Specifically 3rd gen Camaro [which is what I am building] [Ed once said we are all most interested in what applies to our cars and in general he is correct] especially the drag caused by the rear of body shape. What shape or spoiler can help?

Or, since it is 1/8 mile bracket racing, is it a non-issue?

To me, it seems it is important because the last 1/2 of the track is over 80 MPH. Also, if you are racing into a headwind the drag will be increased.

Any feedback?

Interesting question. Here is a link if it works on spoilers I found. Gotta love the internet!
CFD study on aerodynamic effects of a rear wing/spoiler on a passenger vehicle

Looking up on good old google a 1993-2002 Camaro is .34. I didn't see a chart with earlier years. To give a reference point a flipping astro can is .40. and a Honda Civic coupe is .29
There is a lot that goes into aerodynamics and I am no expert. In the actual drag force equation the velocity is squared which means it is 4x's at 200mph than it is at 100mph and same from 50 to 100. Doubling velocity will increase the drag force by four.

Drag Force =1/2 density x area x coefficient of drag.
I had to look it up. It's been a LONG time since fluid dynamics class.
It would be interesting to see if it made any ET difference but I'm guessing almost negligible. Try and see and let us know. Maybe it will feel a little more stable or if nothing else it looks cool.

quote:

Originally posted by BG7X77:
Interesting question. Here is a link if it works on spoilers I found. Gotta love the internet!
CFD study on aerodynamic effects of a rear wing/spoiler on a passenger vehicle

Looking up on good old google a 1993-2002 Camaro is .34. I didn't see a chart with earlier years. To give a reference point a flipping astro can is .40. and a Honda Civic coupe is .29
There is a lot that goes into aerodynamics and I am no expert. In the actual drag force equation the velocity is squared which means it is 4x's at 200mph than it is at 100mph and same from 50 to 100. Doubling velocity will increase the drag force by four.

Drag Force =1/2 density x area x coefficient of drag.
I had to look it up. It's been a LONG time since fluid dynamics class.
It would be interesting to see if it made any ET difference but I'm guessing almost negligible. Try and see and let us know. Maybe it will feel a little more stable or if nothing else it looks cool.

You are incorrect of your formula...

Basic wind pressure = .00256 x V^2 (lbs/ft^2)

Basic Wind Drag Force = wind pressure x area x CD


In the big picture I doubt you would ever see any difference messing with rear spoilers on a car running 1/8 mile for bracket racing. Spend you time looking elsewhere.

The formula I posted is the basic Drag Force equation. Neither yours or mine are WRONG. I would agree yours is much easier to use for this application. I appreciate the discussion.

Dragster slows down half as much as a typical Super Pro doorslammer, when a head wind kicks up.

I'd imagine aerodynamics put in this context, explains why diminishing high pressure area's on the car are beneficial to the cause, possibly.

For a factory condition Nova, I think my car is pretty decent in the front, grill is closed off. I think the hood probably diminish's the high pressure area's of the windshield alright.

I think it's a subjective matter, a little common sense may go furthest.

This message has been edited. Last edited by: Mike Rietow,

quote:

Originally posted by BG7X77:
The formula I posted is the basic Drag Force equation. Neither yours or mine are WRONG. I would agree yours is much easier to use for this application. I appreciate the discussion.

Not trying to start any here, no yours is wrong or incomplete.

quote:

Originally posted by Mike Rietow:
Dragster slows down half as much as a typical Super Pro doorslammer, when a head wind kicks up.

I'd imagine aerodynamics put in this context, explains why diminishing high pressure area's on the car are beneficial to the cause, possibly.

For a factory condition Nova, I think my car is pretty decent in the front, grill is closed off. I think the hood probably diminish's the high pressure area's of the windshield alright.

I think it's a subjective matter, a little common sense may go furthest.

Dragsters are about twice as dirty vs door cars with regards to CD's. The projected area of dragsters is not much smaller than door cars.

Dragsters that are less effected by head winds is do to HP/Weight ratio which is much higher than typical door cars. However I'd bet some slippery door cars with decent power are less effected than dragsters.

I stand corrected. I omitted the velocity squared that I was referring to in the post. Duh!

Drag Force=1/2 density x area x coefficient of drag x velocity squared


Thank you!

quote:

Originally posted by TOP38:

quote:

Originally posted by Mike Rietow:
Dragster slows down half as much as a typical Super Pro doorslammer, when a head wind kicks up.

I'd imagine aerodynamics put in this context, explains why diminishing high pressure area's on the car are beneficial to the cause, possibly.

For a factory condition Nova, I think my car is pretty decent in the front, grill is closed off. I think the hood probably diminish's the high pressure area's of the windshield alright.

I think it's a subjective matter, a little common sense may go furthest.

Dragsters are about twice as dirty vs door cars with regards to CD's. The projected area of dragsters is not much smaller than door cars.

Dragsters that are less effected by head winds is do to HP/Weight ratio which is much higher than typical door cars. However I'd bet some slippery door cars with decent power are less effected than dragsters.

I'm talking dragster in comparison typical brick shaped Super Pro doorslammer rocked back, front end up at the stripe.

You're talking dragster in comparison to tear drop shaped pro stocker sitting on the starting line.

Big difference.

Take a piece of plywood, hold it level to the ground at your belt, then tilt it up slightly into the wind..

High pressure underneath the plywood is the drag on a typical doorslammer rocked back front end up.

Using common sense takes us furthest, on this subjective topic.

This message has been edited. Last edited by: Mike Rietow,

OP,

The more it looks like a tear drop, the better.

Tear drop is premium.

If you can get away with running the rebound tight on the front dampers and the compression loose, it'll pull the front down if you close in the front, it'll be high pressure on the nose / windshield, instead of the entire underside of the car, nose / windshield.

This message has been edited. Last edited by: Mike Rietow,

Headwinds don't affect my Cobalt much at all.

I guess we are way off in the weeds now. You are correct on the teardrop shape is theoretically optimal. Aerodynamics is a very intense discipline and chaotic (small changes creating large differences in outcome), however it is not subjective. It is simply a very difficult thing to quantify hence Computational Fluid Dynamic programs were developed to attempt to predict actual happenings. Even these are limited by boundary conditions, and assumptions that need to be made. There is always way more to it than simple.....down force on the car so it doesn't fly away and you can actually drive it, etc. ect. It is one of those subjects that is intriguing, however I am not even close to knowing the nuances and intricacies of.

But back to the OP question. Whatever looks cooler. Go with that. On that style Camaro I say spoiler yes or a nicely done small wing but it ain't my ride.

quote:

Originally posted by BG7X77:
I guess we are way off in the weeds now. You are correct on the teardrop shape is theoretically optimal. Aerodynamics is a very intense discipline and chaotic (small changes creating large differences in outcome), however it is not subjective. It is simply a very difficult thing to quantify hence Computational Fluid Dynamic programs were developed to attempt to predict actual happenings. Even these are limited by boundary conditions, and assumptions that need to be made. There is always way more to it than simple.....down force on the car so it doesn't fly away and you can actually drive it, etc. ect. It is one of those subjects that is intriguing, however I am not even close to knowing the nuances and intricacies of.

But back to the OP question. Whatever looks cooler. Go with that. On that style Camaro I say spoiler yes or a nicely done small wing but it ain't my ride.

I have no way of providing any factual evidence of anything I'm injecting into this conversation. I'm relying on your common sense to comprehend my rudimentary examples, i've used to formulate an approach on my car.

I understand there are tools which make the topic objective, but they'll never see these pages.

Just so you understand what I mean by subjective. I think the examples i've added are fairly useful but I have no factual evidence to include.

This message has been edited. Last edited by: Mike Rietow,

Fair enough. If you get a chance read that paper I attached. Some of it is a little obscure but there are some interesting facts on the "wake" of the vehicle and down force.

quote:

Originally posted by Mike Rietow:

quote:

Originally posted by TOP38:

quote:

Originally posted by Mike Rietow:
Dragster slows down half as much as a typical Super Pro doorslammer, when a head wind kicks up.

I'd imagine aerodynamics put in this context, explains why diminishing high pressure area's on the car are beneficial to the cause, possibly.

For a factory condition Nova, I think my car is pretty decent in the front, grill is closed off. I think the hood probably diminish's the high pressure area's of the windshield alright.

I think it's a subjective matter, a little common sense may go furthest.

Dragsters are about twice as dirty vs door cars with regards to CD's. The projected area of dragsters is not much smaller than door cars.

Dragsters that are less effected by head winds is do to HP/Weight ratio which is much higher than typical door cars. However I'd bet some slippery door cars with decent power are less effected than dragsters.

I'm talking dragster in comparison typical brick shaped Super Pro doorslammer rocked back, front end up at the stripe.

You're talking dragster in comparison to tear drop shaped pro stocker sitting on the starting line.

Big difference.

Take a piece of plywood, hold it level to the ground at your belt, then tilt it up slightly into the wind..

High pressure underneath the plywood is the drag on a typical doorslammer rocked back front end up.

Using common sense takes us furthest, on this subjective topic.

NO! No super slick PS considered cars in my previous post.

I think rerun reitow just likes postin pics of his triple chrome front bumper

quote:

Originally posted by BG7X77:
Fair enough. If you get a chance read that paper I attached. Some of it is a little obscure but there are some interesting facts on the "wake" of the vehicle and down force.

Thanks, I'll definitely do that. We've got a new build, 275 radial car we have yet to run, that will be in the 140 mph range 1/8 mile with a NOS cheater plate on a sbc 4150 intake manifold.

This message has been edited. Last edited by: Mike Rietow,

There are basic forces involved in a vehicle traveling a straight line on level ground;

• Inertial Force (F= ma
  
• Traction Force (tire friction)
  
• Road Load Force (based on driveline efficiency)
  
• Aero drag
  

Multiply every one of them times velocity and you get the power it takes for each of the forces.
Aero would make sense to address since it now has a velocity cubed term. Blocking off the radiator is one of the bigger "freebies". Changing Cd is really hard - the mention of the wake zone is noteworthy as the pressure gradient at the back of the car is huge. That's one of the reasons of the decklid extension on PS and PM cars - extending the length where high pressure mixes with low pressure slightly reduces drag.

Vehicle mass is the quantity that everyone is familiar with and is the easiest to make happen. thee is one component of mass that is lumped in and it's an equivalent mass that represents the rotating inertia of the transmission, crankshaft, driveshaft, and rear end.

To get an idea of if there is a big payback on any of them, there are many drag race simulators like Quarter Pro that actually have numbers you enter for each of the forces listed above. Match the program's output to your time slip and then change CD, or frontal area, or rotating inertia, and car weight.

Several years ago I fabricated a new rear wing for my Davis '27 roadster. I reduced the height of the side wings for greater visibility and lowered the attack angle hoping that it would increase the car speed. That worked, the car picked up speed but the trade off was that it lost some stability in high gear. To counteract that I added an adjustable Gurney Flap to the rear spoiler to see if it would add stability. The results were interesting. It actually didn't add as much drag as I thought it would so it retained the same speed but it certainly did make the car more stable.

The range of adjustment runs from zero (dead flat) to 1/2 inch high. At a .375 inch the car felt a lot more stable in high gear and it didn't adversely effect the speed. The overall result of this process was that the car is less effected by head or tail winds and more stable.

I wonder if anyone else has played with the Gurney Flat design? If so, I would like to hear about your experience.

Bob

Years ago I raced a 94 Lumina super gas/comp car, even when the wind was blowing straight down the track at Sears Point it had very little effect, while a tail wind would pick me up substantially.