Any reason not to vent the radiators into the wheel wells (said by Pelican to reduce
01-01-2017, 07:56 PM
#31
interesting concepts and valid observations about aero being tricky etc but there are some things that are givens and constants and fundamentals. I spent a career designing and manufacturing ( and racing ) prototypes and spent more than a little time in wind tunnels both full and scale. none of that allows me to answer this question with authority but I can shed some factual light on some of the issues raised so far...
1) in order to get flow you need a pressure differential... if the pressures are the same on both sides then the air is stagnant. if its not the same it will flow from the hi press side to the low press side. why is that important here ? simple... a rotating wheel inside a fender makes that area a hi pressure area... how hi ? don't know BUT if its higher or approaching the pressure on the exit of the rad then you aren't helping anything at all and , in fact, may be making it worse. how can you tell ? simple... pressure taps and a good data system. you put taps all over the place and map the pressures as they actually exist in the real world. I spent a lot of time venting and creating extractors for the wheel wells to get those pressures down. that's why every prototype you see has vents on the top of the front wheel arches and the rear sides of the bodywork cut back as far as the rules allow.
2) will a tunnel tell you this ? probably not unless its a VERY good rolling road tunnel and even at that , that data is static and what happens at various speeds and attitudes is often VERY much different
3) downforce and drag... maybe and maybe not but you aren't going to do something like this and " feel " some massive improvement. can you see it on the stop watch ? maybe... IF you are a professional and using a good solid repeatable engineering test regime where you establish proper base lines and sequencing and a very good high sample rate data system. . I have spent thousands and thousands of hours testing and even the smallest gains are mind numbingly difficult to accurately quantify and aero are the worst. what you are talking about here is very very subtle... not like bolting some giant honking wing on the back that makes 800 lbs of df at 30 mph or something...
4) is it real or imagined ? another good question. lets say you are a top level track guy. can run at or under the lap record all the time and win most of the races you enter... fine... so make the car stock and go do 5 laps as fast as you can on a new set of control tires. now put on a second set of new control tires and repeat. are the lap times inside of the same two tenths all 5 laps ? if so, great ... now make your aero change ( which you have pre configured ) put the original set of tires back on and do a new 5 laps . same, better or worse on the watch ? repeat with the second set of control tires... then do it all again. back to back... same fuel loads, alternating setups and tires. in the end after 50 laps or so the pattern will be crystal clear. you throw out the highs and lows and average the rest and that is your answer. sound like a lot of expensive work ? youre right... it is. but like all things you either know the truth or you are guessing.
5) can you measure down force ? sure . strain gages or shock pots. strain gages if you have push or pull rods or shock pots to measure deflection at speed.
the bottom line is that all your questions have knowable and quantifiable answers if you are willing to do the work. everything else is just guesswork , voodoo and mythology.
as for this specific question... from what I know and understand I can't imagine that venting the rads into the wheel wells is worth anything at all unless two things are true... one, that porshe made a pretty bad mistake about their rad exit ducting ( which I would be pretty surprised at since the EXIT ducting is twice as important as the inlet ducting ) and two that you have done something to get the air out of the wheel wells themselves in addition to all else. just packing more air in there will just make lift which is not what you want. but , again, like all things aero I could be completely wrong. aero is one of those things that you can theorize to death only to discover that , in the real world at speed, something else you never thought of actually happens.
1) in order to get flow you need a pressure differential... if the pressures are the same on both sides then the air is stagnant. if its not the same it will flow from the hi press side to the low press side. why is that important here ? simple... a rotating wheel inside a fender makes that area a hi pressure area... how hi ? don't know BUT if its higher or approaching the pressure on the exit of the rad then you aren't helping anything at all and , in fact, may be making it worse. how can you tell ? simple... pressure taps and a good data system. you put taps all over the place and map the pressures as they actually exist in the real world. I spent a lot of time venting and creating extractors for the wheel wells to get those pressures down. that's why every prototype you see has vents on the top of the front wheel arches and the rear sides of the bodywork cut back as far as the rules allow.
2) will a tunnel tell you this ? probably not unless its a VERY good rolling road tunnel and even at that , that data is static and what happens at various speeds and attitudes is often VERY much different
3) downforce and drag... maybe and maybe not but you aren't going to do something like this and " feel " some massive improvement. can you see it on the stop watch ? maybe... IF you are a professional and using a good solid repeatable engineering test regime where you establish proper base lines and sequencing and a very good high sample rate data system. . I have spent thousands and thousands of hours testing and even the smallest gains are mind numbingly difficult to accurately quantify and aero are the worst. what you are talking about here is very very subtle... not like bolting some giant honking wing on the back that makes 800 lbs of df at 30 mph or something...
4) is it real or imagined ? another good question. lets say you are a top level track guy. can run at or under the lap record all the time and win most of the races you enter... fine... so make the car stock and go do 5 laps as fast as you can on a new set of control tires. now put on a second set of new control tires and repeat. are the lap times inside of the same two tenths all 5 laps ? if so, great ... now make your aero change ( which you have pre configured ) put the original set of tires back on and do a new 5 laps . same, better or worse on the watch ? repeat with the second set of control tires... then do it all again. back to back... same fuel loads, alternating setups and tires. in the end after 50 laps or so the pattern will be crystal clear. you throw out the highs and lows and average the rest and that is your answer. sound like a lot of expensive work ? youre right... it is. but like all things you either know the truth or you are guessing.
5) can you measure down force ? sure . strain gages or shock pots. strain gages if you have push or pull rods or shock pots to measure deflection at speed.
the bottom line is that all your questions have knowable and quantifiable answers if you are willing to do the work. everything else is just guesswork , voodoo and mythology.
as for this specific question... from what I know and understand I can't imagine that venting the rads into the wheel wells is worth anything at all unless two things are true... one, that porshe made a pretty bad mistake about their rad exit ducting ( which I would be pretty surprised at since the EXIT ducting is twice as important as the inlet ducting ) and two that you have done something to get the air out of the wheel wells themselves in addition to all else. just packing more air in there will just make lift which is not what you want. but , again, like all things aero I could be completely wrong. aero is one of those things that you can theorize to death only to discover that , in the real world at speed, something else you never thought of actually happens.
01-01-2017, 09:28 PM
#32
Burning Brakes
interesting concepts and valid observations about aero being tricky etc but there are some things that are givens and constants and fundamentals. I spent a career designing and manufacturing ( and racing ) prototypes and spent more than a little time in wind tunnels both full and scale. none of that allows me to answer this question with authority but I can shed some factual light on some of the issues raised so far...
1) in order to get flow you need a pressure differential... if the pressures are the same on both sides then the air is stagnant. if its not the same it will flow from the hi press side to the low press side. why is that important here ? simple... a rotating wheel inside a fender makes that area a hi pressure area... how hi ? don't know BUT if its higher or approaching the pressure on the exit of the rad then you aren't helping anything at all and , in fact, may be making it worse. how can you tell ? simple... pressure taps and a good data system. you put taps all over the place and map the pressures as they actually exist in the real world. I spent a lot of time venting and creating extractors for the wheel wells to get those pressures down. that's why every prototype you see has vents on the top of the front wheel arches and the rear sides of the bodywork cut back as far as the rules allow.
2) will a tunnel tell you this ? probably not unless its a VERY good rolling road tunnel and even at that , that data is static and what happens at various speeds and attitudes is often VERY much different
3) downforce and drag... maybe and maybe not but you aren't going to do something like this and " feel " some massive improvement. can you see it on the stop watch ? maybe... IF you are a professional and using a good solid repeatable engineering test regime where you establish proper base lines and sequencing and a very good high sample rate data system. . I have spent thousands and thousands of hours testing and even the smallest gains are mind numbingly difficult to accurately quantify and aero are the worst. what you are talking about here is very very subtle... not like bolting some giant honking wing on the back that makes 800 lbs of df at 30 mph or something...
4) is it real or imagined ? another good question. lets say you are a top level track guy. can run at or under the lap record all the time and win most of the races you enter... fine... so make the car stock and go do 5 laps as fast as you can on a new set of control tires. now put on a second set of new control tires and repeat. are the lap times inside of the same two tenths all 5 laps ? if so, great ... now make your aero change ( which you have pre configured ) put the original set of tires back on and do a new 5 laps . same, better or worse on the watch ? repeat with the second set of control tires... then do it all again. back to back... same fuel loads, alternating setups and tires. in the end after 50 laps or so the pattern will be crystal clear. you throw out the highs and lows and average the rest and that is your answer. sound like a lot of expensive work ? youre right... it is. but like all things you either know the truth or you are guessing.
5) can you measure down force ? sure . strain gages or shock pots. strain gages if you have push or pull rods or shock pots to measure deflection at speed.
the bottom line is that all your questions have knowable and quantifiable answers if you are willing to do the work. everything else is just guesswork , voodoo and mythology.
as for this specific question... from what I know and understand I can't imagine that venting the rads into the wheel wells is worth anything at all unless two things are true... one, that porshe made a pretty bad mistake about their rad exit ducting ( which I would be pretty surprised at since the EXIT ducting is twice as important as the inlet ducting ) and two that you have done something to get the air out of the wheel wells themselves in addition to all else. just packing more air in there will just make lift which is not what you want. but , again, like all things aero I could be completely wrong. aero is one of those things that you can theorize to death only to discover that , in the real world at speed, something else you never thought of actually happens.
1) in order to get flow you need a pressure differential... if the pressures are the same on both sides then the air is stagnant. if its not the same it will flow from the hi press side to the low press side. why is that important here ? simple... a rotating wheel inside a fender makes that area a hi pressure area... how hi ? don't know BUT if its higher or approaching the pressure on the exit of the rad then you aren't helping anything at all and , in fact, may be making it worse. how can you tell ? simple... pressure taps and a good data system. you put taps all over the place and map the pressures as they actually exist in the real world. I spent a lot of time venting and creating extractors for the wheel wells to get those pressures down. that's why every prototype you see has vents on the top of the front wheel arches and the rear sides of the bodywork cut back as far as the rules allow.
2) will a tunnel tell you this ? probably not unless its a VERY good rolling road tunnel and even at that , that data is static and what happens at various speeds and attitudes is often VERY much different
3) downforce and drag... maybe and maybe not but you aren't going to do something like this and " feel " some massive improvement. can you see it on the stop watch ? maybe... IF you are a professional and using a good solid repeatable engineering test regime where you establish proper base lines and sequencing and a very good high sample rate data system. . I have spent thousands and thousands of hours testing and even the smallest gains are mind numbingly difficult to accurately quantify and aero are the worst. what you are talking about here is very very subtle... not like bolting some giant honking wing on the back that makes 800 lbs of df at 30 mph or something...
4) is it real or imagined ? another good question. lets say you are a top level track guy. can run at or under the lap record all the time and win most of the races you enter... fine... so make the car stock and go do 5 laps as fast as you can on a new set of control tires. now put on a second set of new control tires and repeat. are the lap times inside of the same two tenths all 5 laps ? if so, great ... now make your aero change ( which you have pre configured ) put the original set of tires back on and do a new 5 laps . same, better or worse on the watch ? repeat with the second set of control tires... then do it all again. back to back... same fuel loads, alternating setups and tires. in the end after 50 laps or so the pattern will be crystal clear. you throw out the highs and lows and average the rest and that is your answer. sound like a lot of expensive work ? youre right... it is. but like all things you either know the truth or you are guessing.
5) can you measure down force ? sure . strain gages or shock pots. strain gages if you have push or pull rods or shock pots to measure deflection at speed.
the bottom line is that all your questions have knowable and quantifiable answers if you are willing to do the work. everything else is just guesswork , voodoo and mythology.
as for this specific question... from what I know and understand I can't imagine that venting the rads into the wheel wells is worth anything at all unless two things are true... one, that porshe made a pretty bad mistake about their rad exit ducting ( which I would be pretty surprised at since the EXIT ducting is twice as important as the inlet ducting ) and two that you have done something to get the air out of the wheel wells themselves in addition to all else. just packing more air in there will just make lift which is not what you want. but , again, like all things aero I could be completely wrong. aero is one of those things that you can theorize to death only to discover that , in the real world at speed, something else you never thought of actually happens.
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Leedlast (01-24-2024)
01-01-2017, 11:25 PM
#33
My gt3 vents to the wheels well. My old 996 didn't. I added the vents and brake scoops behind the rotors. No aero issues and cooler brakes.
https://rennlist.com/forums/996-forum/495438-track-doods-brake-cooling-mod-pics.html
-td
https://rennlist.com/forums/996-forum/495438-track-doods-brake-cooling-mod-pics.html
-td
01-02-2017, 05:40 AM
#34
that's possible but I would ask the usual questions.... first , how do you know ? is this empirical objective data generated by instrumentation and testing or " seat of the pants " ? and I would wonder if the gt3 is configured differently from the factory both in a structural or set up sense. as an example I would start with the obvious that aero is a full concept. there are no single magic beans that suddenly transform a car. its a dozen small things to manage the pressures and flows to generate the differential pressures to make them do what you want. if the gt3 exits into the fender wells when the carerra does not then I am absolutely certain that porsche did a boatload of other small but significant things at the same time to deal with the new profile and get the air to go where they wanted and do what they wanted it to do. these are VERY smart guys and not prone to stupid mistakes. and second I would point out that aero effect is a direct and absolute function of mechanical set up. lets use something simple as example ... ride height . lets say you have a car that makes 1500 lbs of downforce at 125 mph due to an sophisticated underbody. why does that work ? because the air moves faster along the bottom surface than it does across the top surface and exploits bernuelli's principle effectively. now... what happens to that car when you lower the from ride height too much and shut off that underbody flow ? or raise it too much and destroy the effectiveness of the underbody design ? instant loss of a huge percentage of your downforce. aero is like that. even if your theory, interpretation, design and execution are all correct, the basic setup of the car in a mechanical sense has everything to do with whether or not your results will be right wrong or indifferent. I can appreciate that people love screwing around with their cars and cutting them up and changing things. that's a lot of the joy of the game but in the end there are a couple of fundamental truths that always emerge... the first is that the better you make your car for the race track, the worse you are making it for the street. for instance brakes that work brilliantly on your track days at sebring will feel numb and be ineffective when cold on the street. those track springs , bars and shocks that keep the car nice and flat on the track , make the car terrible in the wet on rt 95 going to work the rest of the time... and second... when it comes to aero it is exactly like dealing with with women... there are only two ways to understand it ... and nobody knows either of them.
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01-02-2017, 07:50 AM
#35
Rennlist Member
Brilliant quote!
01-02-2017, 06:49 PM
#37
https://rennlist.com/forums/996-gt2-...eflectors.html
Someone mentioned using the 996 part on his 996 Carrera, but didn't say more. One has to wonder if this does not require additional GT3 pieces, for instance the wheel well piece in the photo above.
Here are the part numbers, left and right: 99657523130 and 99657523230.
Why did they do it this way on the 996.2 GT3 instead of the Turbo way? Possibly because they knew better (the MkII GT3 is the newer car). Or possibly because all they cared about on the GT3 was keeping the brakes cool, whereas on the Turbo they had different objectives. There's no mention in the thread of aero benefits, but there is of brake cooling, so if the GT3 guys understand correctly, these are designed to do that, and probably do it better than the Turbo wheelwell vents. But how this systems impacts drag and lift is unclear. Porsche may have sacrificed all for cool brakes. Still, it does seem that venting air into wheel wells on cars with bumpers like ours isn't a disaster, or else Porsche wouldn't have done it on the 996.2 GT3.
Last edited by rs10; 01-03-2017 at 05:44 PM.
01-02-2017, 07:40 PM
#38
Rennlist Member
Originally Posted by rs10
. But how this systems impacts drag and lift is unclear. Porsche may have sacrificed all for cool brakes. Still, it does seem that venting air into wheel wells on cars with bumpers like ours isn't a disaster, or else Porsche wouldn't have done it on the 996.2 GT3.
01-02-2017, 08:22 PM
#39
So I found out how this was done here:
https://rennlist.com/forums/996-foru...-mod-pics.html
Well, I sort of found out. The guy who did it seems sure you can do it without a GT3 liner, but it's not clear whether he actually tried it or just used a GT3 liner ... .
The other interesting note is that this interferes with full lock when he uses 245s on 8.5s, but not on the street with 8s (tire width uspecified, presumably 225). So for people running 245s on track, this can be an issue. (You may not need to turn that tight, but you may need to catch a spin ... .)
https://rennlist.com/forums/996-foru...-mod-pics.html
Well, I sort of found out. The guy who did it seems sure you can do it without a GT3 liner, but it's not clear whether he actually tried it or just used a GT3 liner ... .
The other interesting note is that this interferes with full lock when he uses 245s on 8.5s, but not on the street with 8s (tire width uspecified, presumably 225). So for people running 245s on track, this can be an issue. (You may not need to turn that tight, but you may need to catch a spin ... .)
01-02-2017, 08:27 PM
#40
No, not at all, hence being my concern that what's ideal for a GT3 isn't ideal for me. Occasional track use, but I'm much more interested in how it works on the street. I'm looking for a way to get the front lift down to somewhere between C4S and GT3 levels with minimal drag impact, and that won't get banged up as much as a GT3/aerokit bumper would where I drive (and park). If there's a solution that reduces drag and cools the brakes, even better.
01-02-2017, 09:13 PM
#41
Attached is a pic of the "infamous" fender well louvers on my 4S.
Question: Wondering why you are concerned about lift and drag on the street?? Your speed limits must be higher than my area!
Yes, for the anti-pumpkin crowd...those are pumpkins so just call me a "loser" and be done with it!
Question: Wondering why you are concerned about lift and drag on the street?? Your speed limits must be higher than my area!
Yes, for the anti-pumpkin crowd...those are pumpkins so just call me a "loser" and be done with it!
01-02-2017, 10:25 PM
#42
Shameful Thread Killer
Rennlist Member
Rennlist Member
More sauce for the goose. As the 928 was to be a 'clean sheet' design, it spent a fair amount of time in the wind tunnel. Come to find out, Hanz or Franz was having some fun and put it in backward one day then discovered that it had a better Cd going backward than forward. As the power and speed crept up with bigger engines, by the time the S4 came along, at speeds over about 145, the tail was starting to lift some. Hence the 87 and later 928s ALL came with the now infamous beer shelf back there.
Not to be outdone, Lamborghini fitted a ginormous wing to the Countach in version 2 or 3(can't recall). It had the effect of slowing the car down about 6-8MPH at top end, and provided less than 30Lbs of downforce to the back of the car. Looked absolutely fabulous, was counterproductive. But - 80% of the people who ordered a Countach got one with the massive wing.
http://motoburg.com/images/lamborghi...lp5000s-06.jpg
countach five-zero-zero-zero, make left traffic, follow the VW beetle at nine o'clock, 3 miles. Descend to 2000 and make your speed one-four-zero.
Not to be outdone, Lamborghini fitted a ginormous wing to the Countach in version 2 or 3(can't recall). It had the effect of slowing the car down about 6-8MPH at top end, and provided less than 30Lbs of downforce to the back of the car. Looked absolutely fabulous, was counterproductive. But - 80% of the people who ordered a Countach got one with the massive wing.
http://motoburg.com/images/lamborghi...lp5000s-06.jpg
countach five-zero-zero-zero, make left traffic, follow the VW beetle at nine o'clock, 3 miles. Descend to 2000 and make your speed one-four-zero.
01-02-2017, 10:37 PM
#43
So I found out how this was done here:
https://rennlist.com/forums/996-foru...-mod-pics.html
Well, I sort of found out. The guy who did it seems sure you can do it without a GT3 liner, but it's not clear whether he actually tried it or just used a GT3 liner ... .
The other interesting note is that this interferes with full lock when he uses 245s on 8.5s, but not on the street with 8s (tire width uspecified, presumably 225). So for people running 245s on track, this can be an issue. (You may not need to turn that tight, but you may need to catch a spin ... .)
https://rennlist.com/forums/996-foru...-mod-pics.html
Well, I sort of found out. The guy who did it seems sure you can do it without a GT3 liner, but it's not clear whether he actually tried it or just used a GT3 liner ... .
The other interesting note is that this interferes with full lock when he uses 245s on 8.5s, but not on the street with 8s (tire width uspecified, presumably 225). So for people running 245s on track, this can be an issue. (You may not need to turn that tight, but you may need to catch a spin ... .)
I ran that configuration for a couple years. Mostly track duty. I can post more info if anyone needs it.
-td
01-03-2017, 02:16 AM
#44
Rennlist Member
^^ this looks fine though I highly doubt it will have any effect on street driving.
FYI, while we are on the subject, I did fit some GT2 brake ducts on my C2 briefly and it was quite humorous. It significantly increased airflow to the area right below my rotor, which would be relevant if I had GT2 sized rotors.
FYI, while we are on the subject, I did fit some GT2 brake ducts on my C2 briefly and it was quite humorous. It significantly increased airflow to the area right below my rotor, which would be relevant if I had GT2 sized rotors.
01-03-2017, 05:30 PM
#45
Om the other hand, driving today on cold damp roads with strong winds, at speeds such that you might get away with a warning in your area, with 205 front winter tires, I would have appreciated a front end that was more tied down.
Thanks for the picture!
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wdb (06-20-2022)