03-2007, 04:55 PM
#28
Instructor
Hi guys, great thread on this areodynamic talk about our cars. Seems like you do and have done alot of technical testing on your cars to go fast, it's interesting reading.
I have one question. My 1981 928 has 'S' front and rear spoilers fitted but I have no belly pan under the engine fitted. It could have been damaged by the PO I'm not sure. So how much does that effect what we are talking about with regards to front downforce etc?
Thanks for the read
Glenn.
'81 928 (Australian Build)
I have one question. My 1981 928 has 'S' front and rear spoilers fitted but I have no belly pan under the engine fitted. It could have been damaged by the PO I'm not sure. So how much does that effect what we are talking about with regards to front downforce etc?
Thanks for the read
Glenn.
'81 928 (Australian Build)
01-03-2007, 11:58 PM
#29
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Thread Starter
the underbody pans are really for keeping the engine clean, as well as cleaning the air flow under the car for less drag. the drag amounts are not going to be much anyway. however, if the entire underbody is pann'ed, and a diffuser is used , there can be more downforce overall created. no 928 is at this level of developement, and for good reason, its not worth it. our cars even in their most racey form, dont go fast enough to really benefit from underbody panels.
a big splitter and wing is really all that is needed. on a stock car however, like a viper or a lambo without wings and splitters, its a helps a lot.
mk
a big splitter and wing is really all that is needed. on a stock car however, like a viper or a lambo without wings and splitters, its a helps a lot.
mk
Originally Posted by GRTWHT
Hi guys, great thread on this areodynamic talk about our cars. Seems like you do and have done alot of technical testing on your cars to go fast, it's interesting reading.
I have one question. My 1981 928 has 'S' front and rear spoilers fitted but I have no belly pan under the engine fitted. It could have been damaged by the PO I'm not sure. So how much does that effect what we are talking about with regards to front downforce etc?
Thanks for the read
Glenn.
'81 928 (Australian Build)
I have one question. My 1981 928 has 'S' front and rear spoilers fitted but I have no belly pan under the engine fitted. It could have been damaged by the PO I'm not sure. So how much does that effect what we are talking about with regards to front downforce etc?
Thanks for the read
Glenn.
'81 928 (Australian Build)
01-08-2007, 04:11 AM
#30
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Thread Starter
Just posted the 2:01.xx lap with the SSF M3 during this SCCA Thunderhill free test day. you cand see the effects of the splitter and hood vent, as well as the lower wing setting. the car is very well hooked up now!
http://www.youtube.com/watch?v=kj2wN2BrFjs
Mk
http://www.youtube.com/watch?v=kj2wN2BrFjs
Mk