Design of the Hess & Eisenhardt Convertible
#1
06-23-2012, 10:11 AM
Design of the Hess & Eisenhardt Convertible
I mentioned on my earlier post that my father was one of the engineers who designed the Hess & Eisenhardt XJS convertible. He worked a career as an aeronautical engineer for General Electric, but in the mid-80's he moonlighted for Hess & Eisenhardt on free nights and weekends. Here's some of the stories he tells about working there...
On how they got the Jaguar contract:
In the early 80's H&E did work back then producing armored cars and limousines for high end clients. GM wanted to produce a convertible of their A body series (Oldsmobile Cutlass Ciera, etc.). In almost all cars, the top is a structural member and removing it takes away a significant portion of the structural stiffness and torsional rigidity. In the case of the GM A body series, it was over 90% loss, and due to the structural modifications necessary the usual industry players passed on accepting the contract. H&E picked it up and was able to come up with a design that retained all the structural stiffness and 70% of the torsional rigidity, which was quite a feat. This cemented H&E's reputation for similar contracts in the future.
Meanwhile, Jaguar was having issues as they had no convertible option at the time. Dealers stateside (specifically starting in Miami) were going to local chop shops to have the top cutoff XJS coupes and turned into convertibles. Of course, they were crap jobs, and Jag was concerned these cars were affecting their reputation. Knowing that it would be several years before they could design and tool up for a true factory option, they turned to H&E to produce models for the '86 - '88 year.
On the initial marching orders:
Jaguar had the Mercedes 380 SL firmly in their sights, knowing anyone who would buy the H&E convertible would also walk into a Mercedes showroom and compare the two. So they gave the H&E team a scrapped XJS (supposedly the owner had rolled it several times going well over 100 mph in the Arizona desert) and a rented 380 SL convertible, with instructions not to come back until they had something better than the 380 SL.
Having spent much of that summer driving the Mercedes, dad says that the 380 SL is in no way equal to the XJS, and that the XJS is a superior car in every measurable category...
Why the H&E gas tank is split:
H&E kept an artist on hand to freehand designs. Soon after getting the contract, Jag execs came from England to look at a sketch of the design. The suits from Jag protested that the roof stuck out from the car ('tall stack'), and insisted that it fold flat. When H&E pointed out putting the roof down all the way would mean it would be inside the gas tank, the Jag rep's response was "We hired you to find solutions, not come up with problems. Fix it!"
The solution was to cut the top off the tank. Unfortunately a V12 getting 12-15 mpg requires more than a 10 gallon tank, so they had to put in a second tank. They sourced tanks from a local firm that had long made auxiliary tanks for Ford trucks and the like. After the car had gone in production, and customers later started complaining of fuel vapor smells, they went back to the local firm to discuss the issues. The firm insisted it couldn't be their tank, as no one had ever complained about fuel vapors before, until someone pointed out that their auxiliary tanks were always mounted outside the trucks and in such a manner that it would always empty first (both tanks in the H&E contain fuel almost all the way until empty). If there was a small sealing leak, you would never know it if the tank was outside the car. With the tank inside car body, vapors would have time to accumulate and build...
As we all know, when the '89 factory convertible came out, Jaguar had compromised on their original decision to have the top fold flat. The factory convertibles have a tall stack and single gas tank.
On fuel delivery from the aux tank:
Jaguar was skeptical that the two fuel tank system could support fuel demand under any engine load. So they took the H&E prototype to a government test track near Dayton, Ohio with a professional driver. They filled the tank to the brim and told him to step on it.
2 1/2 hours later the tank was drained completely. Average speed: 149 mph and no fuel delivery issues.
On car rigidity:
Dad's role in the project was to ensure the body stiffness & torsional rigidity were retained. He designed undercar members that created enclosed cylinders when attached to the existing framework. With these attachments, the car retained 102% of both structural rigidity and torsional stiffness while adding approximately 400 lbs of weight. This made for a very stiff convertible! To attempt to dampen body vibration and shaking of the windshield, they also added 20lb weights behind each headlight... however when they demonstrated the cars to the Jaguar corporate reps, the reps referred to the vibrations as 'cowl scuttle' and said it was a desirable feature in a roadster (perhaps because it signifies the car is rigid?).
Incidentally approximately 12 Jaguar test drivers took the H&E out for testing. About half said it was just as good as the coupe, and the other half said they had a slight preference for the H&E roadster.
Misc:
As stated earlier, H&E was used to supplying high end clients (Secret Service, etc.). H&E convertibles were made by modifying factory cabriolets, which required some repainted after cutting and welding. H&E actually had to 'dumb down' it's painting operation a bit to ensure the portions they painted over matched the factory.
Dad drove quite a few XJS's in the course of designing the H&E convertible. He said that all were fast, but some were scary fast and there was some noticeable variation in ones from the factory. The original model that had been rolled stood out in particular. He's not sure what modifications would have been done to cause such a performance change, but he said one member of the engineering team thought it had a modified ECU.
Cheers,
Will
On how they got the Jaguar contract:
In the early 80's H&E did work back then producing armored cars and limousines for high end clients. GM wanted to produce a convertible of their A body series (Oldsmobile Cutlass Ciera, etc.). In almost all cars, the top is a structural member and removing it takes away a significant portion of the structural stiffness and torsional rigidity. In the case of the GM A body series, it was over 90% loss, and due to the structural modifications necessary the usual industry players passed on accepting the contract. H&E picked it up and was able to come up with a design that retained all the structural stiffness and 70% of the torsional rigidity, which was quite a feat. This cemented H&E's reputation for similar contracts in the future.
Meanwhile, Jaguar was having issues as they had no convertible option at the time. Dealers stateside (specifically starting in Miami) were going to local chop shops to have the top cutoff XJS coupes and turned into convertibles. Of course, they were crap jobs, and Jag was concerned these cars were affecting their reputation. Knowing that it would be several years before they could design and tool up for a true factory option, they turned to H&E to produce models for the '86 - '88 year.
On the initial marching orders:
Jaguar had the Mercedes 380 SL firmly in their sights, knowing anyone who would buy the H&E convertible would also walk into a Mercedes showroom and compare the two. So they gave the H&E team a scrapped XJS (supposedly the owner had rolled it several times going well over 100 mph in the Arizona desert) and a rented 380 SL convertible, with instructions not to come back until they had something better than the 380 SL.
Having spent much of that summer driving the Mercedes, dad says that the 380 SL is in no way equal to the XJS, and that the XJS is a superior car in every measurable category...
Why the H&E gas tank is split:
H&E kept an artist on hand to freehand designs. Soon after getting the contract, Jag execs came from England to look at a sketch of the design. The suits from Jag protested that the roof stuck out from the car ('tall stack'), and insisted that it fold flat. When H&E pointed out putting the roof down all the way would mean it would be inside the gas tank, the Jag rep's response was "We hired you to find solutions, not come up with problems. Fix it!"
The solution was to cut the top off the tank. Unfortunately a V12 getting 12-15 mpg requires more than a 10 gallon tank, so they had to put in a second tank. They sourced tanks from a local firm that had long made auxiliary tanks for Ford trucks and the like. After the car had gone in production, and customers later started complaining of fuel vapor smells, they went back to the local firm to discuss the issues. The firm insisted it couldn't be their tank, as no one had ever complained about fuel vapors before, until someone pointed out that their auxiliary tanks were always mounted outside the trucks and in such a manner that it would always empty first (both tanks in the H&E contain fuel almost all the way until empty). If there was a small sealing leak, you would never know it if the tank was outside the car. With the tank inside car body, vapors would have time to accumulate and build...
As we all know, when the '89 factory convertible came out, Jaguar had compromised on their original decision to have the top fold flat. The factory convertibles have a tall stack and single gas tank.
On fuel delivery from the aux tank:
Jaguar was skeptical that the two fuel tank system could support fuel demand under any engine load. So they took the H&E prototype to a government test track near Dayton, Ohio with a professional driver. They filled the tank to the brim and told him to step on it.
2 1/2 hours later the tank was drained completely. Average speed: 149 mph and no fuel delivery issues.
On car rigidity:
Dad's role in the project was to ensure the body stiffness & torsional rigidity were retained. He designed undercar members that created enclosed cylinders when attached to the existing framework. With these attachments, the car retained 102% of both structural rigidity and torsional stiffness while adding approximately 400 lbs of weight. This made for a very stiff convertible! To attempt to dampen body vibration and shaking of the windshield, they also added 20lb weights behind each headlight... however when they demonstrated the cars to the Jaguar corporate reps, the reps referred to the vibrations as 'cowl scuttle' and said it was a desirable feature in a roadster (perhaps because it signifies the car is rigid?).
Incidentally approximately 12 Jaguar test drivers took the H&E out for testing. About half said it was just as good as the coupe, and the other half said they had a slight preference for the H&E roadster.
Misc:
As stated earlier, H&E was used to supplying high end clients (Secret Service, etc.). H&E convertibles were made by modifying factory cabriolets, which required some repainted after cutting and welding. H&E actually had to 'dumb down' it's painting operation a bit to ensure the portions they painted over matched the factory.
Dad drove quite a few XJS's in the course of designing the H&E convertible. He said that all were fast, but some were scary fast and there was some noticeable variation in ones from the factory. The original model that had been rolled stood out in particular. He's not sure what modifications would have been done to cause such a performance change, but he said one member of the engineering team thought it had a modified ECU.
Cheers,
Will
Last edited by macboots; 06-24-2012 at 09:58 AM. Reason: spelling/grammar
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#2
06-23-2012, 02:59 PM
That is some great information! Thanks for sharing. If you remember any more stories or information please add to the thread. I think the H&E convertibles are really nice, and the fact that the top goes all the way down really enhances the looks.
Please post more pics of your car. That is really cool that you have a car your dad worked on and helped design.
Thanks again,
Eric
Please post more pics of your car. That is really cool that you have a car your dad worked on and helped design.
Thanks again,
Eric
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donaldmcclane (03-26-2016)
#4
06-23-2012, 10:25 PM
GM wanted to produce a convertible of their A body series (Oldsmobile Cutlass Ciera, etc.).
but since neither one is a Jag, i could care less either way.
Last edited by M90power; 06-23-2012 at 10:32 PM.
#5
06-24-2012, 08:14 AM
A convertible Cutlass Ciera. Forgive me for not being disappointed in the failure of that project. The only thing worse than getting behind an octogenarian on her way home from bingo would be getting behind a distracted, sunburnt octogenarian.
I really enjoyed reading this, love all the behind-the-scenes stories!
I really enjoyed reading this, love all the behind-the-scenes stories!
#6
06-24-2012, 09:46 AM
http://en.wikipedia.org/wiki/GM_A_platform_(FWD)
Cheers,
Will
Last edited by macboots; 06-24-2012 at 09:50 AM.
#7
06-24-2012, 09:48 AM
http://www.flickr.com/photos/9826125@N06/4876808111/http://www.flickr.com/photos/9826125@N06/4876808111/ by http://www.flickr.com/people/9826125@N06/, on Flickr
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#8
06-24-2012, 10:23 AM
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Nor I....but it does take me on a stroll down memory lane :-)
For ages the RWD mid-size Cutlass, Skylark, LeMans, etc were the A-body cars. When the mid-size FWD models were rolled out the still-in-production RWD mid-size cars were re-designated G-body and the new FWD models took on the A-body designation.
The "compact" FWD cars from GM were X-body (Olds Omega, for example) and N-body (Buick Somerset, for example)
It all got very confusing in the 80s. Oldsmobile put the almost-good-as-gold "Cutlass" nameplate on A,G, and N body cars causing no end to the confusion. Some names previously reserved for the fullsize B/C body cars were now used on the smaller G-body...Bonneville being one example.
The full size models (LeSabre, Delta 88, Electra, etc) became smaller, FWD cars and were designated C body (that designation previously used on RWD platforms) and H body. The last of the true "big" RWD GM cars either kept the B-body designation or were given a new designation of D-body.
The "nameplate engineering" was a real mess back then
Cheers
DD
Last edited by Doug; 06-24-2012 at 10:28 AM.
#9
06-24-2012, 10:29 AM
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I mentioned on my earlier post that my father was one of the engineers who designed the Hess & Eisenhardt XJS convertible. He worked a career as an aeronautical engineer for General Electric, but in the mid-80's he moonlighted for Hess & Eisenhardt on free nights and weekends. Here's some of the stories he tells about working there...
Thanks for the enjoyable reading and info -)
Cheers
DD
#11
07-18-2012, 04:22 PM
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This is a great story about the work your dad wasdoing. Hess & Eisenhardt had a longhistory. I have been following the conversionsthey did for a long time. Regarding theCiera, I spoke with a Ciera convertible owner several years back that hadgotten build counts. They made 814 ofthem from ’83 to ’86. They also convertedthe similar Century, Celebrity and Pontiac 6000. During the ‘80s, they also converted the late‘70s DeVille, ’79-85 Eldorado/Riviera/Toronado, and a few MonteCarlo/Regal/Grand Prix.
H&E was also associated with S/S and Superior Coachbuilding limos and funeral cars.
I have always been curious what happened to H&E in thelate ‘80s. For some reason, all theconvertibles being built by H&E changed over to a company named “Car Craft”in 1986. Do you know what happened, orwhy this happened? For ’86 and later, noother Hess & Eisenhardt named convertibles were built except theJaguar. Then, once the Jaguar conversionwas moved to the Jaguar factory in ’89, H&E completely disappeared from theconvertible scene, though Car Craft badged cars continued until 1991. I have an ’87 Car Craft dealer newsletterthat makes no mention about H&E. Were they split into two separate companies? Do you know the relationship between H&Eand Car Craft?
H&E was also associated with S/S and Superior Coachbuilding limos and funeral cars.
I have always been curious what happened to H&E in thelate ‘80s. For some reason, all theconvertibles being built by H&E changed over to a company named “Car Craft”in 1986. Do you know what happened, orwhy this happened? For ’86 and later, noother Hess & Eisenhardt named convertibles were built except theJaguar. Then, once the Jaguar conversionwas moved to the Jaguar factory in ’89, H&E completely disappeared from theconvertible scene, though Car Craft badged cars continued until 1991. I have an ’87 Car Craft dealer newsletterthat makes no mention about H&E. Were they split into two separate companies? Do you know the relationship between H&Eand Car Craft?
#12
07-27-2012, 08:52 AM
#13
07-31-2012, 08:16 AM
Hess & Eisenhardt
Being the owner of an 87 Hess & Eisenhardt I did a bit of investigation on the car. Without being tedious I will cut to the chase: Misters Hess & Eisenhardt were both getting up in age by the time of the Jag contract and had been slowly selling off pieces of the company (with the stipulation that whoever bought that part of the company had to take the employees with it so they would not lose their jobs). The company, by 1992, was completely out of business. Eisenhardt died in 1988 and Hess died in 2000. There is a good site with info about the company at: Hess & Eisenhardt, Willard C. Hess, Emil E. Hess, Charles A. Eisenhardt Sr., JFK limousine, Harry Truman - CoachBuilt.com
As an addendum: Contrary to numerous claims as to how many Hess & Eisenhardt XJS Jags were produced, there was an 18 month contract which included research and development as well as production of the vehicles. The contract started in 1986 and ended in 1988. Total known output was not the 2100 or the 2000 units stated all over the place but was 838 units. H&E was not a major corporation by the time of the Jag contract but was greatly downsized and I think the Jag contract was the last major contract H&E had before closing their doors.
Schoe
As an addendum: Contrary to numerous claims as to how many Hess & Eisenhardt XJS Jags were produced, there was an 18 month contract which included research and development as well as production of the vehicles. The contract started in 1986 and ended in 1988. Total known output was not the 2100 or the 2000 units stated all over the place but was 838 units. H&E was not a major corporation by the time of the Jag contract but was greatly downsized and I think the Jag contract was the last major contract H&E had before closing their doors.
Schoe
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08-14-2012, 06:03 PM
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#15
03-03-2014, 07:05 PM
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#16
03-03-2014, 11:01 PM
good read. thank you for sharing
I'm normally a coupe guy but i wanted the jag in the convertible because i just like the lines better.
I'm normally a coupe guy. mine is not a h/e convertible but i imagine that a lot of the h/e design was carried on by jag. the first time i pitched my xjs hard threw a set of corners the rigidity of the chassis quite impressed me for being a rag top. even at the breaking point of traction the chassis remained stiffer than a lot of sporty coupes iv driven. although handling is a bit sub par compared to modern sports cars. for the time period it was manufactured I'm quite impressed with its cornering and road holding ability's
I'm normally a coupe guy but i wanted the jag in the convertible because i just like the lines better.
I'm normally a coupe guy. mine is not a h/e convertible but i imagine that a lot of the h/e design was carried on by jag. the first time i pitched my xjs hard threw a set of corners the rigidity of the chassis quite impressed me for being a rag top. even at the breaking point of traction the chassis remained stiffer than a lot of sporty coupes iv driven. although handling is a bit sub par compared to modern sports cars. for the time period it was manufactured I'm quite impressed with its cornering and road holding ability's
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03-04-2014, 04:10 PM
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#18
10-23-2018, 12:43 PM
Excellent description
Hi,
Have a Jaguar XJS 1988 modified by H&E.
Bought the car from US with major issues on exactly the area modied by Hess. Is now being worked at by an experienced welder. All what described in this posting is there,
- cylinder from one side to other in the back replacing rear seats. Very strong and looks heavy.
- Under the sill is an add on bar bolted to sill with screws.
- repainted areas with issues
Those modifications are unfortunately killing points for not mantained car as they tend to get filled with water and rust is getting through the sill and also in the area where the radius arm connects to the chassis. This also because all is repainted (worst than factory paint).and the chassis is higly modified in this area where already the coupes are sensitive.
Good point is that the car is simple and easy to fix by a good welder with modern welding techniques. With the protective paint available today also the protection could last far more.
It is a nice car. Would add photos soon.
Have a Jaguar XJS 1988 modified by H&E.
Bought the car from US with major issues on exactly the area modied by Hess. Is now being worked at by an experienced welder. All what described in this posting is there,
- cylinder from one side to other in the back replacing rear seats. Very strong and looks heavy.
- Under the sill is an add on bar bolted to sill with screws.
- repainted areas with issues
Those modifications are unfortunately killing points for not mantained car as they tend to get filled with water and rust is getting through the sill and also in the area where the radius arm connects to the chassis. This also because all is repainted (worst than factory paint).and the chassis is higly modified in this area where already the coupes are sensitive.
Good point is that the car is simple and easy to fix by a good welder with modern welding techniques. With the protective paint available today also the protection could last far more.
It is a nice car. Would add photos soon.
#19
11-25-2018, 01:08 PM
Hi Will,
Do you (or any other fellow here) know by any chance who actually produced the soft top of the Jaguar XJS modified by Hess?
If they are still on business I would prefer to order a new top from them. Have seen on a site ( XJS Data - SAJNV5843FC119665 - Jaguar XJS information, articles, photos and register) a reference to Robbins.
Thanks
Do you (or any other fellow here) know by any chance who actually produced the soft top of the Jaguar XJS modified by Hess?
If they are still on business I would prefer to order a new top from them. Have seen on a site ( XJS Data - SAJNV5843FC119665 - Jaguar XJS information, articles, photos and register) a reference to Robbins.
Thanks
#20
01-25-2021, 04:03 PM
XJS-r
I mentioned on my earlier post that my father was one of the engineers who designed the Hess & Eisenhardt XJS convertible. He worked a career as an aeronautical engineer for General Electric, but in the mid-80's he moonlighted for Hess & Eisenhardt on free nights and weekends. Here's some of the stories he tells about working there...
On how they got the Jaguar contract:
In the early 80's H&E did work back then producing armored cars and limousines for high end clients. GM wanted to produce a convertible of their A body series (Oldsmobile Cutlass Ciera, etc.). In almost all cars, the top is a structural member and removing it takes away a significant portion of the structural stiffness and torsional rigidity. In the case of the GM A body series, it was over 90% loss, and due to the structural modifications necessary the usual industry players passed on accepting the contract. H&E picked it up and was able to come up with a design that retained all the structural stiffness and 70% of the torsional rigidity, which was quite a feat. This cemented H&E's reputation for similar contracts in the future.
Meanwhile, Jaguar was having issues as they had no convertible option at the time. Dealers stateside (specifically starting in Miami) were going to local chop shops to have the top cutoff XJS coupes and turned into convertibles. Of course, they were crap jobs, and Jag was concerned these cars were affecting their reputation. Knowing that it would be several years before they could design and tool up for a true factory option, they turned to H&E to produce models for the '86 - '88 year.
On the initial marching orders:
Jaguar had the Mercedes 380 SL firmly in their sights, knowing anyone who would buy the H&E convertible would also walk into a Mercedes showroom and compare the two. So they gave the H&E team a scrapped XJS (supposedly the owner had rolled it several times going well over 100 mph in the Arizona desert) and a rented 380 SL convertible, with instructions not to come back until they had something better than the 380 SL.
Having spent much of that summer driving the Mercedes, dad says that the 380 SL is in no way equal to the XJS, and that the XJS is a superior car in every measurable category...
Why the H&E gas tank is split:
H&E kept an artist on hand to freehand designs. Soon after getting the contract, Jag execs came from England to look at a sketch of the design. The suits from Jag protested that the roof stuck out from the car ('tall stack'), and insisted that it fold flat. When H&E pointed out putting the roof down all the way would mean it would be inside the gas tank, the Jag rep's response was "We hired you to find solutions, not come up with problems. Fix it!"
The solution was to cut the top off the tank. Unfortunately a V12 getting 12-15 mpg requires more than a 10 gallon tank, so they had to put in a second tank. They sourced tanks from a local firm that had long made auxiliary tanks for Ford trucks and the like. After the car had gone in production, and customers later started complaining of fuel vapor smells, they went back to the local firm to discuss the issues. The firm insisted it couldn't be their tank, as no one had ever complained about fuel vapors before, until someone pointed out that their auxiliary tanks were always mounted outside the trucks and in such a manner that it would always empty first (both tanks in the H&E contain fuel almost all the way until empty). If there was a small sealing leak, you would never know it if the tank was outside the car. With the tank inside car body, vapors would have time to accumulate and build...
As we all know, when the '89 factory convertible came out, Jaguar had compromised on their original decision to have the top fold flat. The factory convertibles have a tall stack and single gas tank.
On fuel delivery from the aux tank:
Jaguar was skeptical that the two fuel tank system could support fuel demand under any engine load. So they took the H&E prototype to a government test track near Dayton, Ohio with a professional driver. They filled the tank to the brim and told him to step on it.
2 1/2 hours later the tank was drained completely. Average speed: 149 mph and no fuel delivery issues.
On car rigidity:
Dad's role in the project was to ensure the body stiffness & torsional rigidity were retained. He designed undercar members that created enclosed cylinders when attached to the existing framework. With these attachments, the car retained 102% of both structural rigidity and torsional stiffness while adding approximately 400 lbs of weight. This made for a very stiff convertible! To attempt to dampen body vibration and shaking of the windshield, they also added 20lb weights behind each headlight... however when they demonstrated the cars to the Jaguar corporate reps, the reps referred to the vibrations as 'cowl scuttle' and said it was a desirable feature in a roadster (perhaps because it signifies the car is rigid?).
Incidentally approximately 12 Jaguar test drivers took the H&E out for testing. About half said it was just as good as the coupe, and the other half said they had a slight preference for the H&E roadster.
Misc:
As stated earlier, H&E was used to supplying high end clients (Secret Service, etc.). H&E convertibles were made by modifying factory cabriolets, which required some repainted after cutting and welding. H&E actually had to 'dumb down' it's painting operation a bit to ensure the portions they painted over matched the factory.
Dad drove quite a few XJS's in the course of designing the H&E convertible. He said that all were fast, but some were scary fast and there was some noticeable variation in ones from the factory. The original model that had been rolled stood out in particular. He's not sure what modifications would have been done to cause such a performance change, but he said one member of the engineering team thought it had a modified ECU.
Cheers,
Will
On how they got the Jaguar contract:
In the early 80's H&E did work back then producing armored cars and limousines for high end clients. GM wanted to produce a convertible of their A body series (Oldsmobile Cutlass Ciera, etc.). In almost all cars, the top is a structural member and removing it takes away a significant portion of the structural stiffness and torsional rigidity. In the case of the GM A body series, it was over 90% loss, and due to the structural modifications necessary the usual industry players passed on accepting the contract. H&E picked it up and was able to come up with a design that retained all the structural stiffness and 70% of the torsional rigidity, which was quite a feat. This cemented H&E's reputation for similar contracts in the future.
Meanwhile, Jaguar was having issues as they had no convertible option at the time. Dealers stateside (specifically starting in Miami) were going to local chop shops to have the top cutoff XJS coupes and turned into convertibles. Of course, they were crap jobs, and Jag was concerned these cars were affecting their reputation. Knowing that it would be several years before they could design and tool up for a true factory option, they turned to H&E to produce models for the '86 - '88 year.
On the initial marching orders:
Jaguar had the Mercedes 380 SL firmly in their sights, knowing anyone who would buy the H&E convertible would also walk into a Mercedes showroom and compare the two. So they gave the H&E team a scrapped XJS (supposedly the owner had rolled it several times going well over 100 mph in the Arizona desert) and a rented 380 SL convertible, with instructions not to come back until they had something better than the 380 SL.
Having spent much of that summer driving the Mercedes, dad says that the 380 SL is in no way equal to the XJS, and that the XJS is a superior car in every measurable category...
Why the H&E gas tank is split:
H&E kept an artist on hand to freehand designs. Soon after getting the contract, Jag execs came from England to look at a sketch of the design. The suits from Jag protested that the roof stuck out from the car ('tall stack'), and insisted that it fold flat. When H&E pointed out putting the roof down all the way would mean it would be inside the gas tank, the Jag rep's response was "We hired you to find solutions, not come up with problems. Fix it!"
The solution was to cut the top off the tank. Unfortunately a V12 getting 12-15 mpg requires more than a 10 gallon tank, so they had to put in a second tank. They sourced tanks from a local firm that had long made auxiliary tanks for Ford trucks and the like. After the car had gone in production, and customers later started complaining of fuel vapor smells, they went back to the local firm to discuss the issues. The firm insisted it couldn't be their tank, as no one had ever complained about fuel vapors before, until someone pointed out that their auxiliary tanks were always mounted outside the trucks and in such a manner that it would always empty first (both tanks in the H&E contain fuel almost all the way until empty). If there was a small sealing leak, you would never know it if the tank was outside the car. With the tank inside car body, vapors would have time to accumulate and build...
As we all know, when the '89 factory convertible came out, Jaguar had compromised on their original decision to have the top fold flat. The factory convertibles have a tall stack and single gas tank.
On fuel delivery from the aux tank:
Jaguar was skeptical that the two fuel tank system could support fuel demand under any engine load. So they took the H&E prototype to a government test track near Dayton, Ohio with a professional driver. They filled the tank to the brim and told him to step on it.
2 1/2 hours later the tank was drained completely. Average speed: 149 mph and no fuel delivery issues.
On car rigidity:
Dad's role in the project was to ensure the body stiffness & torsional rigidity were retained. He designed undercar members that created enclosed cylinders when attached to the existing framework. With these attachments, the car retained 102% of both structural rigidity and torsional stiffness while adding approximately 400 lbs of weight. This made for a very stiff convertible! To attempt to dampen body vibration and shaking of the windshield, they also added 20lb weights behind each headlight... however when they demonstrated the cars to the Jaguar corporate reps, the reps referred to the vibrations as 'cowl scuttle' and said it was a desirable feature in a roadster (perhaps because it signifies the car is rigid?).
Incidentally approximately 12 Jaguar test drivers took the H&E out for testing. About half said it was just as good as the coupe, and the other half said they had a slight preference for the H&E roadster.
Misc:
As stated earlier, H&E was used to supplying high end clients (Secret Service, etc.). H&E convertibles were made by modifying factory cabriolets, which required some repainted after cutting and welding. H&E actually had to 'dumb down' it's painting operation a bit to ensure the portions they painted over matched the factory.
Dad drove quite a few XJS's in the course of designing the H&E convertible. He said that all were fast, but some were scary fast and there was some noticeable variation in ones from the factory. The original model that had been rolled stood out in particular. He's not sure what modifications would have been done to cause such a performance change, but he said one member of the engineering team thought it had a modified ECU.
Cheers,
Will