Here's a little info on2287 at Bonneville. Sorry if the links don't work well (I need to update my site)

http://www3.telus.net/carstairs-crui.../daytona2a.htm

Turbo II
Thanks for the link--pretty awesome IMO--given the technology and conditions of the day

Long Reply (Part 1 of 2)
 

> The GT-40 was not designed in a wind tunnel.

Actually it was but it was a learning experience. 76 individual wind
tunnel tests were carried out in the Maryland University wind tunnel on
a 3/8 scale model to arrive at the original GT40 MKI body shape. Based
upon those tests, a full-size model was built and tested at Ford's own
wind tunnel in Dearborn. Ford used the Lola GT as a baseline, comparing
it to various revisions of the baseline GT40 shape. The forum software
may screw up the formatting but some results are presented below:

Vehicle Yaw Speed Lift Lift Lift Drag
(MPH) Front Rear Total (lb)
(lb) (lb) (lb)

-----------------------------------------------------------------
Lola GT 0 200 528 168 696 503
15 200 768 384 1152
-----------------------------------------------------------------
GT40 with 0 200 540 108 648 519
High Nose 15 200 844 362 1206 614
-----------------------------------------------------------------
GT40 with 0 200 445 199 644 507
Low Nose 15 200 704 422 1126 596
-----------------------------------------------------------------
Front Spoiler 0 200 326 266 592 513
#1
-----------------------------------------------------------------
Front Spoiler - 200 --- --- --- 531
#2
-----------------------------------------------------------------
Front Spoiler 0 200 236 272 508 488
#3 15 200 309 343 652 591
-----------------------------------------------------------------

Front spoiler #1 was 2.67 tall and was added below nose, behind the
air intake. Front spoiler #2 was in the same location but twice as
tall. It reduced lift but was deemed to not have enough ground
clearance. Front spoiler #3 was 3 1/2" tall and faired in. Recessed
headlights were chosen as raised headlights resulted in "marked increases
in lift and drag".

Many of the tests were directed towards trying to find the lowest drag
way to provide air flow for the cooling system, the induction, engine
compartment ventilation, interior ventilation, and brake and shock
absorber cooling air. The designers originally wanted to use twin side
radiators mounted in the engine compartment but tests on the full scale
wind tunnel model indicated 8000 CFM would be required which was deemed
not possible with the side intake duct layout. A conventional front
mounted radiator with intake and outlet beneath the nose was a little
better. The final solution was to take air in at the high pressure
region below the nose, let it flow past an angled radiator and exhaust
out the low pressure region at the top of the nose bodywork. Anti-dive
and squat were designed into the suspension to keep the cars more level
so as to not upset the aerodynamics.

Even with all the wind tunnel work, Ford was learning as they went and
the GT40's airflow management proved insufficient once the cars got out
in the field. The wind tunnel models were not fitted with the internal
ducting so it was only later discovered that 76 horsepower were being
consumed up just trying to ram air through the car at high speed. The
cars were modified in the field to fix one problem like cooling only
to change another, like the aerodynamic balance resulting in yet another
problem. Ken Miles spoke of the problem:

"The aerodynamic problems we've had with the car were essentially ones of
air flow within the car being affected by external details. For example
we were getting very little air flow to the brakes, although they had huge
ducts ostensibly directing vast quantities of air at them. In fact, the
brakes were overheating badly. The engine was getting too hot. The
engine compartment itself was getting too hot. The cooling water was
getting too hot. The engine and gearbox oil was gettting too hot. All
this in spite of a large number of aperatures which should have supplied
them with more than enough air. We discovered that what was happening was
that due to design changes that had been made over a period of time,
probably without reference to the original specifications practically all
of the ductwork was at a "stall " condition" i.e. no air was moving in the
ducts".

Ford's aeronspace division Aeronutronics was brought in to instrument a
GT40 with pressure and temerature sensors on various parts of the body
(externally and inside the ducts). From this data, the Shelby team was
able to modify the cars properly. Even when the MKII's appeared, Ford
still had some aerodynamic lessons to learn. Phil Hill wrote "The second
year at LeMans we were in deep trouble when we first arrived, thanks
to a diabolical instability that had been supposedly eliminated in
stateside testing. The MKII's were simply terrifying down the Mulsanne
Straight. We ended up tacking on little eyebrow spoilers as well as an
additional little spoiler across the back to solve the problem. I also
remember early Ferraris with so much front end lift that the steering
became progressively lighter as speed climbed until finally the rebound
stops were a factor... we could have called it up-force."

> Don't know what the drag is for a Coupe, but according to the Nov
> 2003 Car and Driver article about the "new" GT-40, the "old" GT-40
> had a c/d of "about .43". Not as aerodynamic as it appears.

A few things to remember. A low Cd number is only part of the battle.
It gets multipled by the frontal area, so its the product of the two
that determines the overall drag. In addition to minimizing drag, a
primary goal is to reduce lift (or better yet generate downforce) and
have a balance of lift front and rear for stability. Plus you need to
make provisions for cooling flow for brakes, engine, driver, etc. Also
"Aerodynamic" does not necessarily mean low drag. Formula 1 race cars
are very aerodynamic but have horrible drag. That's because they gladly
trade downforce and balance for drag. Note that wings generally do not
decrease drag. Quite the contrary, they typically increase drag.

The earliest of the original GT40's had a Cd of around 0.3, very good
for the time. However, once in the field a number of problems were
encountered that required changes to the original shape and hurt the
drag.

An old GT40 sales brochure mentioned that in 1964, Phil Hill drove a GT40
at LeMans that hit 207 MPH on the Mulsanne straight. That speed was
supposedly achieved with the 4.2 liter Indy engine which made 375 horsepower
at 7300 RPM. A first order approximation estimate of a car's top speed can
be computed using the following formula:

/------------
15 / 1100 P
Vmax = ---- \ 3 / -------------
22 \ / Cd S rho
\/

where

P..........Power in rear wheel horsepower
Cd.........Drag coefficient
S..........Frontal Area in square feet
rho........Density of air in slug/cu. ft.
Vmax.......Speed in miles/hour.

Assume the 375 HP figure is at the crank and maybe 325 of that is
available at the rear wheels:

P = 325 hp
Cd = 0.3
S = 15.8 sq. ft.
rho = 0.002378 slug/cu ft. (standard sea level density)

Assuming ideal gearing, the above formula yields an approximate maximum
of 216 MPH which is in the ballpark. That's quite a low HP number to
run that speed and is a product of a relatively low drag coefficent and
a small frontal area. Perhaps the original GT40's weren't so bad
aerodynamically after all. Even as the cars got more draggy, top speeds
went up and lap times went down. The Ferrari and Chaparral competition
had better power-to-weight ratios but it appears Ford had a better
handle on the aerodynamics and handling.

Note that the above formula makes the implicit assumption that all
drag is aerodynamic and therefore varies with the square of velocity.
In reality, things like rolling resistance vary to a power less than 2.

> When it finally made it to a wind tunnel, they found that the complex
> "airflow managment systems" i.e. scoops and ductwork, consumed more
> than 100 horsepower. The drag coefficient of 0.43 would not suprize
> me.

Aerodynamic drag is proportional to the square of velocity and is
defined as:

D = Cd * A * (rho * V**2)/2

where:

D = drag
V = velocity
rho = air density (a function of temperature and altitude)
Cd = drag coefficient
A = area

From the above, for the early GT40 MKI at 200 MPH, we have a total drag
force of 488 lbs. The references from the day quote a frontal area of
15.8 square feet for bothe the MKI and MKII GT40's. A rationality check
on this number can be obtained by multiplying the height (40") by the
track (57"):

A = 40 inches * 57 inches
= 15.833 square feet

so we're in the ballpark.

Long Reply (Part 2 or 2)
 

Plugging in the numbers and doing the unit conversions, noting that:

1 slug = lbf * ft/sec**2 (needed for doing the conversion factor)

Yields:

Cd = 0.30 for the MkI GT40

That's in a clean configuration with narrow tires. As the original
design evolved a variety of scoops, ducts, spoilers, and vertical
stabilizers were added or enlarged, and tire width increased. It's
quite possible that later GT40's had Cd in th 0.43 range.

> Seems like I read somewhere that the Pantera (in it's original non-flared
> fender/giant wing etc) form has a drag # somewhere around .27

I show a 1972 Pantera Pre-L as having:

Cd = 0.34
A = 18.23 square feet
Cd * A = 6.20

The Pre-L Pamteras had the chrome bumperettes and narrow tires. The later
L models had the rubber safety bumpers and may have been a bit slicker.
GT5-S had the Countach-like wings and flares. Those would have considerably
higher drag as well as larger frontal area.

Understand that testing a model and testing a full size vehicle in a wind
tunnel with a rolling road surface are likely to give to very different
drag numbers.

> Mike, I have a Pantera GT-5 and that wing really does use the wind. My
> hatch opened up at about 50 and the gas shocks shot it stright up. Pulled
> up to a buck twenty on the speedo and it not only pushed the hatch down,
> but at 140 it clicked it back shut.

Most Pantera wings are primarily cosmetic. The way they are attached,
they would bend the decklid if they produced meaningful downforce.
The reason your wing (and the decklid) pushed the hatch down is because
it was at negative angle-of-attack. Even a flat plate will generate lift
(or downforce) if it is inclined relative to the air flow.

> Doc Stenhouse, I would be interested in the aero-comparison of the GT-40
> and the Pantera... while the '40 looks sleeker, the Panty does look less
> "busy" in the wind.

Ford actually had both in the wind tunnel plus a Boss 302 Mustang.
The results were published in an Italian design magazine called
"Style Auto" (Issue #29). The results were in terms of kilograms and
kilometers per hour but I've converted the numbers to pounds and miles
per hour below:

Vehicle Speed Speed Lift Lift Lift Drag HP required
(KPH) (MPH) Front Rear Total (Kg) due to drag
(Kg) (Kg) (Kg)
-----------------------------------------------------------------
260 162 136 51 187 252 238
225 140 104 39 143 193 159
Pantera 190 118 77 28 105 142 100
160 99 52 22 74 99 58
130 81 34 15 49 63 30
-----------------------------------------------------------------
260 162 120 -14 105 231 217
225 140 92 -11 81 177 146
GT40 190 118 68 - 8 60 130 92
160 99 44 - 5 39 91 54
130 81 27 - 3 24 60 28
-----------------------------------------------------------------
260 162 254 -75 179 344 324
Mustang 225 140 194 -57 137 263 217
Boss 302 190 118 143 -42 101 193 137
160 99 99 -29 70 137 81
130 81 60 -19 41 89 42
-----------------------------------------------------------------


Vehicle Speed Speed Lift Lift Lift Drag HP required
(KPH) (MPH) Front Rear Total (lb) due to drag
(lb) (lb) (lb)
-----------------------------------------------------------------
260 162 300 112 412 556 238
225 140 229 86 315 426 159
Pantera 190 118 170 62 232 313 100
160 99 115 49 164 218 58
130 81 75 33 108 139 30
-----------------------------------------------------------------
260 162 265 -31 234 509 217
225 140 203 -24 179 390 146
GT40 190 118 150 -18 132 287 92
160 99 97 -11 86 201 54
130 81 60 - 7 53 132 28
-----------------------------------------------------------------
260 162 560 -165 395 758 324
Mustang 225 140 428 -126 302 580 217
Boss 302 190 118 315 -93 222 426 137
160 99 218 -64 154 302 81
130 81 132 -42 90 196 42
-----------------------------------------------------------------

The article was about the Pantera and the photos show the original
prototype (a so-called pushbutton Pantera) setting visually level
on about 8" of of individual load cells in the wind tunnel. Few
details were given about the GT40 and Boss 302 Mustang. Given the
rear downforce, I would guess it had the pedestal mounted rear wing.

> is there a point where the downforce is "too much" thus reducing top
> speed potential?

Absolutely. Any downforce generates drag, just as any lift does.
In circuit racing, most teams will trade drag for downforce as long
as it results in a quicker lap time.

> Anyway it is just me carrying the Avanti torch since they have always
> injustly been left out of the discussions about american cars and
> speed. Especially in the circles of people my age.

Not to mention the Raymond Loewy Studebaker Starliner. Often seen
at the Bonneville salt flats due to the streamilned shape.

> Based on Ford's claimed top speed of 195 mph for their new Ford GT,
> the drag coefficient works out to be around 0.38.

That assumes ideal gearing and a drag-limited top speed.

> From this data and some rather complex mathematics, I calculate the
> drag coefficient to be 0.29. (referring to the Cobra Daytona coupe)

What assumptions did you make about the rolling resistance and power
to the rear wheels versus flywheel power? I have some of the old German
equations for rolling resistance but those were developed around very
different tires than are used today. I had a more recent NASA paper on
rolling resistance but I can't seem to locate it.

> If that is the real drag coefficient on the original Daytona, it is just
> another testament to the great skill and intuition of Pete Brock. That
> guy deserves a lot more credit than he gets. A true genius.

Brock was (and is) a great designer but he was relying on more than just
intuition. He has publicly stated his design for the Cobra Daytona coupe
was influenced "by some obscure German papers written by Wunnibald Kamm."
Kamm was one of several researchers who in the 1930's were looking for a
way to make a practical low drag shape for an automobile. In the early
1920's, Hungarian engineer Paul Jaray was able to demonstrate (in the
Zeppelin work's wind-tunnel in Friedrichshafen), drag coefficients as low
as 0.2 for a teardrop-shaped automobile. While aerodynamically efficient,
the Jaray teardrops were long and not easily applied to practical shapes.
Based upon experimental research conducted on buses, Baron Reinhard
Koenig-Fachsenfeld applied for a patent on the chopped tail as a practical
alternative. At around the same time Professor Wunnibald Kamm (head of
the Automotive Research Institute at Stuttgart Technical College)
published a textbook that described a similar truncated tail. Fachsenfeld
was persuaded to sell his patent to the state and Kamm was funded to
develop the concept. Another university professor, Everling was onto the
same idea and his design was among those tested by Kamm. Kamm's research
showed that a properly truncated tail had only a little more drag than
a full teardrop tail.

This truncated tail is what Brock applied to the Daytona Cobra. Brock
is reported to have told Shelby that it would take four times the
horsepower to go 200 mph than it would to go 100 mph. The point was it
would be better to reduce drag than increase horsepower. In reality,
it takes 8 times the power to double the speed (drag is proportional to
speed squared but the power required is proportional to velocity cubed).
I don't have the original article by Brock where he mentions this but
I wouldn't be surprised if he got it right and was referring to drag
and not horsepower.

Dan Jones
Boeing Aerodynamics and Flight Controls
1974 DeTomaso Pantera L

Good, if not lengthy stuff!

I was impressed to see the article comparing the '97 Viper against the 289 Coupe. The Coupe out performed the Viper in every area tested. 0-60, 1/4 mile, g-force on the skip pad, slalom speed and braking distance. They didn't test top speed, all though we KNOW the Coupe was capable of at least 180 mph. Simply amazing for such an "old" race car compared to a "new" at the time Viper.

Ernie

Dan,

Excellent post. Good data presentation. More of this stuff is needed here.

You might find Mulsanne's Corner interesting.

They have very good articles on current sports car as well as old and the aerodynamics therein.

One story on the Pantera. We were at the Savannah race track in the early days (1972) for a SCCA National with our March 712's. Somehow, one of our works drivers (Kevin Clower) got Ford to lend him a new Pantera for the week. Of course we drove the hell out it and had a lot of fun.

However, Sunday morning on the way from the motel to the track, I was driving the car and of course feeling my oats.

We were driving the main road from the motel (I do not remember the number etc.) and this road had an easy bend to the left and the turnoff to the main road to the track was a “Y” sort of thing. Maybe 20 degrees off the main road.

I had my foot in it and we were traveling along at about 120 mph when we reached this turnoff.

Well, I turned the wheel and we continued along in a straight line. Did not make the turn, and we ended up driving through the field between the two roads. (Luckily, the field was flat and no damage was done other then filling the radiator area with Georgia grass.)

There was a bunch of front lift in that car. Enough that it would not turn at 120 mph. We were quite careful with this car from then on.

Plus, Kevin refused to ride with me again in anything other than the transporter. He was a bit of a pu**y in some ways.

PS: I think that you need to use the width number instead of track on the GT40. 72 inches is the number on the car you are looking at.

> Excellent post.

Thanks.

> Good data presentation.

The forun software removed all the multiple spaces which really screwed up
the tables but if anyone cares, they should be able copy the data to an
editor and align the columns.

> You might find Mulsanne's Corner interesting. They have very good articles
> on current sports car as well as old and the aerodynamics therein.

Thanks for the link. It does look interesting.

> There was a bunch of front lift in that car. Enough that it would not turn
> at 120 mph. We were quite careful with this car from then on.

Wow, that's the lowest speed I've seen for someone having a front lift
problem in a Pantera. That usually doesn't crop up until considerably
higher speeds but most owners have corrected Ford's ride height changes
which probably contribute to the problem. Ford installed one inch tall
spacers in the coil-overs to meet minimum bumper and headlight heights.
They also got scared and dialed in a bunch of understeer via alignment
settings and a smaller rear sway bar. Most owners remove the spacers,
add a Euro-GTS rear bar, and re-align. A better solution is to go to
ride-height adjustable coil-overs and dial in a little rake and add a
front blade type spoiler. Makes a big difference to front lift.
A couple of Swedes ran their stock body Pantera to over 200 MPH at
Bonneville this year with only a few degrees of rake and a front spoiler.

> Plus, Kevin refused to ride with me again in anything other than the
> transporter. He was a bit of a pu**y in some ways.

Heh, heh, heh.

> PS: I think that you need to use the width number instead of track on
> the GT40. 72 inches is the number on the car you are looking at.

I thought about using that number but it's the maximum width and the
GT40 is slope sided with the sides canting in towards the narrow roof.
If you take a head-on shot of a GT40 and draw a box the width of the
front track and the height of the roof, it's a closer approximation
of the actual frontal area. In any case, I was just using it as a check
on published frontal area numbers.

Dan Jones

the moon was shinning the ....
 

Daniel,

Don't you imagine it probably was the georgia moon had been shining the night before and made the road a little slippery from the remaining dew that morning....

grumpy

Re: the moon was shinning the ....
 

Grumpy,

Please rest assured that I know what Aero understeer is. If the road had of been wet I would have stated so.

The bottom line is that this particular Pantera had severe aero push at anything above 120 mph.

Please note Daniel's reply:

Wow, that's the lowest speed I've seen for someone having a front lift
problem in a Pantera. That usually doesn't crop up until considerably
higher speeds but most owners have corrected Ford's ride height changes
which probably contribute to the problem. Ford installed one inch tall
spacers in the coil-overs to meet minimum bumper and headlight heights.
They also got scared and dialed in a bunch of understeer via alignment
settings and a smaller rear sway bar. Most owners remove the spacers,
add a Euro-GTS rear bar, and re-align. A better solution is to go to
ride-height adjustable coil-overs and dial in a little rake and add a
front blade type spoiler. Makes a big difference to front lift.

I vote for "faster than the GT-40"!
 

Like many of you, I've had the pleasure of sitting in and looking over the SPF Brock Coupe too. It made me feel like an astronaut sitting in the space shuttle.

Given all the higher tech suspension and engine parts, as well as current year aerodynamics, I will simply guess that the Coupe will out run the new Ford GT-40, and leave it at that.

After hitting ~ 130 in my roadster in 4th gear (out of 5), I think that the further improvements in the Brock Coupe, over the roadster, look to be worth at least another 70 MPH with the Roush engine and 6-speed running at the max. :JEKYLHYDE


..but then, what do I know!

All the best ladies and gentlemen.:D

Brock Coupe Top Speed
 

So far the top speed on the new Superformance Coupe has all been speculative...That is until a few days ago. A recent communication with Superforamce's test driver, Jeff Blanford, indicates that the coupe went 206 MPH in streeet trim, just as predicted by Mike Stenhouse's calculations in a recent post. The speed was confirmed not on the Coupe's 160 MPH speedo' but by using GPS on a special section of unused hiway set aside for such tests.Congrats to Jeff for being the first to exceed 200 MPH in the new Coupe. Blanford's only comment regarding the speed was "that the car feels very stable, but the road does tend to look a bit narrower once you get over 190!" Badger

That calls for a "HOLY CRAP"!
Way to go!

boy, am i feeling all smug and cocky. In a post of mine to this thread a few pages ago, i suggested the Brock/Superformance Coupe with the present engine, i believe one of the Roush 402 motors, would go "205-207 mph."

And now to hear that it went 206 mph, just makes me look brilliant.

By the way, i can only think of a few non-race cars today that, off the dealer's lot, can go over 200, much less 206, in the USA.

Lets see, not the Vipers, not the fastest 'Vettes, not a Modena, perhaps the 575 Maranello, the new big Lambo, and maybe the Turbo Porsche's.

So this goes in a pretty select and rarifed group. And this with a very streetable Roush. With better heads, and better carburation, perhaps 210 mph??