Verviticas

200mph top speed, l98 700r4 with 3.27, and 25.7" tires

Top speed (6000 rpm, obviously i dont take it there often in tpi form)

acording to the math in the calculation section of the thirdgen.org home page...

but theoretically, according to these number 200mph is the top speed of this combo? (assuming i had enough power to push it and the valvetrain survives ect...)


if so....these are fast cars......

Verviticas

I ask to confirm because i have a set of watermarks that i wish my car to achive by the time i finish it.

one of them is 200mph+....another is a 1.0+g skidpad....100' or less 60-0 braking ect... 0-60 below 4.5

and several other marks im too lazy to mention

ShiftyCapone

iTrader: (7)

You are going to need over 600hp to see anywhere near 200mph in these cars.

Most cars have the gearing to theoretically reach 150+ mph. However, just like every vehicle that travels in a fluid they are both power and drag limited which prevents them from reaching those speeds.

360Iroc

have had my car over 150 at 4200 rpm i can turn 7000

RebelRacer

just cause you can turn 7000 in 1st doesn't mean you can in 3rd...

paul_huryk

Wrong... 500hp will get you there if the car is geared right. If you clean up the aerodynamics, 400hp might even do it.

ShiftyCapone

iTrader: (7)

If the new ZO6 with less frontal area and better aerodymanics will barely tickle 200, then a 3rd gen with 500hp will have a hard time getting there. Because I am too lazy to figure it out on paper I wouldn't say either of us is right or wrong until someone shows us that is has been done. A tremendous amount of power is needed to go from 170 to 200.

RB83L69

HP requirements increase as the CUBE of the speed change, once you get past a certain speed (which you will be). That means, once you get past that certain point of fluid dynamics, then in order to go twice as fast, you have to have 8 times the HP. Those of use that also deal with the design of boats and airplanes are intimately familiar with this.

That doesn't even begin to account for the problems with the car's stability; or whether there's a road long enough wherever you are to even get close to the HP limit.

The aerodynamic limit of one of these cars in anywhere near stock trim, using typical stockish HP values (we're talking 250-300 HP here) is somewhere in the 140-145 range. Anybody tells you they've had their car faster than that, is either lying, or has considerably smaller tires on their car than stock, or their speedo is otherwise wacked. Going from 300 HP to 400 HP at teh RPM the engine will be running at when doing this experiment will get you about 7-8 mph typically, with no body changes.

This of course assumes optimum gearing, such that at the speed of interest, the engine is running at the RPM that produces peak HP. So some TPI car that makes peak HP at 4400 RPM and craters above that, is going to have a real tough time even making to the aerodynamic limit; and sure as hell isn't going 200 mph at 7000 RPM. It won't be an issue.

Among these cars, the ones that have the lowest aero drag (and therefore run into the HP cubed limit the latest) are the early Firebirds followed by the IROCs. Cars that "look" sleek, often aren't. A Lamborghini Countach, for example, has the approximate aero properties of a brick wall.

Many, if not most, cars will go faster in some other gear than their top-most one. 6-speed cars and cars with grocery-cart gears like low 3s are particularly prone to this.

Most people's monkey-spank about "top speed" is just that: monkey spank.

pvt num 11

They're right, aerodynamics and the drag coefficient matters a lot when speeds get higher. Bonneville salt flat runs are done with some seriously modified cars, the '91 and '92 Firebirds are used sometimes becasue they have a lower Cd then other third-gens. One article (yeah, articles can sometimes lie, I know) stated that some were using the GTA's aerofin becasue it actually works well at those kinds of speeds. I wish the fin would not fall apart and rust mounting brackets, though... crummy GM engineering...

Shaving side mirrors, pushing the tires out so there's no 'gap' between the body and the tires (when viewed from above), lowering the car, and installing a belly pan would all be really really helpful to achive the Cd you would need to see anywhere close to 200 MPH. A stock car is NOT going to see this sort of speed, not anywhere close, without a lot of body work and some serious horsepower. I'd be really lucky if my TTA would ever see 150, if I had the place to try this, and I don't. Weight is not a bad thing, contrary to 1/4-mile logic, weight is free downforce, which is a very good thing. A car's aerdynamics begins to do some pretty voodoo-magic things once you get going really fast. The typical Uncle Ben's double-decker wing is pretty much useless at the speeds they see, except for pushing the car through the staging lanes to keep the motor cool between runs.

I hope this wasn't a lot of McDonals parking lot monkey spank, if it actually is, I'll go take my 40 lashings without complaint.

ShiftyCapone

iTrader: (7)

Thank you RB! You were patient enough to post that perfect explanation.

RWB____s

I always say. You may be "faster" than me, But by the time you catch me, I'll be in a different time zone

paul_huryk

The Z06 might only be that fast due to gearing - you can't get to top speed if your power is over peak and tapering off.

I'm not so sure about the Z06's aerodynamics being any better than a thirdgen - also not sure about the frontal area being smaller. The C4 did have a smaller frontal area......

paul_huryk

Someone knows a bit about aerodynamics here... but so do I, *** bless engineering school.

Yes, to go 2x as fast, the aerodynamic drag goes up 2^3 = 8

To go 3x as fast, the drag goes up 3^3 or 27x.

Here is my basis:

225hp = 150mph....

8.3hp = 50mph (27x)
533hp = 100mph (8x)

Now that is the combination of aero and mechanical drag, I figure (a wild guess) that mechanical drag is 83hp at 200mph), you get 450hp for aero drag. If you were to deduce the aero drag by 10%, you can lop off 45hp needed to touch 200mph.

It's all elementary, but subject for opinions.

Gearing is the 2nd most important thing (other than power and aero).

Orr89RocZ

iTrader: (20)

the Z06 has like 3.45 gears or something with that T56 six speed

it cant pull well in 6th gear and even 5th aint bad. there are tons of Vids of a Z06 topping out at nearly 180 but thats about it. i am sure 190 is possible with a 2.xx or 3.08 rear end

pvt num 11

Shave the mirrors, drop the ride height a bit, and you could see less Cd on that Z06 - but mirrors are sort of required on street cars - at least here they are.

kdrolt

I think you mean

8.3 hp = 50 mph
66.7 hp = 100 mph
225 hp = 150 mph
533.3 hp = 200 mph


An aside:

225 is 168 kilo Watts (kW)

power = 0.5*AirDensity*Cdrag*FrontalArea*(speed^3)

and Cdrag is the coefficient of drag, a number that represents the resistance of an object (a car, a sub, a plane) to fluid flow.

For a 3rdgen Fcar, FrontalArea = roughly 74 by 51 inches (a guess: using Corvair height, lower & narrower than my Caprice), which converts to 2.44 sq meters. 150 mph is 67 meters/second. And AirDensity is around 1.2 kg/cubic_meter, so everything is in consistent units.

168 kW = 0.5*1.2*Cdrag*2.44*(67^3), then solve for Cd:

Cdrag = 0.38 which is higher than the data on TGO.

But not all of that 225 hp gets to the road. For fun assume that 15% of that 225 hp gets lost in the drivetrain and wheels, so only 191 hp is applied to the road. Subbing in 191 hp (142 kW) in the above:

Cdrag = 0.32

which is pretty close to the GM published values shown at TGO.

That also means that 15% is a reasonable loss for the conditions of rpm + gearing at 150 mph. The loss will be less for lower speeds and rpms, but the loss doesn't go to zero at zero speed (static friction, mostly in deforming the tires) and the loss won't entirely be represented by the above simple math model.

FWIW, HTH from another graduated member of the college math/science/engineering ranks.

paul_huryk

Oops - I put the wrong data for 100mph - sorry about that.

The stock Cd is about .32 stock, not too bad, which means my backwards calculation is almost on the money.

Of course, you can lower that to .25-.27 if you want to clean up the stock bodywork (and some lowering). Radical aerodynamic improvements might yield a Cd in the .20-.22 range with some additional downforce. The difference from going from .32 to .25 is a 22% decrease, dropping power needed by 99hp, bringing approximate power needed to touch 200mph down to 434hp.

kdrolt

I haven't tried this, but it would be neat to back out the Cd on the HRM 3rdgen Fcar that went some obscene number above 200 mph at Bonneville. IOW how low can the Cd go?

hotrod87camaro

wouldn't you be a little scared to go that fast on the street?

88GTA383

Lingenfelter took a gta to 298 mph at bonneville with only minor body modifications. Of course he used a twin-turbo 355 that made 1400 hp.

paul_huryk

The Hot Rod that featured the Sledgehammer Vette had an article on a GTA that was built for Bonneville. The only aero enhancements were a lower front spoiler (looked almost like stock), no mirrors, and it was lowered. It ran a 650hp NASCAR motor and topped out at 238mph. If it had the 900hp of the Sledgehammer, it would have easily outran it (it went 254mph).

I think they said that car was .24 or .25 and looked almost stock (except for the lower front spoiler).

Nitsuj86Iroc

your guys' technical calculations make me excited about starting my mechanical engineering degree in college haha. im at the university of akron too, they are ranked very high for engineering.

anyway, at about what speed does aero drag become a major factor?? i know it always is a factor, but at say, 70 mph, is it much drag?

KiLLJ0Y

iTrader: (1)

better get a good set of hood pins and find a way to close up the head light pockets..

paul_huryk

Believe it or not, unless you take a specific course on aerodynamic, you won't hear all that much about it. Fluid mechanics does come close in theory though. You might want to pick up a few books on the subject as they will cover a lot more than any undergrad course ever will.

Aero drag really becomes a problem depending on the vehicle. for instance a 18 wheeler might have a bad aerodynamic shape, but it needs most of its power to move its weight against gravity, even at top speed. Whereas a car might not.

As you get to really high speeds (over 300mph), tire friction becomes a major power eater - I heard that Al Teague's Bonneville streamliner has more tire drag at 425mph than aerodynamic drag.

Then you can talk about motorcycles, which have awesome power to weight ratios, punch a very small hole in the air, yet are a lot slower than cars that can accelerate at the same rate. This is due almost all to bad Cd since vehicle weight is so low.

I'm a grad of NJIT- NJ Institute of Technology (2x)

kdrolt

I'd say the most useful courses would be

A. Calculus I (differential)

B. Physics I & II

C. Fluids I

and the Physics sequence is probably the most universally useful and applicable. You'll get all of these within the first 2 years of school.

You'll have to take Calc I-II-III and Physics I & II as part of your curriculum, and you'll probably have to take Fluids I as part of the ME curriculum. It's not likely that you'll ever see an automotive-type aero question in any of them, but if you think about the problem and use what you had in the above (after you've taken them) you'll be able to apply them just like using specific tools. If you are lucky, and since Akron is close enough to Detroit, then there may be an automotive-specific upper division class you can take within the ME dept, and it's highly likely that there could be an aero class (also upper div in the ME dept) because of Akron's proximity to things aero in the State of Ohio. I'm sure you can find all of this on the UofAkron website.

It's hard to answer the aero drag question; the right way to answer it would be to have a model for the (internal) frictional drag on the car and then set it equal to the aero drag formula and then solve for the unknown (speed), i.e. where the aero drag equals and then exceeds the aero. From a handwaving viewpoint, I'd say somewhere above 30 mph based on the kid's stuck-hand-out-window method of data collection.

FWIW also from an ME when I was an undergrad.

Nitsuj86Iroc

Cool, Akron does have specific classes such as vehicle dynamics and areodynamics because they participate in the FSAE competition. its like a mini formula car haha, restricted to a 70 HP crotch rocket motor, and its quite high tech, nearly as much as a pro race team. anyway there are things that get pretty into those topics

ShiftyCapone

iTrader: (7)

I found fluids, heat transfer, and engineering analysis to be the most helpful when dealing with automotive stuff. Most aero courses are grad courses and or 4th/5th year electives. Luckily when I was at UD (University of Dayton, Ohio) they had IC engines and Vehicle Performance analysis grad courses that undergrads could take. They were great courses and we had plenty of Delphi scientists teach us mind boggling stuff. I would have loved to take aero but I simply could not fit it into my course work and I wouldn’t take it above IC engines and VP analysis. Every engineering course you take though can be applied to the automotive realm. It is just great in that regard. There are some amazing auotmotive engineering teachers in the state of Ohio.

Dirtbik3r

haha. You mean to tell me that other colleges take engineering analysis besides mine? We're doing the course /w excel and vba programming too though.

Currently an ME undergrad who wants to become a mechanic .
-Transfering to Suny Morrisville for Automotive Engineering Technology then possible off to MIT for a masters in automotive engineering. I'm just not liking what ME is getting into at this college.

ShiftyCapone

iTrader: (7)

Chances are you won't like it until the switch kicks on and you can apply it to every aspect of how life works. You can then choose cars, planes, etc etc. The science is the same.

kdrolt

If the school you are at is small, then the ME curriculum will be pretty general especially at the undergrad level. In some respects the burden gets placed on you to fill-in the parts that are lacking/uninteresting with what I used to call creative course selection, and then getting the Assoc Dean or Dept Head to accept it as one of the valid engr/science electives that you need in an ABET accredited undergrad engr track. IOW if you make a compelling argument for taking something considered non-traditional, they'll usually allow it. And you'll get a lot more out of your otherwise bland course track.

FWIW MIT doesn't have automotive engr as a separate major for any degree -- though they do have it within a research group under the ME umbrella per the Sloan Auto lab. So you can do automotive-type grad work but you'll get a master's in ME. If you get serious about this you can PM me about it.

smokeingGTA

I have heard that the tta hit 175 at indy in stock form. I can't say if it is true. I know a guy that had his at 150 stock but did not push it any more. those motors made a little over 300 hp but they were a little lighter due to the fact they were only 3.8 turbo motors. Does anyone know the weight of the tta's? If you have the time and the money you can make it happen.

Dewey316

I'll throw another thing to think about. Typically the lowest CD is achavied height is actualy raised. IIRC about .125 of the wheel base is ideal. that number gets better the better the flow can stay attached under the car, with a good belly pan and diffuser, and well planed venturi tunnels under the car, etc, you can get better aero's at a low ride height. Of course, this will also help the anti lift, this may or may not be a good thing when trying to go for 200. you would probably want to tune it, to keep the seperation from happening under the car, but keep from creating large amounts of downforce.

paul_huryk

The idea of raising a car for better CoD is a novel one, as the downforce will be reduced and lift will occur. For years, Bonneville guys with stock bodied cars had the bright idea of adding weight to counteract the lifting forces of having marginal (or even bad ) aerodynamic problems. Those guys then had major problems finding tires that could keep together at 200+mph at 4500lbs. Some people died in crashes from overloaded tires that failed. The real solution is to tweak the aerdynamics to reduce drag without adding lift (or downforce for that matter). You don't need a car that can produce 2g's of cornering at 200mph is its never going to turn. Its all a balancing act.

Dewey316

lift is actualy lowered and so is the CD with the raised height, on most production type car bodies. It has to do with the boundry layer in relation to the ground. if the seperated airflow doesn't meet the ground while still under the car, there is less drag. When I get home, i'll pull out the comp. car downforce book, and the FD book, and post the actual text with the numbers in context for you.

smithtc

iTrader: (5)

A bit late...but here's a little Bonneville info...taken from a post I made on another forum... I think is relevant.


If you play with the math you will come to find out that the power to overcome aerodynamic resistance increases with the cube of velocity indicating, for example, that 8 times as much power is required to overcome aerodynamic resistance if the vehicle speed is doubled; therefore, it's clear that resistance will increase rapidly at higher speeds. More reason to argue the point that Gale Banks, Don Stringfellow, and Bruce Geisler who worked with Bob Dorn (Pontiacs Chief Engineer) and John Schinella (Pontiacs Chief Designer for the Exterior) in the early to mid 80s did not take a stock car, stuff a high power drivetrain in and go racing, leaving a high percentage of Free Horsepower on the table in terms of decreased Aerodynamic resistance. They are actually a BIG reason the drag coefficient of the STOCK car IS 0.31-0.33. And the cars they used on the salt flats were lower than 0.30 (Sorry, don't have their exact specifications). I do have Karl Steggemeier's and Gary Eaker's car...1988 TA...that they took from stock form, 0.33 Cd as measured in GM's wind tunnel, and brought it down to 0.20, as measured in GM's wind tunnel. And from an untrained eye, their car appears more "stock" than what Banks had. As far as the 91 TA mentioned...I was wrong. It was Steggemeier and Eaker that discovered the 91 would lift. They tried to fix it by adding 500lbs of ballast. His car still flew. So, no need to encourage stock bodied 91, 92 owners to try some high speed tests on the interstate.

Some info found on "thirdgen.org"
Top Speed is also an energy argument:
Neglecting potential energy (you're not going up or down a hill) the total energy of the car is 1/2*m*v^2 where m is the mass and v is the velocity. So, every time you double the velocity, you quadruple the (kinetic) energy. You need to dump in 4 times as much energy from the engine every time you double the speed. So, since you're car can't quadruple it's energy output every time it doubles it's speed you will accelerate slower. No doubt that wind resistance and other variables are a factor, but even in a vacuum you would not be able to maintain constant acceleration due to the increased energy needs.

kdrolt,
The 0.397 Cd I came up with for my car on another post was based on some guesswork...not worth comparing to anything other than back to back tests done "in-field".

3.8TransAM

89 TTA's were clocked in the low 170 on the stright at INDY and they were stock prodcution cars with no modifications performed.

Mine has seen 145(buried it just past the 145 tick)

At 100mph u need 1psi boost, at 145 I was running steady at 6psi boost. Had roughly 10-11 more psi available and about a qrtr gas pedal left :-)

Yes I am stupid, but the cars certainly did fly :-)

Common opinion on making a 200mph street car affordably(relative statement) is to clean up a F-body aerodynamically and gear it right with 500hp in it and go for it.

So theoretically, now that my TTA makes somewhere in that realm of hp. Would it happen with stock gears?

(i think any f-body not gone thru thouroughly would make me mess myself at those speeds)

later
Jeremy

CrazyHawaiian

I did notice that I can never get my 91 Z28 to go much faster than pegged (145) even if I kept going. I dont remember what RPM's I was hitting right when I pegged it but I was boosting 6psi and I kept going. It did kinda feel like I hit a "wall" so to speak and the car was no longer accelerating as fast. I wondered if it was the tranny or valve float, now I should consider aerodynamics. Kinda supports what RB said. But I guess it didnt matter because the guy I was racing blew by me going like 10 or 20 mph faster