Got my FI system tonight!!!!

[Kevin Shasteen]

Coefficients of Drag -vs- MPH, Center of Gravity-fore/aft or from side/side??? I've always avoided those chapters when reading.

 

I do have some books that talk about it-but I've never really read up on it as its not as exciting as HP/Torque, ET's Arrg Arrg Arrrg-Ohh ohh..oh yea (Tim Allen Impression on the Internet).

 

Mike, there's a book I have that deals w/how to set up your car for performance handling: specifically SCCA & IMSA. Its a Ford Mustang book but it is chock full of info-you might want to check it out the next time you're near a Barnes & Noble.

 

The name of the book is "Mustang Performance-Handbook 2" by William R. Mathis; its an HPBook & its copywrite is 1995. If you look for it-its binder is white & the title is in bright Red/has a lot of good info in it.

 

In it they have diagrams on how to check center of gravity, side to side center of gravity & have diagrams on how to build a jig which allows you to use home scales.

 

Another book I have on Auto Math talks about center of gravity & weight shifting during road racing-it says for a road racer you'll want a slight rearward weight bias as this favors better traction & thrust & claims that side to side weight distribution should be "even" for consistent cornering in either direction (which means adapting your cars weight w/the weight of the driver).

 

About Coefficient of Drag...I'm gonna have to read up on that one.

 

Kevin,

(Yea,Still an Inliner)

[Mikelly]

Kevin,

I think the original version of that book was called "SLOT CAR MUSTANG" and I have it if that is the same... This one was in binder format with black and white. Another good book on suspensio setup is "HOw To make your car Handle" and I forget who wrote it, but a White Porsche on a road course is on the cover...

 

I got my original design for Sub-frames and seem-welding from the SlotCar Mustang book...Very good info. I'll have to dig that book up.

 

Got a note back From Hennessy and they actually are running the T56 in some of their Vipers. One Viper ran two years ago and achieved 187mph with a few bolt ons and some MAJOR suspension and aerodynamic mods. Supposedly the issue with the Viper is the nose... That BIG opening is an issue and catches MUCH air. He claims that in a sub-500HP GTS Viper, without any mods, it will not push 6th gear. However, Hennessey also pointed out something we already know... That additional 600# of static weight on those cars is also a huge problem. It is much harder to move the extra weight. Hennessey told me that based on my flywheel HP, Torque (Both estimates), weight of the car, and the mods I will run on the car to clean up aerodynamics, I should be much better suited to push 6th gear, but more importantly is the fact that I'll be able to use MORE of 5th gear, which is where some of the early Vipers had even MORE trouble.

 

All good stuff...

 

Mike

[Guest Anonymous]

<snip> However, Hennessey also pointed out something we already know... That additional 600# of static weight on those cars is also a huge problem. It is much harder to move the extra weight. </snip>

 

I seem to recall a Motor Trend (or Automobile?) top speed test a few years ago, and they pointed out that weight has no effect on top speed, just how long it takes you to get there... Was I misinterpreting your words Mike? Looked like Henessey was saying a heavy car won't go as fast as a lighter one...

 

Of course, if you run out of road to HIT your top speed, then weight becomes a factor... But in the Silver State, I don't see that as being a problem...

 

The other thing I saw: 4850rpm to hit 200 mph... I'd think you may want to mess with gearing or something to bring 200mph closer to your HP peak... or maybe you won't need to! You may just crash through 200mph with the car yelling "BRING IT ON" in its best small-block wail!!

 

Mike, wanna adopt a 26 y/o?? I will turn wrenches for food (and rides)

[Kevin Shasteen]

Okay Mike-this is what I've learned after a nights worth of reading on Areodynamics (jury is still out on some of it).

 

The issues are:

 

1) Areodynamic Drag at High Speed

2) Induced Downforce (tail wing?)

3) Lift/Drag Ratio

4) Absorbed HP as a result of drag

 

The areas where we'll have to concede are that we dont have a dyno print out of your car therefore we dont have actual #'s for each 200rpm increase for torque/hp; nor, do we know what your Coefficient of Drag "Cd" is..so we'll have to guess in those areas.

 

What we can/do know is the frontal area of your car (you take the measurements); we know what your car did in the 1/4 mile from an earlier posting on HybridZ-this will give us hp/torque at that specific MPH/RPM, we know what MPH you'ld like to reach and we know the gearing. After reading all that I did last night-I agree w/Hennessey's sumation-your Areodynamics are gonna be extremely important.

 

Here's what I've come learned:

 

One book I have gives these Cd's (Coefficient of Drag) numbers:

 

1)1.2 = Cd for A barn door "as a reference"

2) .44 = Cd for a VW Beatle

3) .35 to .45 = Cd for a Typical Modern Sedan

4) .31 = Cd for a Winston Cup Car a few years ago

 

*NOTE: I think its safe to assume your car's Cd is somewhere between .31 & .35

 

The formula for Drag"hp" absorbed is:

 

Where:

Drag"hp" = HP absorbed due to drag

Cd = Coefficient of Drag

A = Frontal Area in Sq.Ft.

V = Velocity, mph

 

Drag"hp" = ((Cd x A x V^3)/(15 x 10^4))

 

This book also explained how to figure "A" frontal area for Areodynamic formula: take .80% of the height of your car from the front view (as if you're looking at your car while standing in front of it) & multiply that times the width of the car's frontal view.

 

I dont know your car's frontal area since you've changed front end clips; but I measured my 78Z 2+2 & it measured 49"H x 60"W; so .80% x 49"= 39.2" & remember we need sq.ft. not sq.in. so we have to convert our measurements like this: 39.2 x 60/144 & this gives us 16.3 sq.ft. Frontal Area.

 

Take the formula for Drag using Cd of .31:

 

Drag"hp"= ((.31 x 16.3 x 200^3)/(15 x 10^4))

 

Drag"hp"= 40424000/150000

 

Drag"hp"= 269.49hp

 

That's an awful lot of hp loss due to drag. There was another formula the book gave to determine what peak "MPH" would be using the same numbers above; in this formula you have to transpose #'s w/in the formula-it is as follows: BTW-I'm using your 469RWHP from your 1/4 ET=128mph at 5683rpms (rounded to 6000rpms).

 

Where Khp = Known RWHP

 

Khp = ((Cd x A x V^3)/(15 x 10^4))*Drag"hp"

 

remember to transpose (multiply both sides by 15x10^4)

 

((469hp x 15 x 10^4 = .31 x 16.3 x 200^3)

 

Transposing still (swap sides to get V^3 on the left side)

 

V^3 = ((469hp x 15 x 10^4)/(.031 x 16.3))

Tranposing still (divide both sides by .31 x 16.3)

 

V^3 = 13922422.32

 

V = Cube Root(13,922,422.32)

 

V = 240 (theoretical mph)

 

*NOTE=Remember I used the Cd equivalent to a Winston Cup car; now lets go w/the Cd of .34 (just under the Cd of a modern Sedan. If we used a Cd of .34 this would give us a top MPH speed of 233mph.

 

So using the Cd's of .31 & .34 we find a top MPH speed of:

 

1) Cd .31 = Top MPH/240

2) Cd .34 = Top MPH/233

 

This all falls on assumption of your Cd & if you have the torque at the appropriate rpm's.

 

The driveshaft torque at your 1/4mile ET based on your 1/4mile HP of 469hp is:

 

Torque = 5252 x HP/RPM

 

Torque = 5252 x 469/6000

 

Torque = 410ft.lbs

 

Your T56's 6th gear is .5ratio; multiply the ratio times the 410ft.lbs (assuming a .90VE)

gives us:

 

410/.90VE = 456ft.lbs*.5 = 228ft.lbs of torque being applied at the rear wheels at 6000rpms...you only need 4844rpms to reach 200mph; so the variables, actual torque, actual hp & actual Cd are going to determine you reaching your objective. (Well Duh!)

 

What kind of rear wing are you running (Length x Width); Remember that any -Lift (Negative Lift) will aid traction & reduce drag which will aid in your top mph speed; upto a certain point (I cant believe I just said that-it actually sounds half way intelligent/My head hurts)

 

 

Whooo; boy that was a mouthful-but I enjoyed every bit of it.

 

Kevin

(Yea,Still an Inliner)

 

[ June 12, 2001: Message edited by: Kevin Shasteen ]

[Drax240z]

I see Kevin beat me to it, going to edit this a bit.

 

"how to make your car handle" is written by fred puhn. Highly recommended by everyone I know thats read it. Very practical examples and descriptions, combined with the formula's if you want to get technical.

 

A little of drag coefficient. (where is michael anyway? )

 

Force = -1/2*(density)*(velocity)^2*(Drag coefficient)*(Frontal Area)

 

Air density is generally assumed to be 1.2kg/m^3. (you US guys should learn metric) Heh.

 

So at a theoretical 1.2kg/m^3 density, Cd=0.44, frontal area 1m^2, velocity of 200mph (320km/h) the force from drag is:

 

= (1/2)(1.2kg/m^3)[(88.9m/s)^2](0.44)(1m^2)

= 2086.45N

 

= 469lbs force drag at 200mph.

 

At 100mph:

 

= 119lbs force drag.

 

Now these numbers may be low or high for the z, I am not certain the Cd is 0.44, I think it was. And I've assumed the frontal area is 1m^2. Kevin's estimate of 16.2ft^2 is more like 1.5m^2, so multiply my results by 1.5 to increase accuracy.

 

One good way to measure frontal area. Take a front profile shot of your car on your digital camera, with a meter stick for reference. Print it out and carefully draw a uniform grid over the whole picture. Add up the areas of each grid. (its pretty easy to estimate 1/2 or 1/4 of a small grid)

 

I wish I was taking fluid mechanics now, but I'm still a newbie at this stuff. (next semester)

 

[ June 12, 2001: Message edited by: Drax240z ]

[Kevin Shasteen]

Nother Brain-storm; it hit me (finally)-Hey, I have access to the net! Why not do a search on Cd's (I must be an out of work Rocket Scientist). Anyway, this is what I found.

 

Cd's of current cars:

1) Cd = .195 GM's EV1 Electric Car

2) Cd = .199 Ford's Prodigy (Hybrid Electric)

3) Cd = .25 Honda's Insight (Hybrid Electric)

4) Cd = .25 Lexus's LS 430 (lowest of all Sedans

5) Cd = .27 VW's Passat

6) Cd = .28 Lexus's IS 300

7) Cd = .29 C5 Corvette Coupe

8) Cd = .29 Mitsubishi Gallant

9) Cd = .29 SAAB's 9-5 Aero

10) Cd = .32 Toyota's Celica (Latest Design)

11) Cd = .33 Ferrari's 360 Modena (after 5600 hours of Wind Tunnel Testing)

12) Cd = .34 Ferrari's 355

13) Cd = .37 Ford's 94/95 Mustangs

14) Cd = .38 Dodge's Viper GTS (Down from .50)

15) Cd = .41 Ford's Late 80's/Early 90's Mustangs

 

I think the decision, on an earlier post on this thread, to go w/Cd of .31 to .34 on Mike's car was an appropriate one.

 

I had no idea till I researched it that the initial Vipers had a Cd of .50(?)! That's incredible..I remember reading about the car in early tests; I remember the driver talking about the car shaking violently as he approached top speeds....now we know why. It was hitting a brick wall of air.

 

Just for fun-lets use Mike's point about a sub 500hp Viper to see what its max mph speed should be (the Viper Site I found listed the Viper's height = 48.35 & width = 76.18 w/a Cd = .38; this gives us a frontal Area = 38.68 & lets say the Viper's peak 500hp/6000rpms attempting to hit max speed-what is its max speed?

 

V^3 = ((500 x 15 x 10^4)/(.38 x 38.68))

 

V^3 = 5102596.201

 

V = Cube Root(5102596.201

 

V = 172mph

 

Look out everyone-I've got a new toy to play with (areodynamics); too too cool!

 

That Viper site also listed the GTS Viper w/3.07 rear gears & 27.5" rear tire. This would put the above theoretical 172mph at:

 

1) 6451rpms in 5th gear

2) 3225rpms in 6th gear

 

Kevin,

(Yea,Still an Inliner)

 

PS: Mike-What I dont understand or have the knowledge to offer; is what torque is needed at high speeds to reach a 200mph objective? Have you considered your rear gear possibly being too steep for a road rally car in relation to your engine's torque/hp characteristics?

 

[ June 12, 2001: Message edited by: Kevin Shasteen ]

[Mikelly]

The reference to weight was specific to the T56 .5 gear ratio and possible trouble the stock Vipers have in running top speeds in 6th gear. Most of that was due to additional weight. Hennessey claims his Venim 800 only uses about 6# boost per turbo (Twin turbo configuration) to make his 200MPH runs in his viper kits... and his 6 speed T56 is unchanged except for the presure plate and short shifter... That tells me that the T56 is a viable candidate for the job. However, the Z has dirty CD numbers as has been discused above and that will have to be sorted, as I plan to run something different on the front end, and maybe have to change the configuration of the car to accomidate a turbo or supercharger to add power...There...I just said it... Yes, I'm thinking about adding an additional 100-200HP by gooing into the motor and lowering the compression, swapping the rotating assembly, and getting a BIG super huffer....

 

Keep the info coming guys... I'd like to hear that Ican do this without the super huffer if at all possible... to give you guys an example of how bad the CG#s are on the Z, a 3rd generation Camaro hit 185+ a few years ago with only about 450 Flywheel HP... They have much better CG numbers...

 

Mike

[DavyZ]

With a sophisticated ram-air system (like smooth sheetmetal oval tubes with no airfilter) you'd think that it would have a very strong effect at say 150mph+? Ya think?

 

I know the huffer is better, just much more costly with the engine mods you'll have to do.

 

David

[Kevin Shasteen]

Mike,

 

I was wondering about your current engine/stroke, comp, rear gears-that you're actually set up for drag racing..the comp.ratio you could live w/if the stroke were less.

 

Have you had a chance to look at the book I was talking about-it has a great explanation on how to find CG; fore/aft & from side to side...I dont know what it was called before it was re-written I only know what it is called now "Mustang Performance-Handbook 2" & by William R. Mathis.

 

By their explanation-CG seems pretty easy to find; also making one of their jigs for determining weight of the car at each wheel seems pretty easy (as resourceful as you are) I bet you could make one in a 2/3 hours; check the book out!

 

Kevin,

(Yea,Still an Inliner)

 

[ June 12, 2001: Message edited by: Kevin Shasteen ]

[BLKMGK]

One of the recent mags talked about a ram-air setup on a salt lake setup. At speed it was only making a pound or two of boost! Remember - at those speeds the engine is ingesting a ton of air. Might be interesting to instrument and see though!

[Kevin Shasteen]

Jim,

 

That very "Idea" can be determined on paper thru formulas. Both the amount Displacement air and the amount of Ram Air thru the Outer Air Intake.

 

A few Auto Math books I have talk about the very subject: I'm not an expert so I'll attempt to paraphrase it intelligently as I can.

 

I)Gas Velocity Thru Pipes/Ports

 

Example: Free Breathing 350 V8 running at WOT @ 6500rpms using a carb w/4 identical venturis, each of 1 11/16" diameter w/VE = 85%. What is the gas velocity thru each venturi? The author suggest not envisioning air as one long continuous "string" but more of a slug of air "a cylinder of air"..as this makes it easier to mentally digest.

 

The author claims theoretically every 4stroke engine inhales a volume of air equal to half its displacement w/every revolution: 1/2 of 350 = 175.

 

175 x 6500rpms x .85% = 966,875 cu.in/minute = @ 560cu.ft. (1cu.ft = 1,728 cu.in)

 

4 Venturis; each identical & handling 1/4th the total; 560/4 = 140cu.ft./min

 

Next you have to determine the cross sectional area of the venturi: 1 11/16 = 1.69

 

A = .7854(D)

 

A = .7854 x 1.69

 

A = 1.327 sq.in or @ .0092 sq.ft (where 1sq.ft. = 144sq.in)

 

Remember we're dealing w/a slug of air; we now need to determine what the size of that slug is-as we know its volume to be 140cu.ft. All we need is to know its length.

 

V of Cylinder = A x H

 

H = V/A

 

L = 140/.0092

 

L = 15,217 ft

 

So, the rate of flow is 15,217ft/min which is 253ft/sec which is about 173mph!

 

Now, the subject of Inertial Ramming's effect on engine output at high speeds (Air Intake-AKA: Hood Scoop of some design)

 

Even tho the air is still & the car is moving-its obvious (to us anyway) that one can reverse the role & envision the car standing still & the air moving-this is why the ducts on hoods face forward: this ram effect is called "Velocity Pressure" sometimes also called "Velocity Head".

 

The example given is for a vehicle at 100mph; the books reminds us that air weighs .076 lbs/cubic ft at atmospheric pressure of 14.7psi.

 

The formula is:

 

Pvel = P*V^2/4311

 

where:

 

Pvel = Velocity pressure, psi

p = air density, lb/cu.ft.

V = car velocity, mph

 

Pvel = .076*100^2/4311

 

Pvel = .18 psi

 

The book claims this "less than 1%" increase in power output is minimal due to the air's entry into the engine: which is always at right angles in direction of travel, and certain amount of energy is lost due to the needed 90* bends in the plumbing.

 

The fraction of recovery actually obtained (called the Pressure Velocity) can be as high as 97%; it can be as slight at 13% dependent upon it's angle of entry. Even w/the best design its rare that 90% is obtained.

 

It goes on to say that the Velocity Recovery is dependent upon the "square of the speed". So at a higher rate of speed-the results increase as well.

 

The next example given was a race car @ 180 mph w/Velocity Recovery of 90%. (The .9 in the formula represents the Velocity Recovery)

 

Pvel = .076*180^2*.9/4311

 

Pvel = .5 psi

 

Power Increase of about:

 

14.7 + .5/14.7 = 15.2/14.7 = 1.034 (@ 3%)

 

Power Increase = 3%; now if you've had the engine dyno'd then you'll know its torque/hp output at that rpm. You can then multiply its .3% x Torque & HP for its actual increase in power.

 

I thought it was pretty interesting!

 

Kevin

(Yea,Still an Inliner-W/a very low Velocity Recovery %)

 

[ June 13, 2001: Message edited by: Kevin Shasteen ]