[LiL Jack]

Originally Posted by Stan Weiss

Lil Jack,
Thank you for that information.

Stan

No problem Stan, just trying to move the Pontiac community forward.

In all seriousness what does you come up with on Jeff's junk?

[Stan Weiss]

Originally Posted by LiL Jack

No problem Stan, just trying to move the Pontiac community forward.

In all seriousness what does you come up with on Jeff's junk?

Lil Jack,
There are many variables like traction and Density Altitude that have an impact on what Dyno HP is need to run a et / mph. The et from my simulation comes out very close but I am about 1.5 MPH lower. But I have no solid numbers to work with (CD / frontal area) for aerodynamic drag.

Stan

[LiL Jack]

Originally Posted by Stan Weiss

Lil Jack,
There are many variables like traction and Density Altitude that have an impact on what Dyno HP is need to run a et / mph. The et from my simulation comes out very close but I am about 1.5 MPH lower. But I have no solid numbers to work with (CD / frontal area) for aerodynamic drag.

Stan

What is your best guess?

[Tom Vaught]

Originally Posted by Stan Weiss

Lil Jack,
There are many variables like traction and Density Altitude that have an impact on what Dyno HP is need to run a et / mph. The et from my simulation comes out very close but I am about 1.5 MPH lower. But I have no solid numbers to work with (CD / frontal area) for aerodynamic drag.

Stan

You could get Jeff and Jack to give you an approximation on the Frontal Area,
Stan using Equation #2:

AF= (H-GC) W*0.93
where: H is the vehicle height
GC is the ground clearance
W is the width.

Better than nothing if they could "rough measure" the car.

Then do a "sweep" on Cd from .46 to .55


Tom V.

[Stan Weiss]

Originally Posted by Tom Vaught

You could get Jeff and Jack to give you an approximation on the Frontal Area,
Stan using Equation #2:

AF= (H-GC) W*0.93
where: H is the vehicle height
GC is the ground clearance
W is the width.

Better than nothing if they could "rough measure" the car.

Then do a "sweep" on Cd from .46 to .55


Tom V.

Tom,
While a production car is fairly level, a race race has more of a wedge shape to it. With a much greater ground clearance in the back than the front. Where do they measure ground clearance and how well will that work with this formula?

Stan

PS - This thread that I have been spending sometime posting in and maybe of interest to some of you.
dynamic compression for the street.
http://www.yellowbullet.com/forum/sh...1#post16089354

[Tom Vaught]

Originally Posted by Stan Weiss

Tom,
While a production car is fairly level, a race race has more of a wedge shape to it. With a much greater ground clearance in the back than the front. Where do they measure ground clearance and how well will that work with this formula?

Stan

PS - This thread that I have been spending sometime posting in and maybe of interest to some of you.
dynamic compression for the street.
http://www.yellowbullet.com/forum/sh...1#post16089354

Good question.

1) You would like to keep the air out of the underneath of the car. Not having the air bang around on all of the suspension components and drive line stuff. The only way to do that is to minimize the air that gets under the car.

2) Air also can get under the car from the wheel openings. Most good front air dams keep the air from entering the wheel houses from the side.

3) So now if you limit the amount of air coming thru the grill to the minimum required for cooling (more road race vs drag race) you can reduce the air flow under the car quite a bit.

4) Air, by the time it gets to the rear edge of the door is starting to get dirty so having small deflectors at the front of the rear wheel openings might help on a street car or car with a very shallow tire/wheel depth. A Drag car has the tire sunk into the body pretty well so minimal rear tire impact contacting the air from the sides really.

5) Transitions from things like the windshield or doors to the body can make a difference in how smooth the car is going thru the air.

So after saying all of that, if the rear of the car has more of a rake vs the front then, yes, so dirty air can eventually get under the car but the big deal is not allowing the air to get under the front of the car.

Where does the cooling air from the radiator go, typically under the car, unless you have a Trans Am type side extractor set-up (which actually worked pretty well). Less air getting into the engine compartment, less air banging around on the firewall trying to act like a parachute that slows the car down.

So the front of the vehicle is where the measurements need to be taken. Measure at the lowest point of the spoiler to the ground (if it has one). You can document the rake angle, (which we do) but the effect is minimal in normal testing. I built screw jackers to raise and the rear of the vehicle quickly, when it went into the wind tunnel. 4" difference in high rake vs low rake showed an effect but a small one vs the front height change of the vehicle.

So a) measure from the spoiler to the ground and that area you subtract from the area calculated in the measurement from the ground to the top of the windshield. Also add the tire frontal area (footprint of the tire when looking at the tire at the spoiler height). Then do the math in the formula.


Hope that helps with your question.

Tom V.

[Stan Weiss]

Originally Posted by Tom Vaught

Good question.

1) You would like to keep the air out of the underneath of the car. Not having the air bang around on all of the suspension components and drive line stuff. The only way to do that is to minimize the air that gets under the car.

2) Air also can get under the car from the wheel openings. Most good front air dams keep the air from entering the wheel houses from the side.

3) So now if you limit the amount of air coming thru the grill to the minimum required for cooling (more road race vs drag race) you can reduce the air flow under the car quite a bit.

4) Air, by the time it gets to the rear edge of the door is starting to get dirty so having small deflectors at the front of the rear wheel openings might help on a street car or car with a very shallow tire/wheel depth. A Drag car has the tire sunk into the body pretty well so minimal rear tire impact contacting the air from the sides really.

5) Transitions from things like the windshield or doors to the body can make a difference in how smooth the car is going thru the air.

So after saying all of that, if the rear of the car has more of a rake vs the front then, yes, so dirty air can eventually get under the car but the big deal is not allowing the air to get under the front of the car.

Where does the cooling air from the radiator go, typically under the car, unless you have a Trans Am type side extractor set-up (which actually worked pretty well). Less air getting into the engine compartment, less air banging around on the firewall trying to act like a parachute that slows the car down.

So the front of the vehicle is where the measurements need to be taken. Measure at the lowest point of the spoiler to the ground (if it has one). You can document the rake angle, (which we do) but the effect is minimal in normal testing. I built screw jackers to raise and the rear of the vehicle quickly, when it went into the wind tunnel. 4" difference in high rake vs low rake showed an effect but a small one vs the front height change of the vehicle.

So a) measure from the spoiler to the ground and that area you subtract from the area calculated in the measurement from the ground to the top of the windshield. Also add the tire frontal area (footprint of the tire when looking at the tire at the spoiler height). Then do the math in the formula.


Hope that helps with your question.

Tom V.

Tom,
Thanks.
As an aside. I see people try to save weight by not running inter front fender wells. How much of a negative effect would this have?

Stan

[mike leech]

Originally Posted by Stan Weiss

Tom,
Thanks.
As an aside. I see people try to save weight by not running inter front fender wells. How much of a negative effect would this have?

Stan

I would have addressed you as well in my last post had i noticed this post first.

[mike leech]

Originally Posted by Tom Vaught

Good question.

1) You would like to keep the air out of the underneath of the car. Not having the air bang around on all of the suspension components and drive line stuff. The only way to do that is to minimize the air that gets under the car.

2) Air also can get under the car from the wheel openings. Most good front air dams keep the air from entering the wheel houses from the side.

3) So now if you limit the amount of air coming thru the grill to the minimum required for cooling (more road race vs drag race) you can reduce the air flow under the car quite a bit.

4) Air, by the time it gets to the rear edge of the door is starting to get dirty so having small deflectors at the front of the rear wheel openings might help on a street car or car with a very shallow tire/wheel depth. A Drag car has the tire sunk into the body pretty well so minimal rear tire impact contacting the air from the sides really.

5) Transitions from things like the windshield or doors to the body can make a difference in how smooth the car is going thru the air.

So after saying all of that, if the rear of the car has more of a rake vs the front then, yes, so dirty air can eventually get under the car but the big deal is not allowing the air to get under the front of the car.

Where does the cooling air from the radiator go, typically under the car, unless you have a Trans Am type side extractor set-up (which actually worked pretty well). Less air getting into the engine compartment, less air banging around on the firewall trying to act like a parachute that slows the car down.

So the front of the vehicle is where the measurements need to be taken. Measure at the lowest point of the spoiler to the ground (if it has one). You can document the rake angle, (which we do) but the effect is minimal in normal testing. I built screw jackers to raise and the rear of the vehicle quickly, when it went into the wind tunnel. 4" difference in high rake vs low rake showed an effect but a small one vs the front height change of the vehicle.

So a) measure from the spoiler to the ground and that area you subtract from the area calculated in the measurement from the ground to the top of the windshield. Also add the tire frontal area (footprint of the tire when looking at the tire at the spoiler height). Then do the math in the formula.


Hope that helps with your question.

Tom V.

I know for a fact that removing the factory wheel wells from a early camaro/firebird will cause a low 12 car to lose 2 mph. et was about the same, a touch slower. air hitting the fire wall is a bad deal and care should be taken to limit introduction as well as relieving any built up pressure under the hood. these would have an effect on how the car moves through the air as well

[Tom Vaught]

Originally Posted by Stan Weiss

Tom, Thanks.
As an aside. I see people try to save weight by not running inter front fender wells. How much of a negative effect would this have?

Stan

[/QUOTE]

Originally Posted by mike leech

I know for a fact that removing the factory wheel wells from a early camaro/firebird will cause a low 12 car to lose 2 mph. et was about the same, a touch slower. air hitting the fire wall is a bad deal and care should be taken to limit introduction as well as relieving any built up pressure under the hood. these would have an effect on how the car moves through the air as well

Real world info (from Mike) that mirrors the testing we did in the wind tunnel. Only issue is that you need SOME leakage airflow to carry away the heat from the engine compartment on a production vehicle or the components will get too hot to survive for 150.000 miles. Removing the inner fender wells completely normally will allow more air to be in the compartment with the air now trying to figure out how to get out vs giving it a controlled escape path.
Belly Pans, sealed fender wells, etc can cause the underhood temps to skyrocket.

Tom V.