Cobra Safety and HP

[searanch]

...Bish and Gary are my good neighbors and always play nice - Richard designed the best suspension system for a cobra replica and when I get some sh*t off my plate is gonna build me one - BiB is __________ you fill in the blanks

JBL - rolling art...



It has been a long and wet Washington state winter and the sun is finally out and shining in all its glory - damn its pretty here...

Oh, Ron is a really good guy too and great in a game of scrabble...

[Richard Hudgins]

Hey folks,

This has gotten way off topic.

My original point was just this:

Keep the power to weight ratio in the 8 to 10 area and all of the current chassis would be relatively safe from a dynamic standpoint.

Meaning that you would not be dealing with an inherently unstable platform due to excessive power. Now I know that folks will say that they can control their right foot. But from experience, I will have to say that they cannot. The traction equation is very complex and time based. Very few humans can keep up with 5-1 ratios. Even fewer can use them effectively.

There are very good reasons that F1 cars have traction control.

There are also very good reasons that current fighter aircraft are computer controlled. Their power to weight ratio (and control surface dynamics) are such that they cannot be flown by a human without computer assist. They are designed to be inherently unstable. They are faster this way.

F1 cars are designed using this same philosophy. But take away the computer controls and they are undriveable.

The Cobra is not computer controlled. It is controlled by the driver. Therefore, the design must allow for the human.

8-1 is the area that normal folks on the street can deal with. Note: this is not to say that they cannot deal with lower ratios, it just fits the engineering application and capabilities of the normal driver. (I know that it hurts to put yourself in the ranks of the "normal driver, but that is where 99% of us are.)

Remember, I am speaking of street cars. On the street, used everyday. Not track cars. They are a special design case in a controlled environment.

In other words. There is such a thing as too much HP.

But everyone who wants talk about building a JBL or any other Cobra chassis does not listen. They all want 500+. I try my best to get them to listen to reason.

They never do.

[Dan Semko]

Richard,
Thank you for the engineering logic. Your points are well taken.

[Bish Wheeler]

Richard,

Thank you for your thoughts. Terribly sorry that the thread got pulled of the focus. And I really do agree that there is such a thing as too much HP

Bish

[Neal Jackson]

Richard,

Man, I'm glad you didn't include Cheetahs!! I may have to rethink what I've done!

[Bill Kesner]

Neal,

How is that beast of yours coming along? I was spreading a rumor that you were putting Shelby's new CSX Aluminum big block into your car. I can't even imagine the steering wheel staying on after you step on the throttle.

- Bill -

[Excaliber]

Neal,
Oh I'm sure Richard wasn't talking about Cheetahs. No sirree!

Ha ha!

Ernie

[Neal Jackson]

Bill,

Well, it rolls, drive train is in, steering is being hooked up, as are the shocks and about a million other little detail items.

Nope, can't afford no alum BB Shelby 427 - had to stick with an Eldorado 500 Caddy mill.

Ernie,

Yes, and I am relieved he wasn't. Not sure of the power to weight ratio, but the cube to weight ratio is in the 3.6 range.

[Excaliber]

Ha ha,,,cube to weight ratio??? Now theres a twist, you might be onto something.

Ernie

[750hp]

Richard - I value your input and have benefitted from your experience when I needed advice on various suspension, differential and braking components. I know that you speak from not only an engineering background, but also from a history of track time in such high powered vehicles that includes.....

Originally posted by Richard Hudgins
Examples of cars that I have driven with spools.

1. Porsche 935 2250 lbs. 89.75 wheelbase, 500>750 hp. (depending on where you set the boost.) A pure joy to drive once you got onto the power delivery issues.

2. McLaren M8 . 1750 lbs. 92 wheelbase 700+ hp. Really a cool car to drive and the motor was excellent in power delivery.

3. Lola T300 1550 lbs. 94 Wheelbase, 550 hp. Ok to drive but the chassis was really flexible and you had to be careful not to have the bodywork and chassis pinch you under the arm due to flex.

As you may have read, I have built exactly the type of car that you have questioned the logic of, and reasoning behind. I cannot think of one good reason of why I need this level of power. In fact, I felt pretty queasy when I realised what I had gotten myself into. You see, I had planned on building a lightweight 400hp carburetted road/race Cobra originally. By the time I had placed my order for the engine, the entire reason for building a new Cobra was already out the window. With the new level of power came all sorts of other problems - such as now requiring high strength "drag-racing" style driveline components in place of the light-weight roadracing parts that I had planned to use.

All that being said, I've now spent my money and have ended up with what I think is a fairly unique car that screams performance. I still value the driving experience that comes with owning one of these cars, and I don't just want to park my car in a garage with the knowledge that I have one of the more powerful Cobras around. I still want to drive and enjoy my car.

Realising my limitations, and knowing that my level of power is drastic overkill for the street, I have had OZVENOM install some GT101 Hall Effect sensors from and rear as wheel speed sensors for the purposes of traction control (via my Motec M800). As you would be aware, the percentage of wheel slip can be dialled in to suit the vehicle. After that long winded insight into how I ended up where I am, I have a genuine question for you. How would you expect a Cobra chassis to cope with an 800hp motor if the traction control was dialled in to allow no more than 5 or 10% wheel slip. If the traction equation was levelled by the sophisticated traction control software, do you think that more than 400hp can be used on the street?

Would the problem with "too much power" then become more of a driver attitude/ego problem, rather than a chassis dynamics problem? To be honest, I cannot see a need for ANY Cobra to be accelerating at full throttle for more than a couple of seconds on the street. After seeing the datalogging of my car on the racetrack last Wednesday, I'm quite convinced that I'll NEVER need to use full throttle on the street. Thanks for taking the time to read my lengthy post. I hope you see this as a legitimate question, rather than a poor attempt at trying to justify my car.

Craig

[PatBuckley]

Wow!

Richard, did you actually RACE those cars?

I am impressed!

Pat

[Richard Hudgins]

Craig,

You are a special case. I doubt that there would ever be TOO MUCH HP for you. It is an OZ thing as you know.

However, to you question.

By installing traction control, you have in essence controlled (read reduced) the HP (or Torque) that the chassis will see in a dynamic situation. Exactly the correct thing to do with your engine/chassis combination. By using traction control you have taken an inherently unstable platform and applied controls that will allow this platform to remain in a stable longitudinal dynamic window.

Percentage of slip is a complex issue. 5>10% is a good starting point. CART cars run as much as 30% and as little as 2% depending on venue and track conditions. The slip is adjustable from the cockpit in order that the driver can change for slow speed corners (More slip) and high speed corners (less slip).

One thing to remember, single dynamic traction control is not a panacea for total traction. Remember the friction circle. There is X amount of adhesion available from the contact patch. Applied lateral traction will diminish the amount of longitudinal traction available and vice versa. In other words, if you have the tires loaded laterally at 98% and you step on the throttle you will only have a 2% slippage allowance longitudinally. (In essence a 5% slip setting has now put you in the boonies.)

Traction control in F1 and CART cars also use multiple yaw sensors to factor in these variables. They also use fly by wire throttles and throttle position is altered to affect traction control and remain within the friction circle. You will notice that they still put them off now and again even with the best of systems. (Launch control is a whole different beast.)

However, you are going the right direction. With the Motec M800 I think that you are limited on the digital input side to 4 inputs for wheel sensors. I do not know if they can read the A>D outputs of two accelerometers and correlate with the wheel speed sensors to provide total traction control. But I am sure that OZVENOM will know how to do this and program them correctly. But with a manual throttle I do not know if a really effective friction circle system can be developed. But you can certainly make a single dynamic system work well.

You will need it with that monster motor. (I know that I would.)

[Bart Carter]

Originally posted by Richard Hudgins Keep the power to weight ratio in the 8 to 10 area and all of the current chassis would be relatively safe from a dynamic standpoint.

Meaning that you would not be dealing with an inherently unstable platform due to excessive power. Now I know that folks will say that they can control their right foot. But from experience, I will have to say that they cannot

OK, maybe I am looking at this from a different point of view. If you have a HP curve that gives you 300 HP at 3500 RPM and 500 HP at 6500 RPM, anyone should be able to shift at 3500 RPM. It doesn't take that much skill.

If it is a problem, set the rev limiter to 3500 RPM for your street driving.

When you track your car, reset the rev limiter or shift where appropriate.

My 2 cents.

[Jahred]

Richard, thanks for posting. Given your background your comments are well worth reading.

I make a point of reading all such commentary, cause these cars are dangerous. Not sure I agree altogether on the driveability issue. I have a 514 crate, with a performer type manifold and while I don't sit at stoplights much, I certainly have no difficulty driving it around town. It is quite friendly all around.

I have never floored it in first or second. Not sure I ever will. Great traction, though I am sure there are plenty of guys out there that could run circles around me at the track in a small block.

But most replicas are 427SC. That is really what made these little bugger's famous. That really is what we marvel about. THEY ARE EXTREME. So it seems to me your comments are a bit unrealistic. A 427SC replica should have over 300HP. I think the compression on mine is 9.8:1. Pump gas, pretty friendly.

And you can't help but shake your head any time you look at it............but that is why I built it. GodSpeed to all and do be carefull.

[BANDIT 1]

I enjoy having a 505 horsepower Viper pull up next to me and "punch it" for 2 - 3 car lengths to show me his cars acceleration. I enjoy taking the Cobra and doing the same thing. Once the other driver see's the acceleration of the Big Block Cobra, the so-called "street race" is over.

You all have been watching too much T.V. and movies and you assume every so-called "street race" is like they show it in "The Fast And Furious" where two cars are maxed out for several miles, get real.

I guess none of you "preacher types" have never went above the speed limit ever, not even because you were late to work or something.

If you all want the Cobra to be the perfect "road race" car, I suggest a 6 cylinder engine.

[casaleenie]

Originally posted by G.R.

Because I've wanted one since 1966 and can now actually have one. [/b]

G.R.,

The same for me..... I saw my first one in 1964 and wanted one..
It was a thing of beauty just sitting there.. The fact that it is fast and powerful is a plus but not the main reason for wanting and buying the car... I smile just looking at it... the rest is pure gravy.

[PatBuckley]

"Wow!

Richard, did you actually RACE those cars?

I am impressed!

Pat"



Richard -

I am serious - did you?

Pat

[Excaliber]

Ha Ha,,,,,,well it's obvious you got your work cut out for you Richard. I see what you mean about encouraging new buyers to keep a limit on the horse power, and they don't usually listen. Might have something to do with the type-A thing.......

Ernie

[Bill E]

----quote----------------------------------------------------------------------------The bottom line is quite simple. You design vehicle systems for the application and the end user capabilities. ------------------------------------------------------------------------------------------------------------ Right on!!!!!!! Richard I would be honored to have you go over one of our cars any time. We are now offering Traction control to any one over 375 FP of torque Even The best of drivers can have a laps of judgment. And whit it turned way up in cut our mode they don't tend to crash them the first time out.lol

[Excaliber]

Hey Bill, how about a few details on the trac control system?

Brakes, throttle response, engine timing, what? How is "wheel slip" determined? Who manufacturs the system? Cockpit adjustable? Cost? Adaptable to "other" Cobras?

Ernie