Downforce?
07-24-2007, 02:35 PM
#1
Race Director
Thread Starter
Downforce?
Would anyone know how much if any of the air that goes over the windshield, goes off to the sides? I have been doing some testing and it seems that the drivers side has more air that goes to the side rather then over the car. I have been using streamers taped to the edge of the hood.
If anyone has found this before and fixed it, I'd like to know.
Also, does having the vent or heat on create less downforce as air is sucked into the cowl and down into the cabin rather then going over the car?
I am testing this on my '88. Would taking the underhood lights out and using those as air scoops create more downforce? Holes would need to be drilled in the hood shroud at the base of the windshield. The hood lights would let air go up over the car rather then out to the sides, it would normally escape by the wheels.
If anyone has found this before and fixed it, I'd like to know.
Also, does having the vent or heat on create less downforce as air is sucked into the cowl and down into the cabin rather then going over the car?
I am testing this on my '88. Would taking the underhood lights out and using those as air scoops create more downforce? Holes would need to be drilled in the hood shroud at the base of the windshield. The hood lights would let air go up over the car rather then out to the sides, it would normally escape by the wheels.
07-24-2007, 02:41 PM
#2
Race Director
I would say a considerable amount of air spills over the sides of the winshield, but I have no idea how much lift this generates. A simple piece of aluminum channel up each side of the winshield (gurney) would decrease it greatly.
As for the hood, make sure you are far enough forward, as there is actually a high pressure area around the cowl. You need louvers on the upper surface, as well as a lower pressure area, to actually evacuate any air.
I don't think the HVAC draws enough air to make a measurable difference, but I have no data.
As for the hood, make sure you are far enough forward, as there is actually a high pressure area around the cowl. You need louvers on the upper surface, as well as a lower pressure area, to actually evacuate any air.
I don't think the HVAC draws enough air to make a measurable difference, but I have no data.
07-24-2007, 03:24 PM
#3
Race Director
Thread Starter
OK thanks, that is good to know that there is spillage to the sides of the windshield.
I am trying some hood mods and they have helped with heat but I do not want to lose downforce.
My first mod was to cut the cowl seal, I have read here that this is a bad idea as it can cost you downforce. But, next I removed the underhood lights. On the C4 these are pretty big scoops right above the headers. Air that goes in those then comes out four 5/8" holes cut through the hood liner at the base of the windshield by where the cowl seal is cut. My thought was that forcing more air out there would negate the cowl seal mods loss in downforce.
I have tested the car like this and it seems to be doing well. I am thinking I need a more accurate way to measure this then streamers though. My car sees use as a road course car, drag, and street, so I don't want to add aluminum channel till the car is a dedicaded track car.
Right now the car runs cooler and the streamers mostly go up. I do find it odd that the drivers side streamers go to the sides more then the passenger side. The passenger side has areas where the streamers go up over the windshield very well and one area where it goes to the side toward the mirror.
Has anyone else done both of these mods? It's free and easy to do and really helps with heat. I could tape the sections off if there is a loss in downforce when I go to a high speed event.
I am trying some hood mods and they have helped with heat but I do not want to lose downforce.
My first mod was to cut the cowl seal, I have read here that this is a bad idea as it can cost you downforce. But, next I removed the underhood lights. On the C4 these are pretty big scoops right above the headers. Air that goes in those then comes out four 5/8" holes cut through the hood liner at the base of the windshield by where the cowl seal is cut. My thought was that forcing more air out there would negate the cowl seal mods loss in downforce.
I have tested the car like this and it seems to be doing well. I am thinking I need a more accurate way to measure this then streamers though. My car sees use as a road course car, drag, and street, so I don't want to add aluminum channel till the car is a dedicaded track car.
Right now the car runs cooler and the streamers mostly go up. I do find it odd that the drivers side streamers go to the sides more then the passenger side. The passenger side has areas where the streamers go up over the windshield very well and one area where it goes to the side toward the mirror.
Has anyone else done both of these mods? It's free and easy to do and really helps with heat. I could tape the sections off if there is a loss in downforce when I go to a high speed event.
07-24-2007, 04:50 PM
#4
Melting Slicks
No offense, but why are you so concerned with these mi-nute little things...right now anyway??
You said you use your car for both street and track, etc. There are a thousand ways to get speed, handling, downforce, etc. than to be concerning yourself about whether air spills over the front windshield....streamers, and whatever else you've done....and may be losing sleep over.
I see all these things about your car: '88 Corvette: coupe, Z52, auto, 3.07, A/O intake, K&N, free mods, ported plenum, TPIS big mouth base, AS&M runners. Brake ducts, C5 calipers, Carbotech pads. Lowered, C5 silver thin spokes four 18x9.5".
But I see nothing about good sway bars or other suspension tweaks. The fact that you've "lowered" the car may very well mean you have now really screwed up the handling and probably changed the rake and angle of the car (which then makes your streamers go in funny directions). I hate it when that happens.
Stick with the big stuff my friend - seat time, suspension alignment and proper tuning, tires, brakes, seat time, tires, brakes, repeat as often as necessary.
You said you use your car for both street and track, etc. There are a thousand ways to get speed, handling, downforce, etc. than to be concerning yourself about whether air spills over the front windshield....streamers, and whatever else you've done....and may be losing sleep over.
I see all these things about your car: '88 Corvette: coupe, Z52, auto, 3.07, A/O intake, K&N, free mods, ported plenum, TPIS big mouth base, AS&M runners. Brake ducts, C5 calipers, Carbotech pads. Lowered, C5 silver thin spokes four 18x9.5".
But I see nothing about good sway bars or other suspension tweaks. The fact that you've "lowered" the car may very well mean you have now really screwed up the handling and probably changed the rake and angle of the car (which then makes your streamers go in funny directions). I hate it when that happens.
Stick with the big stuff my friend - seat time, suspension alignment and proper tuning, tires, brakes, seat time, tires, brakes, repeat as often as necessary.
07-24-2007, 04:59 PM
#5
Race Director
Thread Starter
I've had the car aligned, but cannot afford new sway bars this year. Next year maybe. I just finished the C5 caliper upgrade and have tires. So this stuff is free and helps cool the car for drag. What rake angle is good? I have read a few threads on that here but am still unsure how to measure it and if it really helps. I was looking at pictures of 200 MPH salt flat C4 race cars and they have zero rake. Why is that?
07-24-2007, 05:15 PM
#6
Team Owner
I've had the car aligned, but cannot afford new sway bars this year. Next year maybe. I just finished the C5 caliper upgrade and have tires. So this stuff is free and helps cool the car for drag. What rake angle is good? I have read a few threads on that here but am still unsure how to measure it and if it really helps. I was looking at pictures of 200 MPH salt flat C4 race cars and they have zero rake. Why is that?
1/2" is good rake measured from chassis at rear of front wheel and in front of rear wheel. I have a GS but forgot how the chassis is shaped. That is how I do it on the C5. Ball of yarn is cheap to play wind tunnel with.
Last edited by John Shiels; 07-24-2007 at 05:18 PM.
07-24-2007, 05:25 PM
#7
Melting Slicks
Go to this website to learn some basics about aerodynamics.
A poor man's way of wind tunnel testing is to put drops of oil on your car and then drive it at speeds you would see on the track. The oil will leave trails so you can see air flow around your car.
I learned this from one of the Chaparral race car mechanics. He said this is how they developed some of the aerodynamics on the cars back in the 60s. They didn't have wind tunnels like they have now so they would put drops on the car and go drive around their test track. We have plenty of dirt so it would stick to the oil streaks. You could see how the air flowed pretty easily.
I agree with wtknight1. Stick with the big stuff my friend - seat time, suspension alignment and proper tuning, tires, brakes, seat time, tires, brakes, repeat as often as necessary.
A poor man's way of wind tunnel testing is to put drops of oil on your car and then drive it at speeds you would see on the track. The oil will leave trails so you can see air flow around your car.
I learned this from one of the Chaparral race car mechanics. He said this is how they developed some of the aerodynamics on the cars back in the 60s. They didn't have wind tunnels like they have now so they would put drops on the car and go drive around their test track. We have plenty of dirt so it would stick to the oil streaks. You could see how the air flowed pretty easily.
I agree with wtknight1. Stick with the big stuff my friend - seat time, suspension alignment and proper tuning, tires, brakes, seat time, tires, brakes, repeat as often as necessary.
07-24-2007, 06:44 PM
#8
Race Director
Thread Starter
Ahh that makes sense with the salt racers. Ok, easy to follow the rake adjust. I put in adjustable rear sway bar end links and set them to match the stock link. When I go back to adjust them on the car, I will tweak the rake to. It's real close to 1/2" now. I can't find anything here 200 lbs to put in the drivers seat while I set the link.
07-24-2007, 07:33 PM
#9
Melting Slicks
Ahh that makes sense with the salt racers. Ok, easy to follow the rake adjust. I put in adjustable rear sway bar end links and set them to match the stock link. When I go back to adjust them on the car, I will tweak the rake to. It's real close to 1/2" now. I can't find anything here 200 lbs to put in the drivers seat while I set the link.
I've said several times on this forum that if you haven't taken your vette to Phoenix Performance (in PA), you really don't have any idea just how good your car can be!!!!!
07-24-2007, 08:47 PM
#10
Race Director
Thread Starter
Nice site above showing why rake makes downforce. My car won't be going to PA unless you are paying for it. 
07-24-2007, 10:02 PM
#12
Melting Slicks
Last edited by wtknght1; 07-25-2007 at 07:50 AM.
07-24-2007, 11:19 PM
#13
I've had the car aligned, but cannot afford new sway bars this year. Next year maybe. I just finished the C5 caliper upgrade and have tires. So this stuff is free and helps cool the car for drag. What rake angle is good? I have read a few threads on that here but am still unsure how to measure it and if it really helps. I was looking at pictures of 200 MPH salt flat C4 race cars and they have zero rake. Why is that?
Carl Johansson
Last edited by Carl Johansson; 07-24-2007 at 11:21 PM.
07-25-2007, 10:55 AM
#14
Race Director
Thread Starter
I don't know what pictures you are looking at - but the carter car - the moore brothers and any other C-4's I know of have significant rake - the rear end is quite a bit higher than the nose . It helps limit the amount of air going under the car - particularly when they are limited by rule to the stock airdam!
Carl Johansson
Carl Johansson
Lots of info:
The sleek silhouette of Ed and Linda Van Scoy’s 1985 Corvette stands in sharp contrast to Steve Rattie’s "Boss Brick." Aerodynamicists played at least as large a role in designing the final shape of Chevy’s fourth-generation Corvette as did its designers, with the end result being fantastic stability at high speed. This was of course a necessity given the fact that certain C4s, most notably those wearing the ZR1 package or Callaway’s twin-turbo option, were 170-plus mph cars right off the showroom floor.
The Van Scoys’ Corvette was a showpiece customized with Greenwood ground effects when they bought it in 1992. So as to conform to Grand Touring class rules, which permit only the addition of small, stabilizing roof rails and a hood scoop, the entire Greenwood package had to be removed.
Bonneville’s GT class rules dictate that certain components such as door panels remain in place, but otherwise allow considerable leeway in configuring the interior. The Van Scoys opted to replace their Corvette’s stock electronic instrumentation with Stewart Warner analog gauges. The factory radio remains however, and keeps Ed entertained while waiting in line for his turn to run. A Summit fiberglass racing seat replaced the driver-side factory seat and an oil tank took the place of the passenger seat. In keeping with established safety requirements, a full rollcage, five-point harness, and Flame Out Halon fire suppression system also occupy the interior.
Motive power comes from a small-block Chevy driving through a Corvette ZF six-speed and stock 4.11:1 geared differential. Mike LeFevers at Mitech Racing Engines in Placentia, California built the engine. All components were carefully selected to meet the rules, stay with the budget, and break the existing record. Configured for class C/GT, which allows a displacement from 306 to 372 cubes, it uses a 4.10-inch bore and 3.50-inch stroke to yield 370 cubic inches. Eagle rods, Arias pistons, Isky cam, Furia valves, COLA crank, Dart heads, a Holley Dominator, and MSD ignition combine for 625 hp @ 8200 rpm.
The custom, 15-inch steel wheels measure eight inches wide at the rear and four inches in front, and wear Goodyear tires. Talladega NASCAR slicks put the power to the salt at the rear and 4.5-inch wide Front Runners help keep it on the straight and narrow.
After blowing an engine in 1996’s event, Ed drove his Corvette to a new C/GT record in 1997 with a two-way average speed of 203.226 mph. In the years since ‘97 he upped his own mark several times, hitting 212.694 mph n 2000.
Like all Bonneville racers, the husband-and-wife Van Scoy team vows to return to the Salt once again. They will bring the same car but plan to swap their 372 stroker for a big block in order to run for the record in a different class.
07-25-2007, 01:53 PM
#15
I know Ed and his car pretty well. Ed was a big help in getting my 88 teched to run at Bonneville and El Mirage. You are right - the picture does not show much rake - but i can assure you - if you see it in person there is no doubt that it setup nose down *** high - probably 1 - 1.5 inches higher in the rear.
Here is a picture of the car with no rake:
Lots of info:
The sleek silhouette of Ed and Linda Van Scoy’s 1985 Corvette stands in sharp contrast to Steve Rattie’s "Boss Brick." Aerodynamicists played at least as large a role in designing the final shape of Chevy’s fourth-generation Corvette as did its designers, with the end result being fantastic stability at high speed. This was of course a necessity given the fact that certain C4s, most notably those wearing the ZR1 package or Callaway’s twin-turbo option, were 170-plus mph cars right off the showroom floor.
The Van Scoys’ Corvette was a showpiece customized with Greenwood ground effects when they bought it in 1992. So as to conform to Grand Touring class rules, which permit only the addition of small, stabilizing roof rails and a hood scoop, the entire Greenwood package had to be removed.
Bonneville’s GT class rules dictate that certain components such as door panels remain in place, but otherwise allow considerable leeway in configuring the interior. The Van Scoys opted to replace their Corvette’s stock electronic instrumentation with Stewart Warner analog gauges. The factory radio remains however, and keeps Ed entertained while waiting in line for his turn to run. A Summit fiberglass racing seat replaced the driver-side factory seat and an oil tank took the place of the passenger seat. In keeping with established safety requirements, a full rollcage, five-point harness, and Flame Out Halon fire suppression system also occupy the interior.
Motive power comes from a small-block Chevy driving through a Corvette ZF six-speed and stock 4.11:1 geared differential. Mike LeFevers at Mitech Racing Engines in Placentia, California built the engine. All components were carefully selected to meet the rules, stay with the budget, and break the existing record. Configured for class C/GT, which allows a displacement from 306 to 372 cubes, it uses a 4.10-inch bore and 3.50-inch stroke to yield 370 cubic inches. Eagle rods, Arias pistons, Isky cam, Furia valves, COLA crank, Dart heads, a Holley Dominator, and MSD ignition combine for 625 hp @ 8200 rpm.
The custom, 15-inch steel wheels measure eight inches wide at the rear and four inches in front, and wear Goodyear tires. Talladega NASCAR slicks put the power to the salt at the rear and 4.5-inch wide Front Runners help keep it on the straight and narrow.
After blowing an engine in 1996’s event, Ed drove his Corvette to a new C/GT record in 1997 with a two-way average speed of 203.226 mph. In the years since ‘97 he upped his own mark several times, hitting 212.694 mph n 2000.
Like all Bonneville racers, the husband-and-wife Van Scoy team vows to return to the Salt once again. They will bring the same car but plan to swap their 372 stroker for a big block in order to run for the record in a different class.
Lots of info:
The sleek silhouette of Ed and Linda Van Scoy’s 1985 Corvette stands in sharp contrast to Steve Rattie’s "Boss Brick." Aerodynamicists played at least as large a role in designing the final shape of Chevy’s fourth-generation Corvette as did its designers, with the end result being fantastic stability at high speed. This was of course a necessity given the fact that certain C4s, most notably those wearing the ZR1 package or Callaway’s twin-turbo option, were 170-plus mph cars right off the showroom floor.
The Van Scoys’ Corvette was a showpiece customized with Greenwood ground effects when they bought it in 1992. So as to conform to Grand Touring class rules, which permit only the addition of small, stabilizing roof rails and a hood scoop, the entire Greenwood package had to be removed.
Bonneville’s GT class rules dictate that certain components such as door panels remain in place, but otherwise allow considerable leeway in configuring the interior. The Van Scoys opted to replace their Corvette’s stock electronic instrumentation with Stewart Warner analog gauges. The factory radio remains however, and keeps Ed entertained while waiting in line for his turn to run. A Summit fiberglass racing seat replaced the driver-side factory seat and an oil tank took the place of the passenger seat. In keeping with established safety requirements, a full rollcage, five-point harness, and Flame Out Halon fire suppression system also occupy the interior.
Motive power comes from a small-block Chevy driving through a Corvette ZF six-speed and stock 4.11:1 geared differential. Mike LeFevers at Mitech Racing Engines in Placentia, California built the engine. All components were carefully selected to meet the rules, stay with the budget, and break the existing record. Configured for class C/GT, which allows a displacement from 306 to 372 cubes, it uses a 4.10-inch bore and 3.50-inch stroke to yield 370 cubic inches. Eagle rods, Arias pistons, Isky cam, Furia valves, COLA crank, Dart heads, a Holley Dominator, and MSD ignition combine for 625 hp @ 8200 rpm.
The custom, 15-inch steel wheels measure eight inches wide at the rear and four inches in front, and wear Goodyear tires. Talladega NASCAR slicks put the power to the salt at the rear and 4.5-inch wide Front Runners help keep it on the straight and narrow.
After blowing an engine in 1996’s event, Ed drove his Corvette to a new C/GT record in 1997 with a two-way average speed of 203.226 mph. In the years since ‘97 he upped his own mark several times, hitting 212.694 mph n 2000.
Like all Bonneville racers, the husband-and-wife Van Scoy team vows to return to the Salt once again. They will bring the same car but plan to swap their 372 stroker for a big block in order to run for the record in a different class.
07-25-2007, 04:13 PM
#16
Race Director
Thread Starter
I know Ed and his car pretty well. Ed was a big help in getting my 88 teched to run at Bonneville and El Mirage. You are right - the picture does not show much rake - but i can assure you - if you see it in person there is no doubt that it setup nose down *** high - probably 1 - 1.5 inches higher in the rear.
07-25-2007, 10:32 PM
#17
Team Owner
Member Since: Mar 2001
Location: Boston, Dallas, Detroit, SoCal, back to Boston MA
Posts: 30,596
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Have you looks at TCC's website?
http://www.tccracing.com/
Some ex Speed World Challenge cars there that make some serious downforce.
If you want to cut the hood, BTW by a separate skin and sell the hood it's worth a lot of $$$, you can do this
http://s64.photobucket.com/albums/h167/Tazio_Nuvolari/
http://www.tccracing.com/
Some ex Speed World Challenge cars there that make some serious downforce.
If you want to cut the hood, BTW by a separate skin and sell the hood it's worth a lot of $$$, you can do this
http://s64.photobucket.com/albums/h167/Tazio_Nuvolari/
07-25-2007, 11:17 PM
#18
Safety Car
The orange car was at Mid-Ohio two weeks ago with NASA...He was pitted just 50 yards away from me, but I never got the chance to go take a closer look. At the end of the day Saturday when I finally walked over the car was covered and the driver gone.
Unfortunately it looked like it blew a motor on Sunday, I saw smoke coming from the tailpipes for a few laps then didn't see the car anymore...
Unfortunately it looked like it blew a motor on Sunday, I saw smoke coming from the tailpipes for a few laps then didn't see the car anymore...
07-25-2007, 11:30 PM
#20
Safety Car
The best I saw over the two days was only a 1:40.xx...I assume it was a new owner not familiar with the car, since most of us in TT are running 1:37's or less.
It was unfortunate, since that car has been for sale as long as I've been a CF member. I was about to go buy it after my car caught on fire until I saw the motor go...
It was unfortunate, since that car has been for sale as long as I've been a CF member. I was about to go buy it after my car caught on fire until I saw the motor go...