Million Dollar Skunksworks Kirkham

[Don]

David, should you desire to publicize the accomplishment, via an interview and article, consider MotorSport, i.e. international recognition and exposure

http://www.motorsportmagazine.co.uk/

Simon Taylor writes terrific articles. He interviewed NicK Mason, drummer for Pink Floyd, on the CD " The Sounds of Goodwood " For those that are not familiar with MotorSport, a very high quality publication, a natural for the vehicle being constructed.

[David Kirkham]

Originally Posted by lineslinger

My comments were not meant as a suck up, craftsmanship is always to be noted, if your customer starts to pick it apart I would like to discuss the project with you..no BS.

My customer has really been one of the nicest men I have ever dealt with--maybe even the nicest. He has never nit-picked anything I have done. On the contrary, he has been quite complimentary...the funny thing is, the more complimentary he is, the more I want to make the car even better just so there is no possibility I could let him down. I am just nervous, that's all; I really don't even know why, I just am.

David

[David Kirkham]

This is a really interesting part. This is the pedal box. On the original 427 Cobra, the master cylinders for the brakes and clutch is under the floor. My customer told me one day he wanted to drive this car down the PCH from San Francisco to LA. One of the problems with the original car is you can't slide your foot under the brake pedals because they are floor mounted. We thought a lot about this and decided to hang the pedals from the top.

The problem is; if you hang the pedals from the top, they are right above the exhaust and they will "pre-heat" your brake fluid for you! Bad, very bad--especially if you are facing turn 1 at the end of the straight and you already have your brakes hot. So, we flipped the master cylinders around so they face the driver and the brake pedal turns into a class 1 lever (just like a teeter totter). It made things tight, but it was the only answer that worked.

[David Kirkham]

Notice in the above box we made 2 internal supports for the pivot pin. The stiffness of the pedal box is critical to brake feel. You do NOT want your brake pedal or pedal box flexing! You do not want anything in the brake department flexing as it gives the driver a vague feel of what the brakes are doing. Flex makes modulation of the brakes impossible (or at least very difficult). So, we placed intermediate braces in the box--between the brake and clutch pedal levers--to mitigate any flex that could creep into the system. Also, the front of the foot box is made from 1/2 inch aluminum plate. The top of the foot box is made from 1 inch plate! (All hogged out and lightened up, of course.)

[David Kirkham]

Here are the brake and clutch pedals.

You can see we designed them so there is clearance for your toe as you work the pedal. We designed the pedals straight so there would be no chance of the pedal flexing under hard braking. The original Cobra brake and clutch pedals are bent to put them in the right place for the driver to use them. The bend in the pedals is weak spot that causes the pedals to flex. That was a problem we had to solve in this car.

So, we placed the pedals optimally in the foot box for the driver, but that caused problems lining up the pedals with the master cylinders as the pedals are nowhere near directly under the master cylinders. So, we machined the offset into the top of the pedal--along the axis of the pivot pin--thereby eliminating any side loading of the pedals or the master cylinders.

The down side is the billet to make the pedals was 4 x 2 x 20! That is 16 pounds of billet! The finished machined pedals are just over 1 pound each.

We have been asked many times how much of the billet goes into chips. I would guess on average 90-95% of the aluminum billet goes into the chip barrel. Aluminum does recycle, however!

[David Kirkham]

Oh yes, in the above picture, the brake pedal is on the right; the clutch pedal is on the left.

[David Kirkham]

This is a close up of the top of the brake pedal. This is where the brake bias bar attaches to the brake pedal. The hollow cylinder holds the bias bar bearing. When we put the bias bar in the car, I will take a pic. As you can see in the picture, the bias bar itself is also supported on the pivot pin to absolutely minimize any flex in the system.

[lineslinger]

Originally Posted by David Kirkham

My customer has really been one of the nicest men I have ever dealt with--maybe even the nicest. He has never nit-picked anything I have done. On the contrary, he has been quite complimentary...the funny thing is, the more complimentary he is, the more I want to make the car even better just so there is no possibility I could let him down. I am just nervous, that's all; I really don't even know why, I just am.

David

Keep the slide show active, I enjoy the visuals............

[David Kirkham]

This leads me to a discussion of the brake bias bar. It is very common in hot rods and even in our own Kit Car and Replica industry to see people place chokes on the rear brake line to control the brake bias. This is a very bad idea--especially in our cars that generally lack power brakes.

You see, you only have so much brake line pressure that is available in the system. If you limit the pressure to the rear brakes to get them to not lock up before the front brakes, then you are eliminating some brake line pressure that could effectively be used on the front brakes.

It is far better to mechanically bias the brakes toward the front of the car so you are then mechanically applying more pressure to the fronts than to the rears. Unfortunately, the original 427 and 289 Cobras did not have a way to adjust the brake bias mechanically. They had to do it by changing the master cylinder sizes front to rear.

In our dropped foot box cars, (where we designed the pedal box ourselves) we do run this type of a bias bar. When we do that, we actually put the largest size piston calipers available on the rear calipers so we can get the highest pressure possible on the rear caliper pistons. We then mechanically bias the brakes to the front so we can get even higher line pressure to them. That way, for a given pedal pressure, we get a higher line pressure--and hence, easier stopping of the car for the driver.

This will all become a lot clearer when I post a pic of the bias bar assembly.

Any questions are most welcome.

David

[David Kirkham]

Originally Posted by lineslinger

Keep the slide show active, I enjoy the visuals............

My fingers are hurting from all the posting and emailing I have done today. I will definitely post more tomorrow. Maybe after I play a few Chopin Nocturnes my fingers will limber up and then I will post a few more pics. But thanks for the interest! I am glad you like it. I hope others like it too and I don't think I am being a big mouth by monopolizing the CC band width.

David

[David Kirkham]

What the hey, I'll post another one.

This is a pic of the belly pan. This is the real secret why the chassis is 300% (at least that is what the FEA says) than an original chassis. The belly pan ties the entire chassis together on the under side. Also, it is the area that is the furthest from the neutral axis of the chassis. As many of you know, the farther you can move the mass from the neutral axis, the stiffer the part will be.

The belly pan was cut out on our water jet from 1/8 inch aluminum plate. It also has the added benefit of cleaning up the under carriage air so the car is more aerodynamic--although I don't think that is a major concern with this car.

[lineslinger]

Good thing you have a good piano. I use my guitar.

[David Kirkham]

Oh yes, the cut out on the top is to clear the bell housing. The belly pan runs from the engine all the way to the differential. The weakest part of any Cobra type chassis (open car) is the area of the cockpit. The low cut out for the doors makes the chassis flex in the door area. That is why many old Cobras that you look at have cracks under the doors. The original frame rails were pathetically thin and flimsy.

Now I will go and play Chopin's Nocturne Opus 27.2. I hope Chopin doesn't roll over in his grave.

David

[saltytri]

Originally Posted by David Kirkham

I hope others like it too and I don't think I am being a big mouth by monopolizing the CC band width.

You've got to be joking, pal! Since you launched this extravaganza of a thread, it's the first thing I go to when I sit down at the computer. Just keep it coming, please.

[David Kirkham]

I do have a nice piano, but one day I would like to get a European piano like a Steingraeber, Fazioli or a Bosendorfer. But with the Euro exchange rate like it is I don't think I will ever be able to justify it!

David

[David Kirkham]

Originally Posted by saltytri

You've got to be joking, pal! Since you launched this extravaganza of a thread, it's the first thing I go to when I sit down at the computer. Just keep it coming, please.

Ok, one more.

[David Kirkham]

Here you can see we got the engine firewall installed in the car. If you look closely you can see some of the zillion bolts going into the chassis.

[David Kirkham]

I don't want to even know how many bolts there are in this car! We decide to bolt the sheet metal down (instead of riveting it) in case there is a problem on the test drive. You just never know if you have to take something back apart again!

[David Kirkham]

This is a shot of the driver's foot box. We ran the bracing tube directly on top of the foot box. I was very happy (and a little surprised) the CAD was so accurate. We will screw this tube to the foot box to help prevent the dreaded COWL SHAKE.

[David Kirkham]

In the above photo, you can see the 3 holes in the top of the box for the throttle, brake, and clutch pedals. Also, you can see the steering column tube in this shot as well.

David