The BritishV8 Pub

Hi everyone, I have a question that I've wanted to ask the forum experts for quite awhile now, so here it is; Is it possible to build an MGB roadster that could compete and out perform a "Factory Five" Cobra given the same 5.0 Liter (Ford) engine?

From the Factory Five website:

Quote:

Mk3 Roadster Vehicle Specifications
Engine
Configuration Dual Overhead Cam 32V V-8 aluminum block and heads
Displacement 281 CID / 46-6 cc
Bore and Stroke 3.55x3.54 in.
Compression ratio 10.1:1
Induction Multi-port Fuel injection
Maximum Horsepower 305 @ 6000 rpm
Maximum Torque 320 @ 4250 rpm
Redline 6800 rpm

Drivetrain
Transmission 5 speed manual
Final drive ratio 3.55:1 limited slip
Clutch 10.5 inch single disc

Suspension
Front suspension type Independent double arm
Rear suspension type Soild Rear Axle 3 link with Panhard Bar
Shock-Springs Bilstein coil over with ride height adjustment
Steering Power assisted rack and pinion 2.6 turns lock-lock
Brakes Vented 13/11.65 disc f/r Power assisted ABS
Wheels 18x9 Ford Racing Cast aluminum

Tires
Kumho Ecsta MX 245/40/18 F 275/35/18 R

Vehicle
Weight 2460 lbs.
Weight Distribution F/R 46.9/53.1 (%)
Wheelbase 90 in.
Overall length 158 in.
Front Track 58.5 in.
Rear Track 58.5 in.
Overall height 48.0 in.
Overall width 70.5 in.
Ground clearance 4.5 in.

Fuel Capacity
15 Gallons

Construction
Layout Front/mid engine RWD Roadster
Frame Tubular space frame with integral backbone
Roll cage 3 point, structurally mounted 2 in. DOM Tubing
Sub-structure Aluminum paneling riveted and bonded to frame
Restraint System 4 point Simpson Harrness

Just from the specs, we can see that an MGB V8 should have two fundamental advantages and two fundamental disadvantages.

As you can see above, at 2460 pounds, the Factory Five "Cobra" can't possibly be called lightweight. Depending on how you build it, an MGB V8 roadster could easily weigh several hundred pounds less... (My MGB GT V8 weighs 2180, wet.) Assuming both cars can hook-up and that they're similarly geared, your MGB should be quicker accelerating in a straight line.

The MGB has both a lower coefficient of drag plus a significantly smaller frontal area, so it should have a higher top speed. The wildcard here is that the MGB tends to become unstable at real high speeds. I don't know how if the Cobra body creates more or less "lift" than an MGB body.

For cornering, the Factory Five Cobra's big advantage is its wide track: 58.5" vs ~49" (stock MGB). However, we have to presume that you're going to put wider tires on your MGB than stock... and when you do you can space them out some. Wider track will equate to "pulling more lateral G's" and thus to carrying more speed through corners.

See the Cobra's tire size? 245/40/18? That's a whole lot of rubber! I'll count it as an advantage in terms of handling because generally more sticky rubber will let a car corner harder. (Don't put too much emphasis on this though... I'm actually skeptical a Cobra "needs" tires quite that big. Smaller wheels and tires would weigh less, would have less flywheel effect, would cause less aerodynamic drag, etc. - I think the real reason the Cobra has such big tires is for looks. If you could really test it, you might find out that an MGB with fender flares can wear "big enough" tires to completely eliminate this Cobra "advantage".)

There are many other factors that go into "competitiveness" that are hard to evaluate from a spec sheet (for example: rigidity of the chassis, suspension geometry, etc.)

Thanks, for the very nicely composed answer Curtis.

I agree that the wide track gives the Cobra a legitimate advantage, however, you are also right to say that too big of a tire can complicate suspension and brakes. One response to fight this advantage is that Fast Cars Inc. (Ted Lathrop) now offers his front end in a wider version. The unsprung weight and steering geometry seem to be much superior to the Factory Five Cobra.

Although I've already purchased Fast Cars first version (wider wasn’t available at the time), I hear feedback from owners that the modification gives some serious improvements over the original; I'll only be able to verify these claims for myself when the car is finished and on the road. As far as tire seize/grip goes, my opinion is that the perfect tire seize for an MG with flares should be P215-50ZR16 in front and P225-45ZR16 in the rear. It takes quite a bit of work to accommodate this set up.

I also agree about the MG’s aerodynamics being a plus, however, I believe that a front spoiler should be installed on any light weight cars capable of that kind of speed. As far as rigidity of the MG shell, just a few reinforcements added at the right places on the uni-body makes for a good contender. Another thing that Cobra owner don't have is the comfort of the MG, I'm saying that because after sitting behind the steering of one I give that edge to the MG.

I've been reading the forum for awhile now, and I believe that there are enough brains in this group to make any Cobra owner remember what the octagon MG emblem looks like from the rear. I just wish at time that some of the vendors would get together and form a coalition in order to facilitate the conversion choices.

My two cents.

This is just a wild guess on my part, but since LBCs with V8s and Cobras both seem to have a big problem with hooking up, I suspect the additional tire width will give the nod to the Cobra.

"Weight 2460 lbs."

Curtis,

A friend of mine built two of 'em. One for him & later, one for a friend. I really think they were lighter than that. I'm thinking 2100-2200 lbs.

Comfort nod? MGB, definitely. After I sat in a Cobra, it destroyed all the dreams I had of building one. They sure are pretty to look at, though!

Quote:

I really think they were lighter than that.

I copied those specs right off the Factory Five website. Can you think of any reason they'd overstate the car's weight? Factory Five didn't say whether their weight spec was "dry" or "wet", but that wouldn't be enough to account for the discrepancy because 15 gallons times ~6.15 pounds/U.S.-gallon only equals 92.25 pounds.

Yes, you can build an MGB to compete with a Factory 5 “Cobra”. It will likely take more work than the kit, but you can do it. I believe the Factory 5 kits are great kits (I helped a friend build one). I love Cobras and seriously considered a Factory 5 kit for myself.

One question I would ask you is; what is the intended use of the vehicle when completed? I made a priority list before I started my last project. My priorities, in order, were street use, autocross, drag racing and appearance. What are your priorities?

All projects require compromises. I wanted to be able to go anywhere, any time and in almost any weather (I avoid snow if possible). I just couldn’t accept the idea investing that much money and not having roll up windows, a folding top and a usable trunk. The right choice for me was to build my Spitfire instead of the kit. Whatever you decide, enjoy building it (you can’t take too many pictures) and drive the wheels off of it when it’s done.

Hi Phil, what I want at 57 years old is an all around car that performs at best in all of the categories that you’ve mentioned within sensible logic. Curtis gave the best outlook in my opinion on the winning edge of the Cobra kit. It’s a pretty small edge to own for the amount of money you have to spend.

Certainly, the Cobra cannot meet all these categories with streetable comfort, I don’t imagine myself going to one of our meeting in a Cobra and all of a sudden a furious storm hits, second, after driving for awhile in hot summer city traffic I may want to pull up the top and/or turn on the air conditioning to cool off a bit. Drag racing is straight line and (IMO) fair play on both side.

I still believe that the MGB wins in most of the categories mentioned except maybe for autocross, even then if the Cobra driver has an under powered engine he’ll have to catch up in turns. I’ve heard from my friend Jim Stuart that Jim Blackwood has an MG that may stand up to a Cobra.

When I started the thread, my intentions were to invite the premier gear head in our field to listen to their advice on how to approach the leading edge of the Cobra.

As far as looks, the Cobra has an all out “racing” good look, but again the MG in my opinion has an interior much more attractive and comfortable and I’ve also seen some MG conversion that as far as the exterior look would probably hang in there for the (look) argument.

I also own a powerful supercharged Miata which Miata holds a serious benchmark in autocross achievement, but, as far as long distance comfort it doesn’t hold a candle to the sitting comfort of an MGB. When you think about it, the MG is probably the best and most suited vehicle for a successful V8 British car conversion.

Is this a wonderful website or what?!?!?!?

I love your analysis! Well, the Cobra holds a place in automotive history which will never be taken from it. No matter if it is beaten on the track, the strip, the autocross course or the car show, it will always hold that place, dear to the heart of every motorhead. And let's face it, that spot was fairly earned too. So there will always be one justification for owning a Cobra that will never fail. "I want it because it is a Cobra" Fair enough.

But owning a modified LBC is about much more than that. Some builders have sought to match the looks of the Cobra with their car. We've seen some exceptional builds with that goal, simply amazing cars combining good features of both. We've seen cars that can compete on the basis of every performance standard imaginable. But the real goal in building a car is more often not about competing with the Cobra, but about achieving what is most valuable to the builder, and here is where the MGB truly does shine out. It's because, within the limits of an LBC (2 doors, small size, etc) it gives you an almost unlimited blank slate to begin with. The looks are good but can be made as wild as you desire. The handling and ride are acceptable but can be made as good as any other vehicle. The interior is cozy but can be tricked out to your heart's desire. And as for the power? I dare say that we now have far more re-power options than any other car on the planet! Anything from mild to way beyond any resemblance of too much.

No informed person will ever look at your converted MGB and ask you why you didn't buy a Cobra. There are more than adequate reasons. And if competing on the track is near the top of your list, yes, you can compete successfully. The pieces are available to make it happen, whatever you seem to be in need of. And then the really great thing about it is that afterwards if you like you can drive the car home, in comfort and style.

But it isn't a Cobra, it never will be. It's an MGB, and as far as I'm concerned it's the better choice of the two. You take the money you'd pay for the Cobra and put it into the MG and at the end of the day the only advantage the Cobra has left is it's own distinct heritage and mystique. Which MG also has. So it just comes down to a personal choice. The Cobra's name or the MG's comfort? I think that about sums it up.

Jim

Hi Jim, I'm flattered to hear from you, you are held as a great icon on this web's forum and I often enjoy reading your postings. Jim Stuart has spoken many times about your car and the advance technical/personal touch you have put in it. He also told me that you have a brother that can drive one of these high powered machines like nobody's business. Do you really let your brother out drive you (LOL joke)?

Thanks for your insight on this Cobra thread, and you are so right in mentioning that it has earned its place in history with all of credits to the great "Carroll Shelby". Just being able to use it as a benchmark, puts any builder on the right track to success.

Jacques

Curtis,

Like I said, a friend built two Factor Five Cobras. He told me his weighed 21xx lbs.

Same as with our cars, they will vary depending on options.

I was surprised to hear Factory Five say the average build weighs that much. Maybe the newer MK3 frame is heavier?

"Most FFRs weigh in at 2200-2450 depending on the car. I had one that was 1850."

"The FFR Cobras weigh 945kg (2,100lbs.) are equipped with five-speed manual transmissions, will go 0-100 km/h (0-60mph) in four seconds"

Thanks for the kind words Jacques, it's good to be recognized though I'm not sure how much of it is deserved. Pay close attention to the long time visitors to this site, they really know their stuff and are constantly teaching me new things. I really don't know where I'd be without them.

As for brother Dan, it's an honor to have him as my sibling and I can't say enough good things about him. But beat me driving??? Where did that one come from? ;-)

JB

"He also told me that you have a brother that can drive one of these high powered machines like nobody's business. Do you really let your brother out drive you?"

Jim Stuart must have said that to get a rise outta Jim B. Doesn't matter they all 3 drive like Grandmas! ;)


Truthfully, I KNOW Jim B can get down the road.

In general I've always been kind of lukewarm on the cobra kit cars, but I have to admit that the Factory Five operation is pretty impressive. They really approach it from a performance standpoint, rather than a poser "look at me" angle. For me, the mgb gt conversion fits my image of a fun performance car perfectly. BUT, I have to admit that I could see building a Daytona replica someday.

add the GT 40 to my list.......and whole-heartily agree with Carl regarding Cobra ergonomics - deal killer!

Here's an interesting fun fact from "Wicki Cars" that I found out while reading the extensive history of the"Cobra" (start of quote)

The first 75 Cobra Mark I (including the prototype) were fitted with the 260 engine (4.2 L). The remaining 51 Mark I model were fitted with a larger version of the Windsor Ford engine, the 289 in³ (4.7 L) V8. Toward the end of 1962, Alan Turner who was the chief engineer at AC completed a major design change of the car's front end and was able to fit it with Rack and pinion steering while still using transverse leaf springs suspension. The new car went into production in early 1963 and it became known as the Mark II. The steering rack was borrowed from the MGB while the new steering column came from the VW Beetle. About 528 Mark II Cobras were produced to the summer of 1965 (the last US bound Mark II was produced in November 1964). (end of quote)

Obviously, the MGB holds a small but effective role in the Cobra's good handling. It went from a crude steering box to an accurate "rack and pinion". I guess you could say that the Cobra has a small DNA trace of the MGB.

Yes, and in fact so do the reproduction Cobras. The original repro, the Arntz-Butler Cobra used the front suspension from the MGB in it's entirety with only very minor modifications.

JB

Not to take any credit away from the king, but Carroll Shelby was a lucky man, I always thought that he engineered the car right out of the hands of the AC Company but not so; he seemed to also have cashed in on a lot of "trial and error" from other players. Furthermore, with the help of Ford's deep pockets it must have been a blast to keep fine tuning this incredible machine into a world class contender.

Does Jim Stuart know Andy? Maybe that is the brother he is referring to. After all, he is a "professional driver"

Dan B.

"The first 75 Cobra Mark I (including the prototype) were fitted with the 260 engine (4.2 L)"

That, I did know. Saw one live & in person one year at the annual Springtime in the Smokies British car show in Townsend, TN.