cut outs in the rear bumper
The whole thing doesn't seem to be very well thought out.
08-27-2010, 12:08 PM
#19
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Location: Minneapolis, Minnesota
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I'm the previous owner, and no, I didn't do it because of looks. Once I stopped licensing it, I cut out the license plate box for air. Not long after, I decided to go for more. How much power do you think it would require to drag that bumper/parachute over 120 mph (my top speed at ECR)? I don't know, but probably more than a little bit. 
I like Mike's diffuser much better, and would have gone that route had I kept the car. I don't like the wing either, and the stupid thing weighs 20 lbs, but there is good evidence to suggest that it works. Then there are the ground effects. I thought long and hard about putting these on, but once you have drank the aero Kool-aid, there's no turning back. Mike and I hit 144 mph at Texas Motor Speedway. Who knows, maybe my ground effects and his diffuser and front splitter kept us from losing grip and kissing the wall! We were probably not that close to the limit, but I wouldn't want to test the limit and my reflexes at that speed. The wheels are CCW 3-piece with forged centers. The car is sold now, and time for someone else to develop it.
I like Mike's diffuser much better, and would have gone that route had I kept the car. I don't like the wing either, and the stupid thing weighs 20 lbs, but there is good evidence to suggest that it works. Then there are the ground effects. I thought long and hard about putting these on, but once you have drank the aero Kool-aid, there's no turning back. Mike and I hit 144 mph at Texas Motor Speedway. Who knows, maybe my ground effects and his diffuser and front splitter kept us from losing grip and kissing the wall! We were probably not that close to the limit, but I wouldn't want to test the limit and my reflexes at that speed. The wheels are CCW 3-piece with forged centers. The car is sold now, and time for someone else to develop it.Last edited by Mikes 1994 z28; 08-27-2010 at 12:12 PM.
08-30-2010, 10:50 AM
#21
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Location: Friendswood, TX, USA
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Saying you did 144 here and 120 there, doesn't tell us much. With the cd/A of a stock Camaro you only need about 200hp to do 150mph.
Anyway, there is one "subjective" measure that's an indicator of whether it's a good idea or not. Do you see it on any modern professional race cars?
08-30-2010, 03:49 PM
#22
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08-30-2010, 11:16 PM
#23
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Not sure what you mean by "do you see IT on any modern race cars", but you don't need windtunnel data to take theory that has been proven for many years and apply it using some sound reasoning. A very good book on this subject is Competition Car Downforce by Simon McBeath. It's kind of the bible on this subject. I don't like to use NASCAR as a model for technology, but I think they have enough wind tunnel data to tell them that the spoiler and the ground effects/side skirts are working for them. As for the slots, modern race cars have diffusers to remove the air, so the air can't get into the bumper/parachute. But in those places where the diffuser principle cannot be used, race cars often have slots in the bumper. Do a Google image search for Porsche GT1. Just because these cars have a decent Cd, doesn't mean that it can't be made better. There is a lot of dirty air underneath these cars. Sure, they may do 150 mph with 200 hp, but road racing is about accelerations between turns, not just getting up to a certain speed. It is also about pushing as close to the limit in turns as possible, and that comes from traction, which is grip X normal force, or downforce. Though it may not be major, the faster the air moves under the car, the greater the reduction in Bernoulli effect from the top side of the car, another principle that I don't need a wind tunnel to prove. It all translates to downforce, and I'll take every pound I can get.
08-31-2010, 08:25 AM
#24
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I love that car from the tip of the nose to the end of the spoiler. From the blacked out headlights to the spoiler and the bumper cutouts. Not only it's functional, it looks mean from every angle. You show up with this car anywhere and you will turn heads. It looks like nothing other than a fire breathing race car. With the exception of that "for sale" decal, of course.
This car is evidence 4th gens can handle, and something all of us Camaro owners can be proud of. It's proof Camaros are more than "good ol' muscle car" wanna-bes, and can stand on their own feet against the best of the best not only on the straights, but in the corners too.
Now let's see you trash talkers make something nearly as good in the corners. Till then, shut the hell up.
This car is evidence 4th gens can handle, and something all of us Camaro owners can be proud of. It's proof Camaros are more than "good ol' muscle car" wanna-bes, and can stand on their own feet against the best of the best not only on the straights, but in the corners too.
Now let's see you trash talkers make something nearly as good in the corners. Till then, shut the hell up.
08-31-2010, 12:00 PM
#25
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A very good book on this subject is Competition Car Downforce by Simon McBeath. It's kind of the bible on this subject. I don't like to use NASCAR as a model for technology, but I think they have enough wind tunnel data to tell them that the spoiler and the ground effects/side skirts are working for them.
As for the slots, modern race cars have diffusers to remove the air, so the air can't get into the bumper/parachute.
But in those places where the diffuser principle cannot be used, race cars often have slots in the bumper. Do a Google image search for Porsche GT1.
One of the biggest problems of the 993 GT2 was the location of the engine that did not permit the use of venturis. These were essential to achieve sufficient downforce on the flat bottomed car so the designers decided to rotate the six cylinder engine around, making the GT1 the first mid-engined 911.
These are NOT holes in the bumper to let air out. The engine was moved to allow, "venturis" i.e. a diffuser. There are some small vents in the back but they're outlets for the oil coolers. The C6R has the license plate area the same way. It's for the oil coolers, not to let air out of the car or out from under the car.
Just because these cars have a decent Cd, doesn't mean that it can't be made better. There is a lot of dirty air underneath these cars. Sure, they may do 150 mph with 200 hp, but road racing is about accelerations between turns, not just getting up to a certain speed. It is also about pushing as close to the limit in turns as possible, and that comes from traction, which is grip X normal force, or downforce. Though it may not be major, the faster the air moves under the car, the greater the reduction in Bernoulli effect from the top side of the car, another principle that I don't need a wind tunnel to prove. It all translates to downforce, and I'll take every pound I can get.
08-31-2010, 01:54 PM
#26
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Location: Dallas, Texas
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4th gen Camaros' rear bumpers act like a parachute to some extent, which is why Callaway redid the rear of the Callaway C8. His holes likely help get rid of the air, but it almost makes you wonder if it'd be better without a bumper at all.
08-31-2010, 03:55 PM
#27
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Join Date: Nov 2006
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I love the contrast between post #24 and #25!
It's also important to note that the parachute effect appeared more significant after cutting out most of the sheetmetal from the rear axle back, including the inner fenders to reduce weight. It was just the bumper hanging out there with nothing behind it connected only to the body, and a couple straps on the bottom to keep it from flopping around.I think removing the rear bumper would be even better, but man would that look terrible! If I were to go that far, I would have just removed the tail lights, the filler panel with Camaro lettering, etc. Make it look like a late model stock car completely open in the back. Hey, maybe that's the "modern" race car example for you!
OK, so "remove" the air was the wrong word. Clean up the air would have been better, but the cleaner and less turbulent the air, the quicker it is removed. I think the reason that this is not seen on modern race cars is because everything has diffusers, so the air cannot get up there anyway. I didn't build a diffuser for various reasons, time being the biggest. But if you look around, I think you will find examples of this practice. I can't be sure, but I think the blacked out areas on the Ford RS200 Rally car are screens for removing air.
If I ran with an umbrella behind me with a force gauge between me and the umbrella, then I cut holes in the umbrella and measured smaller readings, would that be proving it practically, or theoretically? If I still had the car I could tie strings to the cut-outs to prove that the pressure is not negative in that area, as that is the only way I can see that they would slow me down. I think you are trying pretty hard to play devil's advocate. Does anyone else reading this thread really think that cutting holes in the parachute/bumper SLOWED ME DOWN?
I think you're bothered that I cut up something you consider sacred in order to go faster.
Regardless of the bumper, what I have proven with GPS data is that I can make a Camaro pull 2g, and make some VERY expensive cars at the track look pretty silly with a Camaro with a $10K for sale sign on the spoiler, which was intentional.
It's also important to note that the parachute effect appeared more significant after cutting out most of the sheetmetal from the rear axle back, including the inner fenders to reduce weight. It was just the bumper hanging out there with nothing behind it connected only to the body, and a couple straps on the bottom to keep it from flopping around.I think removing the rear bumper would be even better, but man would that look terrible! If I were to go that far, I would have just removed the tail lights, the filler panel with Camaro lettering, etc. Make it look like a late model stock car completely open in the back. Hey, maybe that's the "modern" race car example for you!
OK, so "remove" the air was the wrong word. Clean up the air would have been better, but the cleaner and less turbulent the air, the quicker it is removed. I think the reason that this is not seen on modern race cars is because everything has diffusers, so the air cannot get up there anyway. I didn't build a diffuser for various reasons, time being the biggest. But if you look around, I think you will find examples of this practice. I can't be sure, but I think the blacked out areas on the Ford RS200 Rally car are screens for removing air.
If I ran with an umbrella behind me with a force gauge between me and the umbrella, then I cut holes in the umbrella and measured smaller readings, would that be proving it practically, or theoretically? If I still had the car I could tie strings to the cut-outs to prove that the pressure is not negative in that area, as that is the only way I can see that they would slow me down. I think you are trying pretty hard to play devil's advocate. Does anyone else reading this thread really think that cutting holes in the parachute/bumper SLOWED ME DOWN?
I think you're bothered that I cut up something you consider sacred in order to go faster.
Regardless of the bumper, what I have proven with GPS data is that I can make a Camaro pull 2g, and make some VERY expensive cars at the track look pretty silly with a Camaro with a $10K for sale sign on the spoiler, which was intentional.
Last edited by full_tilt; 08-31-2010 at 04:07 PM.
08-31-2010, 04:01 PM
#28
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Location: Friendswood, TX, USA
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I believe these are to releave the high pressure created by the rear tire rotation, from the fender well not from the bumper. It's a very simple thing to build a pan that incloses this area, that way the air doesn't get in there in the first place!
08-31-2010, 10:29 PM
#29
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Join Date: Nov 2006
Posts: 16
I'll agree that a pan would have been better, but it would not have been simple and I spent a lot of time thinking about it. My fuel cell hung down just behind the differential cover and panhard bar that moves up and down obviously. I didn't want to start the pan just anywhere, as it would once again catch air into the rear cavity. However, a pan that continued from the body in front of the axle and continued underneath the axle would have been extremely difficult, especially with the welded lower control arm brackets that extend much lower than the stock control arm brackets/shock mounts. Seemed to me like it would have been anything but simple.
