Kirkham Question

[fastd]

I've been to the Kirkham website but answer to the following question is not apparent (to me anyway)

Kirkham does the most accurate Cobra reproduction, right? So what does the frames on Kirkham's look like? Are they the original ladder frame famous for flex and twist, or does Kirkham offer their own design? As well as the original design? How they keep the weight down? And then there's the other makers like Backdraft and Factory Five that I think both weigh in the low 2000s...

I have an ERA and have been told that the reason they weigh 2500-2600 bps is because 200-300 lbs is due to the beefier frame.

And, since I'm at it, what does the weight/frame strength mean in terms of performance - lateral g's and overall handling - anybody driven more than their own manufacturer that can share their experiences?

[RodKnock]

Most accurate reproduction? In terms of the "mass-produced" replicas, yes. Shelby uses them for their replicas. I'm sure there are some boutique-type shops around the world, someone maybe like Mike McCluskey in SoCal, or Hall Fabrication in NorCal, or in England somewhere, that could probably scratch-build one more accurately for alot more money and time.

Kirkham keeps the weight down with billet aluminum suspension and brake parts and an aluminum differential, halfshafts, CV joints, etc.

[Dimis]

I'm not sure I'm edumacated well enough to answer all your questions but I can share these pics of Kirkham's Stainless steel chassis.














Yes they are Ladder frame, birdcage frames, as you can see in the pics, however I believe they use a thicker gauge of steel for chassis rails, etc, so aren't as flexy as originals.

Kirkham does offer a billet chassis, most probably stiffer than anything, but that costs more than most could afford.





They keep the weight down by using Aluminium throughout the car, as opposed to fiberglass, or steel (ie: suspension pieces, or door, hood, truck frames, etc).

I cant advise on Backdraft or Factory 5, but ERA chassis is built differently, using square tube and not round tube, some extra bracing, to make their frame stiff, but the small compromise is weight. In my experience, Stiffness is more important that weight.

The theory would suggest less weight would be faster, but if it aint suitably stiff, then it wont be able to get the traction required to pull the lateral Gs

[rodneym]

More than likely a Kirkham or original style chassis is P-L-E-N-T-Y stiff for us mere mortals. Consider what the originals did, or even CSX3170 and his recent autox successes.

Besides, IMO it would be tough to quantify how much better performing a "600 LB stiffer" frame would react unless you A/B'd them with the same motor, driver, etc. Like I said in another thread...until it's been done, it's all bench racing and fairy tales. Personally, I'd rather have a 2100 LB accurate chassis Cobra than a 2600 LB stiffer one. And as far as where the added weight comes from, it's more in the glass probably. A glass CSX is in the 2500-2600 LB area, no?

For what it's worth, I remember sticking the tips of my fingers between the door and cowl of my old SPF while driving. Judging by the amount of pinching I felt compared to the same "test" with my Kirkham, I'd say the Kirkham is quite a bit stiffer (much less movement). I know, it's not scientific

That's no dig to SPF. They're fantastic cars.

[DanEC]

If I remember correctly the main 4 inch frame tubes in the standard Kirkham chassis are slightly thicker steel than the original chassis rails, so from that alone, they would be stiffer than originals at a slight penalty in weight. I think a thick fiberglass body such as ERA uses is a little heavier than a Kirkham body also.

[MOTORHEAD]

Plus the ERA body is bonded to the frame, providing some additional stiffness.
But now that I think of it, the Kirkham (and Shelbys) aluminum panels are riveted to the birdcage part of the frame, so that should help some in the rigidity department.

[Mark IV]

Originally Posted by fastd

I've been to the Kirkham website but answer to the following question is not apparent (to me anyway)

Kirkham does the most accurate Cobra reproduction, right? So what does the frames on Kirkham's look like? Are they the original ladder frame famous for flex and twist, or does Kirkham offer their own design? As well as the original design? How they keep the weight down? And then there's the other makers like Backdraft and Factory Five that I think both weigh in the low 2000s...

I have an ERA and have been told that the reason they weigh 2500-2600 bps is because 200-300 lbs is due to the beefier frame.

And, since I'm at it, what does the weight/frame strength mean in terms of performance - lateral g's and overall handling - anybody driven more than their own manufacturer that can share their experiences?

Important point: Are you talking Mk II ("289") or Mk III ("427") chassis?

[fastd]

Originally Posted by Mark IV

Important point: Are you talking Mk II ("289") or Mk III ("427") chassis?

What's the difference?

[Dimis]

Originally Posted by fastd

What's the difference?

Leaf springs for a start.




While not Kirkham, this scratch build will give you an idea:
Fox' 289 Leaf Spring Chassis




I've just assumed you were chasing info for a "427"...

[MOTORHEAD]

"260/289" chassis 3" tube rails
"427" chassis 4" round tube rails, & I think I read somwhere 4" more distance between rails, and chassis and suspension designed by Ford engineers on Fords first computer.
All done to accommodate the FE big block.
The "small" Cobra chassis may have been antiquated, but it still won more than it's share of races!!