The 427 Cobra that AC Cars was SUPPPOSED to build

[RunWithScizzors]

Here's a question for the historians out there.
I'm reading in Trevor Legate's book Cobra, The First 40 Years (pg 132) that when it came time to design the 'Mark II' Cobra, the engineers specified a 3" longer wheelbase. But... "When Negstad arrived at Thames Ditton he found that AC had already taken delivery of the main frame tubing, cut the same length as the original, since they found they could get a better price on that size and quantity."
Also, that the lightweight 390 CID engine was originally selected, but Ford's NASCAR customers wanted exclusive use of it. Ford made the 427 SO available instead, throwing his weight distribution calculations out the window.
(One wonders what ELSE was different.)

Q: Have Klaus Arning and Bob Negstad's original engineering drawings survived?

[cycleguy55]

That would have to be the Mark III Cobra - the Mark II was still a leaf spring chassis, albeit with rack and pinion steering.

[eschaider]

Originally Posted by RunWithScizzors

... Q: Have Klaus Arning and Bob Negstad's original engineering drawings survived?

They have and are findable and down-loadable off the internet.


Ed

[RunWithScizzors]

Originally Posted by cycleguy55

That would have to be the Mark III Cobra - the Mark II was still a leaf spring chassis, albeit with rack and pinion steering.

Just quoting the author. Legate (still pg 132): "Known within AC Cars and Shelby American as the MkII Cobra..."

[RunWithScizzors]

Originally Posted by eschaider

They have and are findable and down-loadable off the internet.

Thanks! They would be fascinating! I see elsewhere a lead to Cobra Restorers, which I'm checking out.

[blykins]

The 390 wouldn't have been lighter weight. All FE blocks are the same. If anything, the 427 is lighter because the bores are larger.

I think a lot of the stuff you read is speculation or opinion.

[Mark IV]

I had the privilege of knowing Bob Negstad and had a couple of interesting conversations with him. When I met him he was with SVO and had designed a bolt-in IRS system for the proposed SVO Thunderbird Turbo Coupe. My introduction to Bob was with Brian Angliss of Autokraft.

Bob had an AC MK IV a little later as well as Mike Kranefuss head of SVO with engines built by Jack Roush (way before his crate engines) Bob told me if he, Mike and Jack all dropped the clutch on their MK IVs at the same time, the Earth's rotation would change!

Bob had a Fairmont boxtop that was full SVO underneath with a lot of trick pieces from Ford suppliers. Looked like Grandma's car and went like stink and handled fantastic.

[RunWithScizzors]

Originally Posted by blykins

The 390 wouldn't have been lighter weight. All FE blocks are the same. If anything, the 427 is lighter because the bores are larger.

I think a lot of the stuff you read is speculation or opinion.

Perhaps Legate was referring to the aluminum 390 that Ken Miles ran in CSX2196 at Nassau in 1964. It would certainly have been lighter than the iron block FEs. But I don't know if that's what the weight distribution calculations were based on - just speculating here.

[cycleguy55]

Originally Posted by RunWithScizzors

Just quoting the author. Legate (still pg 132): "Known within AC Cars and Shelby American as the MkII Cobra..."

I appreciate that - I'm not attempting to 'shoot the messenger'.

There's a great deal of lore, myth and misconception surrounding Shelby and his cars over the years, and even well-respected authors haven't always gotten the details correct. Regardless, apparently the SAAC registry (p. 1598) indicates MkI Cobras are the worm-and-sector cars and MkIIs are the rack-and-pinion cars.

1965 289 Shelby Cobra - Mark II or Mark III?

https://en.wikipedia.org/wiki/AC_Cobra

[RunWithScizzors]

We're good, Brian. Thanks.
The "Mark" designations seem to have drifted over time. In your linked post, A-Snake says "However, in period the reference was different. There wasn't a MKI until there was something to replace it. The coil spring car was called the MKII leaving anything produced prior known as a MkI. I know, a little confusing."
Also, none other than Peter Brock uses "Mark II" here: https://classicmotorsports.com/artic...-raced-part-2/ (and corroborated Legate's story of the specified 93" wheelbase)
All part of the fun!
Whatever we call them, I'm still looking for Negstad's original engineering drawings specifying a 93" wheelbase. Does anyone out there have a link to a download?

[LMH]

Mark I and Mark II came into usage shortly after production of the Cobra ceased. The story as I heard it was that an employee of AC Cars used the designation while trying to get the correct replacement parts to a customer. He made it up on the fly sort of thing. The terms weren't applied to cars during production period. The Cobra 427 was originally called the "Cobra II" but Shelby didn't like the term.
Larry

[Dan Case]

Originally Posted by LMH

Mark I and Mark II came into usage shortly after production of the Cobra ceased. The story as I heard it was that an employee of AC Cars used the designation while trying to get the correct replacement parts to a customer. He made it up on the fly sort of thing. The terms weren't applied to cars during production period. The Cobra 427 was originally called the "Cobra II" but Shelby didn't like the term.
Larry

The parts department at Shelby American had their own naming conventions.

The January 15, 1965 Shelby American parts book there were “COBRA I” and “COBRA II” vehicles. It was very important to tell the parts department what your chassis number was so they knew which parts your car would require. (The race wheels Halibrand created for 427 Cobra as marked “COBRA II” I believe.


The December 23, 1966 Shelby American parts book there were “Model 1…1963-65” Cobras and “Model 2 in the Cobra series indicates the Cobra 427…”.

The earliest "MK" anything I have located was in correspondence between the AC Cars parts department and the owner of a COX61xx chassis trying to get information in 1972. Months of confusing correspondence included "MK" naming in the June 26, 1972 letter to the owner. AC was giving answers specific for a leaf spring chassis suspension set up until that letter.


Over time all kinds of MK (Mark) definitions have been created. I have no idea who started the "Mark" naming, could have been just about anybody at any time a change was made. I have read everything I could get since the 1970s. Owners and fans seem to disagree more than agree. When new drawings were done in November 1962 for what became the CSX2126-CSX2164 chassis version the title was "DESCRIPTION:- CHASSIS FRAME" for "MODEL:- 3•6 ACE". Some I have seen include:

MKI = all leaf spring cars no matter which engine or steering system, OR leaf spring cars powered by a 260 engine no matter what the chassis number was, OR a leaf spring car with the cam and follower based steering system no matter what engine was installed. (June 26, 1972 AC Cars letter “…COBRA Mark 1.” chassis had transverse leaf springs with “…an earlier type of front suspension.”.)

MKII = leaf spring chassis with a 289 engine installed no matter what the chassis number was, OR a leaf spring car with rack and pinion steering, or a coil spring chassis with 427 or 428 engine. (June 26, 1972 AC Cars letter, “…COBRA Mark 2. has transverse springing...”)

Note: The prototype Cobra started off with a 221 engine. There were leaf spring cars outfitted with 260 engines and 289 engines. There were chassis outfitted with cam and follower based steering that had 260 and 289 engines. CSX2196, a leaf spring car with rack and pinion steering, first received a 1964 Galaxie R Code 427 8V engine. CS 2030 was the prototype car for rack and pinion steering. Most of the MKI and MKII names definitions get blown up real quick, except the two in the AC Cars letter.

MKIII = usually means coil spring chassis with either a 427 or 428 engine BUT some call it a coil spring chassis with a 289 engine (AC Cars 289 Sports). (The June 26, 1972 letter to an owner of a COX61xx chassis was told, “…it is definitely called a COBRA Mark 3. Coil suspension.”, which is the very first factory reference sentence I have come across using “Mark” anything.)

None of these really help original car owners much if any. Since the day they were sold getting the correct parts for any original car meant having the chassis number ready for the parts and service departments. There were chassis orders and then within those orders specification changes were made. Was your car a street car or factory prepared race car? Two chassis one number apart can be very different. For example, two production specification change sets most may recognize include the change in steering system at CSX2126 and the change in electrical systems at CSX2201. Literally hundreds of parts or subsystems changed between CSX2001 and the last 289 Sports.

[eschaider]

Originally Posted by RunWithScizzors

...
Whatever we call them, I'm still looking for Negstad's original engineering drawings specifying a 93" wheelbase. Does anyone out there have a link to a download?

I had a set of the original IRS drawings in the early 2000's that was missing one page which was possible to create from the others, but they are not where I thought I saved them. Even worse, my searches are telling me they are no longer on my hard drive. I don't recall, although that doesn't mean there was nothing there, commentary about a 93 inch wheelbase design.

My own internet searches this evening did not find the drawings I had found 20 years ago. That said, the design was patented by Ford and was sought after by Chrysler, I think AMC and BMW or Mercedes.

I believe the best source for the significant portion of the design today, is probably the US Patent and Trademark office. The original patents detailed and described in words and drawings the special attributes of the design necessary to get the patent.

My notes indicate the patent number was US3189118 and I want to say it was filed in February or March of 1961 if that helps. I think there may have been revisions and refillings to cover the revisions. The original patent number should put you on the trail however.



Ed

[RunWithScizzors]

Ed, thanks for your efforts!
I wondered at the top what else might be different. Brock's article tells us "Negstad was livid, but there was little he could do. He had to hurriedly redesign his rear suspension with shorter lower links. This compromise skewed the toe curves on his perfect design, and he was never happy with it."
The fun continues...

[cycleguy55]

Originally Posted by eschaider

I had a set of the original IRS drawings in the early 2000's that was missing one page which was possible to create from the others, but they are not where I thought I saved them. Even worse, my searches are telling me they are no longer on my hard drive. I don't recall, although that doesn't mean there was nothing there, commentary about a 93 inch wheelbase design.

My own internet searches this evening did not find the drawings I had found 20 years ago. That said, the design was patented by Ford and was sought after by Chrysler, I think AMC and BMW or Mercedes.

I believe the best source for the significant portion of the design today, is probably the US Patent and Trademark office. The original patents detailed and described in words and drawings the special attributes of the design necessary to get the patent.

My notes indicate the patent number was US3189118 and I want to say it was filed in February or March of 1961 if that helps. I think there may have been revisions and refillings to cover the revisions. The original patent number should put you on the trail however.



Ed

Here's a link to US3189118A:
https://patents.google.com/patent/US3189118A/en

Download PDF (23 pages): https://patentimages.storage.googlea.../US3189118.pdf

Of note is this patent is cited by 30 other patents.

[eschaider]

Thanks for digging it up Brian. I should have finished the job, glad you did.


Ed

[RunWithScizzors]

Once again, you guys never cease to amaze!

[MKS427]

[quote=blykins;1491968]The 390 wouldn't have been lighter weight. All FE blocks are the same. If anything, the 427 is lighter because the bores are larger.

The 390 in question was an experimental all-aluminum FE engine. The engine would not hold up earning Ken Miles' car the nickname The Turd.
Ford wanted to showcase the FEs. However, the drivers wanted lighter cars with stroked small blocks. Ford brass won.

[Trevor Legate]

Nice to see the old 'Mk' discussion still rumbles on..and on.... and... Speaking as one wot done lives on the right-hand side of the Atlantic divide I can confirm that back in the mid Sixties (I was there...) the question of MkII or III didn't exist. The 260/289 Cobras were known over here as AC Cobras while the 427 was a Shelby Cobra as it was not available in the UK, so twas not an AC.
The technical drawings produced at AC for the 427 show it as the MkII - which it was. Thus today, within the Hallowed Halls of the AC Owners Club, the 427 shall be for evermore the 'MkII'. However, in the outside world, the 'II' and 'III' designation has become part of Cobra culture and everyone knows to what it refers. Fine by me....
My 2 cents.

[Mark IV]

Originally Posted by Trevor Legate

Nice to see the old 'Mk' discussion still rumbles on..and on.... and... Speaking as one wot done lives on the right-hand side of the Atlantic divide I can confirm that back in the mid Sixties (I was there...) the question of MkII or III didn't exist. The 260/289 Cobras were known over here as AC Cobras while the 427 was a Shelby Cobra as it was not available in the UK, so twas not an AC.
The technical drawings produced at AC for the 427 show it as the MkII - which it was. Thus today, within the Hallowed Halls of the AC Owners Club, the 427 shall be for evermore the 'MkII'. However, in the outside world, the 'II' and 'III' designation has become part of Cobra culture and everyone knows to what it refers. Fine by me....
My 2 cents.

Trevor,

So you have finally crawled out from under the rock you have been hiding under? Been a while.....