[Cassutt Pilot]

The first Cobra replica I ran across was FFR's. Later, a friend mentioned UNIQUE MOTORS. After looking at the two, and their respective frames, it would seem that UNIQUE, with their pancake-like frame would have to depend on the body itself to have sufficient torsional rigidity. I used to have an MG-TC, and when I pulled into a driveway that was steep, I could feel the body twist as I turned up-hill onto it. If they use the body to add this stiffness, they must use the fiberglass as a structural part of the car, which would probably add considerably to the weight. Can anyone tell me if there is any advantage of the UNIQUE Cobra over the FFR? At present, I'm leaning strongly toward the FFR. Thanks.

 

[Roger]

My high school MG-TF did the same thing. At certain angles the doors would stick.

I can jack up any corner of my early FFR and the doors still work. The light carbon body is extremely stiff but adds nothing the chassis. The same can be said of the original aluminum body, it adds nothing. This concept had everything to do with my decision to build an FFR. I like the looks of other Cobra kits but what's beneath the skin doesn't do it for me.

My opinion is not here to berate anyone else's choice. The quality of the new FFR MK 11 at $11,900 is a bargan. So was FFR 1225 at $9,900, that still weighs in at 2080 lbs.

 

[Faststang]

Wrong thread, oops

[ July 21, 2002, 02:28 PM: Message edited by: Faststang ]

 

[Micobrael]

Just a tid bit. The other day I was jacking up the snake(FFR) and got lazy and only jacked her up from under the left tube in the front and the whole front raised as if I was smack dab in the middle no twisting!! COOL! This was a big factor in choosing FFR, That and I saw Dave roll at Run and Gun and they taped it up and kept racing! OH and Dave walked away! Michael

 

[Kostiuk]

Michael, I noticed the same thing. As a matter of fact I put a floor jack under the frame rail under the drivers seat to jack up the rear tire and actually had both drivers side tires off the ground. Front and rear. I've never had a car that does that before.

 

[aumoore]

I can jack my Hunter from under the frame rails that support the floorboard. I do not know if the Unique is the same but it does have a similar frame. I do not think any Cobra Replicas rely on the body for support. The FFR is kind of unique as it supports a very light body with a network of square tubing. I would guess that the tubing, aluminum and thinner fiberglass would be about the same weight as some other Cobra Replicas with a fiberglass tub and body. Remember these cars have very short wheelbases so the frame if built properly will be rigid.

Here is Pete's website showing the Hunter Frame
http://members.cox.net/petescobra/

 

[Wes Tausend]

Cassutt Pilot,

You've struck at the heart of the FFR principle and stated it quite well.

The Unique Motorcars replica is probably as torsionally stiff overall as the FFR but they gave up lightness to do it. If it has any advantage over the FFR it would probably be their lower volume production and the extreme personal customer attention that this fact allows. I visited their factory before I bought my FFR and, for a bit more money up front, Unique provides a product with much more factory finishing done whether one buys the "Deluxe Pallet" kit or not. By all accounts Unique invented customer service and I have never heard of an unhappy customer. Except for the weight and frame design the Unique is very true to the original with its MG and Jag running gear. The suspension has been improved over the years and, like FFR's, I'm sure, is well sorted out now. One of my favorite items, the LeMans top, was once offered and may still be available special order. I think Joe Traut who helps host the Northwest Replica Challenge, has or had one on his Unique.

That said I must go on to say that FFR is nearly the only manufacturer to pay much attention to weight and the performance potential that light weight allows. In this respect they are absolutely the most true to original concept of any replica on the market today at any price. This was the very foundation of the original AC roadsters and paring weight remained a major stumbling block to Shelby's new Series One. Weight was said to be the major factor in the Series One delay, courtesy Mr. Shelby. And he knows what's important for performance (and where a major threat comes from).

Contrary to the conclusion of a popular website that discusses the old square tube vs round tube frame design, I think the 4" round tube still remains a ladder frame improvement from its inception by late '50's and early '60's designers. While it's true that an identical material 4" square tube inherently has greater lateral and vertical deflection resistance, this symmetrical flex is not much of a problem in a short wheelbase car and has a lesser effect on handling than torsional rigidity. And most kits (or rollers) have only a 2" x 4" ribbon 1010 mild steel ladder frame. Besides twisting forces from driveways and high G cornering, torsional rigidity resists frame twisting engine torque. Add to the fact that FFR improved the original (at a slight weight sacrifice) type of round tube by going to .125" wall tube instead of .95" and then threw in higher carbon 1020 steel and there is no contest. The FFR frame represents a nearly perfect blend of light weight yet rigidity. There's more. The new MKII frame has a spaceframe-like reinforced back bone area, similar to the Daytona Coupe frame, that further resists torsional flex and greatly adds to the lateral deflection resistance (in case the riders are quite portly or one wishes to haul a load of sand in the passenger seat

).

When FFR designed their kit they aimed primarily for performance over originality. When it came to the frame they discovered that 4" round tube was originally used because it saved weight and improved performance on the original ladder frame cars of the era. As a matter of fact the original design of ladder frame cars with a minimal "curtain body" such as the AC are hard to improve upon other than as noted at FFR above. That the FFR represents such a pricey similar design underneath as original cars of the era ...is just a side benefit. They are Factory Five Racing Co. not the Factory Five Replica Co. Mark and Dave are performance guys first and foremost with an appreciation for grand engineering. I wouldn't be surprised to someday see one of their creations entered in international competition.

 

[PSB]

I don't think there is much difference in the torsional rigidity between an FFR and most other manufacturers frames. I don't think any of them use the body as a stressed member except to support the body itself. The purpose of the FFR "birdcage" is to support the body, thus allowing for a much thinner and lighter body. By the way, I can jack my Hunter frame up from any corner and have the opposite tire come off the ground also. That's with the engine in, but the body off (I haven't bolted the body down yet, so I've never tried jacking it up with the body on).

If you're picking a kit as torsional rigidity as your main concern, nothing can beat a semi-monocoque frame like JBL's. Check out JBL Motorsports. JBL is more expensive than most, but if an absolutely rock solid frame is what you're looking for, they've got it.

From the JBL website:

[ July 22, 2002, 11:56 AM: Message edited by: Pete Ballentine ]

 

[grumpy]

CP,
The ACJP frame of 90"WB and 2-4" dia tubes as carried on the CSX3*** series and on several other variations are stronger torsionally than a C5 or Z06 ladder style, try jacking them up at similar points, isn't that stiff enough?
Grumpy

[ July 22, 2002, 10:08 AM: Message edited by: grumpy ]

 

[TAZ]

Pete,

That looks well engineered. I was wondering if you could answer a few questions that's not on JBL's website.

1.) How much does it weigh when completed?

2.) What's the wheel base on it?

3.) How big of an engine will it support?

4.) What's the weight distribution?

Thanks,
TAZ

 

[Wes Tausend]

There is not much doubt that the JBL is slightly stiffer than most replica frames but it shares one thing with the majority ...it weighs in at about average. Here one might actually prefer the FFR design which gives up only marginal stiffness and weighs much less. I estimate my FFR frame, aluminum underbody and carbon body to only weigh 350-375 pounds as shipped. My son and I simply picked it up and sidestepped off the trailer with it to unload it. Here is a quote off the JBL website page, http://www.jblmotor.com/JBLchassis.html :
"The total weight of the chassis structure is 418 lbs.
Finished car weight with 351 alloy head motor is 2350 lbs."
I don't know what the JBL body weighs but the total car weight seems about 300 pounds more than Rogers FFR, above. The FFR fiberglass is about 100 pounds more than the carbon.

One might also note that the JBL front suspension is designed to be easily adjustable (from the seat) by using comparatively massive cantilever top arms although these arms don't also gain the prime F1 advantage of removing the shock and spring from the airstream. The Hunter, by contrast, also uses forged aluminum suspension pieces, but very light in a standard configuration, for apparent better unsprung weight than the JBL. Everything is a tradeoff. They're all stiff enough. Final weight is the FFRs forte' .

 

[PSB]

TAZ,

I don't have a JBL, so I'm not going to try to answer those questions, as I might not give you the right info. However, check out Andy Dunn's website of his JBL build, Cobra Lads. Send him an e-mail and I'm sure he'll answer any questions.

I really like my Hunter, but if I had a (much) larger budget, I may have gone with JBL.

Pete

 

[Greg A. Warwick]

The men at JBL are doing some mods so they can run the new generation Ford "MOD" motors. When they can fit the mod engines, the fat block Fords will also fit. The wheel base is 95", they also have proper suspension geometry. Oh, yea, they are coming out with a "Coupe" replica this year. Nice stuff.

 

[Fred Turton]

I enjoyed looking at and reading about the JBL semimonocoque chassis. I note that the car uses "Anti-Roll Bar, Rotary Blade Type, Adjustable." This type of roll bar allows in the cockpit adjustment of roll stiffness of both the front and rear suspension. I have heard of in-cockpit adjustable roll bars, but I have never heard of this type. Does anyone have any information about rotary blade anti-roll bars?

Thanks.

 

[andy dunn]

1.) How much does it weigh when completed?
Chuck Millers JBL weighs something like 2450lbs. I believe the san diego cobra club has scales so one of the members might know exactly. My JBL is little heavier and weighs something like 2550lbs without me in it. I think it weigt depends on the builder to some degree. What is the average FFR weigh? I thought it was closer to 2400lbs? I would guess the average JBL might be around 2500lbs. I know for a fact that my fiberglass body weighed something like 93lbs because I carried it around the driveway often and hoped on the scale with it once (that weight does not include hood or trunk etc). I think FFR builds the lightest cobra, but I think the difference is 100-150lbs lighter than the other choices. The biggest variance in weight in cobras is chassis and then engine choice. I see the fiberglass bodies in most cobras as being fairly close in weight. My guess is that the FFR chassis is 50-100lbs less than other manufacturers, and if a builder choose a 302 mill, then there would be additional weight savings. Thoughts? I think you could also get other manufacturers cars down to 2000lbs, but you have to work at it since you are probably building a race car at that point.

2.) What's the wheel base on it?
95"

3.) How big of an engine will it support?
The current model supports small blocks. As FFR2372 wrote, Dave and Richard are working on adjusting the frame to accept the new trick Ford 4.6L mod dohc engines which are very wide and this would then allow a big block.

4.) What's the weight distribution?
44% Front and 56% Rear Why? Because Richard Hudgins was a racer that drove like a bat out hell coming off the corner. He designed the car to match his style.

By the way, if you ever want to get your weight and bias at home, you might invest in a set of Ruggles' scales.
http://www.tgsi.com/scales.html

I have a set and they come in handy. I need to build a better set of ramps to get onto them though. Now an even better solution is available and I wish I had found these first. Speedway offers a set of mechnical scales around the same price.
http://www.speedwaymotors.com/eCCStoreFront/smi/product_images/Full/010-2.jpg

Fred, here is a nice write up on the bars from the Torborg's site
http://www.jaytorborg.com/anti-roll_bars.htm

You tend to find these driver adjustable blade setups in certain race car classes. I can sometimes find cars with them when searching on google. Carroll Smith mentions them in one of his books.

Here is a description from Richard Hudgin's site. In this first picture the blade is flat and is in the easiest position to bend. It only takes 80lbs of force to bend the blade 1". This would be a soft setting for perhaps a bumpy track or rain.



In this next picture the bar is verticle and very difficult to bend. The same bar now requires over 1000lbs of force to deflect the blade one inch. This might be used on a very smooth or very fast track.


There are a couple of ways to control them. Chuck Miller's car uses two additional mini gear shift like levers that mechanically move a throttle cable and pivot the blades. Most systems use that method. Scott and Richard could not leave well enough alone and decided to make the system electronic. Now the arms are operated via a dash switch that has 10 leds to indicate the current position.

I think the question on chassis stiffness can be settled in 30 seconds and mathematically. To this date, I know of only two manufacturers who even know their chassis overall stiffness. Bob Putnam's ERA and Richard Hudgin's JBL

ERA 2400 lbs per degree.
Body and inner panels add at least an additional 500 lbft/deg

JBL 4375 lbs per degree.
24.5 HZ Standard without cage and stressed engine. The JBL has been tested with both the Beam and Frequency methods for stiffness rating.

I'd be interested in hearing other manufacturers tested stiffness ratings.

Hey! I just found another reference for "blade adjusters". Check out the Skip Barber book "Going Faster". On page 209, there is a great diagram and explanation of cockpit adjustable anti rollbars which they call "blade adjusters"

hope this info was interesting

Andy

[ July 26, 2002, 05:17 PM: Message edited by: andy dunn ]

 

[Fred Turton]

Thanks, Andy.

 

[David Borden]

the mistress is 2250lbs wet with a 302 alum heads, FI, vortech blower, IRS and full interior.

My stock spec racer is 2317lbs wet with a full SCCA GT1 cage and a passenger seat.

Both have a F/R bias about 45/55% give or take a few %.

David