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I really don't know how to reply to this anymore

Old 10-01-2010, 01:33 PM
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Originally Posted by drmatera View Post
I really don't know how to reply to this anymore
That usually happens when someone boxes themselves into a corner. (JK) All joking aside, I would still like to see the two gladiators face off in a top speed run. Maybe we can convince Gabe to pull the rockers off in the interest of more areo. All in fun.
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Old 10-01-2010, 01:46 PM
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really? you honestly think lots of down force and big wings make a car go faster top end. I would love to hear your theory on this. Better yet i'm sure every auto manufacturer in the world would love to hear it as they most be going in the wrong direction in their quest for "low drag" vehicles for better fuel economy (for cutting thru the air more efficiently) and using less fuel (because it takes less power to push a "low drag" vehicle down the road). Nascar would love to remove their wings for better top end but the "drag" that holds them down around the corners is a neccesay evil so they sacrifice the top end speed for stability in the turns. And Top fuel dragsters use wings to push the car down and keep traction which slows them down aerodynamically. The fastest cars at the salt flats are shapped like bullets with as little downforce as possible to reach those high speeds...

I am all ears
Old 10-01-2010, 02:16 PM
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Old 10-01-2010, 02:17 PM
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The yellowbird was based on a narrow body 911 because the 930 body shape had more drag which limited their top speed. Ofcoarse RUF is full of shlt too i suppose
Old 10-01-2010, 02:18 PM
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Quote:
Originally Posted by drmatera View Post
really? you honestly think lots of down force and big wings make a car go faster top end
Quote:
Originally Posted by drmatera View Post
. I would love to hear your theory on this. Better yet i'm sure every auto manufacturer in the world would love to hear it as they most be going in the wrong direction in their quest for "low drag" vehicles for better fuel economy (for cutting thru the air more efficiently) and using less fuel (because it takes less power to push a "low drag" vehicle down the road). Nascar would love to remove their wings for better top end but the "drag" that holds them down around the corners is a neccesay evil so they sacrifice the top end speed for stability in the turns. And Top fuel dragsters use wings to push the car down and keep traction which slows them down aerodynamically. The fastest cars at the salt flats are shapped like bullets with as little downforce as possible to reach those high speeds...

I am all ears
I never said they did..In fact all I did was respond to a comment you made:
a top speed run would not be good for a car with lots of downforce bodywork. Eddie's sleek narrowbody with shaved drip rails and 997 headlights has much less frontal area.

Its somewhat of an incomplete point. What is the true meaning of your comment? Will Blackbird be unable to achieve a top speed greater than Bellos due to its body panels? Will the panels limit the car to a specific top speed? If so, what is that speed and it be lower than the 964? How are you coming to this conclusion? Thats all I'm really talking about, not a debate over the science of aerodynamics. Remember, these are not salt flat cars. They both need a combination of areo and downforce for stability as you even state yourself. While aerodynamics are important you are making it seem like that is the only factor in the race and I simply disagree with that. Maybe when Gabe gets the Blackbird sorted we will find out.
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Old 10-01-2010, 03:08 PM
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Challenge accepted, spring 2011 drag, roll and top end in 1 mile.

Btw I'm currently geared for 254 with stock ratios. And my car is registered as a steet car that I'm driving to Cali and back...
Old 10-01-2010, 06:30 PM
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I'll travel for this......

You all have some very valid points,

downforce=drag

Not enough downforce=wheel spin @ higher speeds

Power to weight also plays into this equation

Let's not forget that the Winston Cup cars were in the 200+ mph range back in the 70's with Monte Carlo's and such.
Old 10-01-2010, 06:53 PM
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Knowing that the 935's of the 70's were capable of reaching speeds close to 230 mph with an almost identical body as that of Blackbird I have no doubt that areo will not be a major factor in this piticular race. These are two of the same breed and the differences in areo is dimunitive at best. Its not like we are compairing a 68 Roadrunner with a Lambo. I think Bello will have his hands full with a well sorted and dialed in Blackbird.
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Old 10-01-2010, 07:17 PM
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The only 935 that ever approached 230mph was Moby Dick with supposedly an honest 225mph. That car was a much more aerodynamic longtail version of the "standard" 935s of their day.
As far as aerodynamics and wings are concerned, I still get a chuckle out of the early LP400S Countach, 181mph sans wing, 165mph with optional $5000 wing.
Bello's car is in a league of its own at the moment and let us not forget that its is no lightweight. I wonder what it could do stripped down. Blackbirds car is a beauty, but top end it would never stand up to Bello's low profile missile given identical horsepower. And since Bello can break 160mph in the quarter, traction above those speeds does not seem to be that much of a problem.
Old 10-01-2010, 08:56 PM
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Quote:
Originally Posted by Reaper930 View Post
Challenge accepted, spring 2011 drag, roll and top end in 1 mile.

Btw I'm currently geared for 254 with stock ratios. And my car is registered as a steet car that I'm driving to Cali and back...
when u drive to cali, def let me know if u come thru socal, id like to check out ur car if possible!
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Old 10-01-2010, 09:33 PM
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Done. And fwtiw a stock k3 can hit over 235 in 1 mile and mody dick is worth 255 in drag speed...seriously study you specimens
Old 10-01-2010, 09:49 PM
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drag is so important for top spedd runs that my money would be on the Non downforce generating car. 232 is pretty insanely fast in the standing mile.

There is only one way to find out though......run the test.
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Old 10-01-2010, 09:51 PM
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Oh, since your doing all straight line stuff, why not do some hot laps on a road course? might be interesting to put a category in there to FAVOR downforce, and not just slippery Drag Coefficient style tests.


Just sayin......

And BTW, I love BOTH these cars.
Old 10-01-2010, 10:13 PM
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This whole "downforce/drag won't affect top speed" argument is comedy, it makes a HUGE difference!! Gabe's car will need a lot more power than Bello's to hit the same speed, above 160mph aero plays a massive role
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Old 10-02-2010, 04:51 AM
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Old 10-02-2010, 04:59 AM
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This whole "downforce/drag won't affect top speed" argument is comedy, it makes a HUGE difference!! Gabe's car will need a lot more power than Bello's to hit the same speed, above 160mph aero plays a massive role
Again... I never said that. All I said was that a 935 type body is capable of hitting well over 200 mph so it wont be as much of an issue with these to specific cars. I'd like to hear your calculations in regards to how much more horsepower Blackbird will need due to its body pannels. Additionally, I wouldnt be so myopic in thinking that Gabe might just possibly modify or remove high resistance pieces a bit if he were to take part in a race like that? (Kind of like what everyone does) Comon guys lets think outside the box a bit.
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Old 10-02-2010, 07:19 AM
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Some good read that I just discovered: I like the last part.


Horsepower is a measure of power, which is a technical term in physics. It measures the amount of work that a force does as it acts over time. Work is another technical term in physics. It measures the actual effect of a force in moving an object over a distance. If we move an object one foot by applying a force of one pound, we are said to be doing one foot-pound of work. If it takes us one second to move the object, we have exerted one foot-pound per second of power. A horsepower is 550 foot-pounds per second. It is another one of those historical units that Napoleon hated and that has no reasonable origin in science.

We can expend one horsepower by exerting 550 pounds of force to move an object 1 foot in 1 second, or by exerting 1 pound of force to move an object 550 feet in 1 second, or by exerting 1 pound of force to move an object 1 foot in 0.001818 seconds, and so on. All these actions take the same amount of power. Incidentally, a horsepower happens to be equal also to 745 watts. So, if you burn about 8 light bulbs in your house, someone somewhere is expending at least one horsepower (and probably more like four or five) in electrical forces to keep all that going for you, and you pay for the service at the end of the month!.

All this means that to find out how much horsepower it takes to overcome air resistance at any speed, we need to multiply the force of air resistance by speed (in feet per second, converted from miles per hour), and divide by 550, to convert foot-lb/sec to horsepower. The formula is



and we get the following numbers from the formula for a few interesting speeds.

v (mph) 30 55 65 90 120 150 200
F (pounds) 14.5 48.7 68.0 130 232 362 644
horsepower 1.16 7.14 11.8 31.3 74.2 145 344

I put 55 mph and 65 mph in this table to show why some people think that the 55 mph national speed limit saves gasoline. It only requires about 7 hp to overcome drag at 55 mph, while it requires almost 12 hp to overcome drag at 65. Fuel consumption is approximately proportional to horsepower expended.

More interesting to the racer is the fact that it takes 145 hp to overcome drag at 150 mph. We know that our Corvette example car has about 240 hp, so about 95 hp must be going into overcoming rolling resistance and the slight braking forces arising from internal friction in the drive train and wheel bearings. Race cars capable of going 200 mph usually have at least 650 hp, about 350 of which goes into overcoming air resistance. It is probably possible to go 200 mph with a car in the 450-500 hp range, but such a car would have very good aerodynamics; expensive, low-friction internal parts; and low rolling resistance tyres, which are designed to have the smallest possible contact patch like high performance bicycle tyres, and are therefore not good for handling.
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Old 10-02-2010, 07:40 AM
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Here is the link for the complete read:

Part 6: Speed and Horsepower
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Old 10-02-2010, 07:44 AM
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They say that the Ruf "A" piller fillers are worth 5mph above 185mph... That is a lot of free speed for very little change. That car of Bello's is slippy as hell compared to Gabe's, i don't have figures for either car obviously, but it doesn't take a clever guy to see that with the same power in each car, Bello's car is going to a lot further down the road once you get anywhere near 200mph.
I can't wait to see Gabe's car run, it's an epic project! And i don't doubt it'll lap the ring quicker than Bello's could.... But in a straight line, with that body, it's going to need a monumental amount of spoot to keep up!!

Jean, who some of you are familiar with over on Rennlist, did a test with his 993's some time ago, here's a copy of one of his posts

"I went out with each of my stock 993TT and my GT2 bodied 993TT, and tried to measure the aerodynamic drag difference between both cars. This is a very difficult exercice as there are many factors impacting the readings so one needs to eliminate as many as possible..

So the runs were done a few minutes apart, and tried to get at the same exact point before letting go the throttle and putting it in neutral.

The measurements need to be taken at high speed as friction losses are lesser relative to aerodynamic drag. As speeds drop, tire friction and other losses become more significant.

Car 1: 100% stock 993TT with P zeros, stock sizes.
Car 2: Running weight close to 1500kgs, Michelin race full slick tires, -.2.7 camber up front, toe out 8', Gt2 wing at full downforce setting.

Method, speed up to 130 mph and then put the car in neutral. One run each way back and forth with each car, the impact of slope and wind turned out to be minimal as the slope was insignificant and there was no wind.

Car 1: 125mph - 85mph in 26 seconds and 1193 meters (around 3900 ft)
Car 2: 125mph-85mph in 18.5 seconds and 845 meters (2772 ft)

So the GT2 bodied car reached 85 mph 7.5 seconds and 1200 feet earlier than the stock 993TT !!



The big question mark is how much does that represent in terms of HP robbed?? Tough one! I did A LOT of calculations, and my findings are that at 125 mph, my 993gt2 needs around 60hp more than my stock 993TT to beat aerodynamic drag!

In terms of CDxA, based on published aerodynamic figures (circa 0.66), the drag should have robbed around 100 hp at 125 mph from my stock 993TT, wheras my datalog measurements and calculations showed me 90 hp, so I am not too far from theory. Based on the same measurements and calculations, the GT2 bodied car needed about 150 hp at 125 mph, meaning it is an equivalent CDxA of 0.9! this is adjusted for weight difference as well. Part of this is rolling resistence (alignment settings) , part is downforce rather than drag, and largest part is drag obviously. This gives an idea of how big an ennemy drag is to performance.

Next, will measure with and without GT2 wing alone, and will also measure at low speed to determine rolling resistence rather than drag.

I hope you find this useful. "

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Old 10-02-2010, 08:32 AM
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