I'm going to say the Ferrari 308 GTS has just as much dive and squat as the Jaguar. They did very little slalom like movement, but perhaps half the Jag's roll there? Decent comparison, the show used 1979-1986 models.
Magnum P.I. Ferrari 308 GTS (flv video) | (Free File Download, File Backup, File Sharing and Publishing) fliiby.com

 

i have a 1977 road&track mag, showing the road course test of a stock XJS and the Group44 XJS race car, of course the race car was much faster!

but the same driver drove both of them and gave hi-praise for the stock XJS.

and pix showed some roll,but said its tires stayed planted quite well.

on my car i use a 3/4" roll bar with poly bushes, and links,on frt.

no rear bar, tried it, it would put the rear out very easily, IT aint no drift car anyway.

if i wanted to go driftin, darn sure wouldnt use an XJS.

shortened springs all around, became stiffer!
new KYB frt, and 4 new Boge on rear.

and as most of you do know , WHEELS & TIRES are where good handling starts,
if you dont have proper wh,tr, any suspension mods wont be justified.

 

a pic of my front bar,3/4", with poly bushes.

Yah! i'm thinkin the exhaust may go, thats back when i was young&dumb!!

shows my frt wh, &tire,, plus nose, i dont care for lips and such, thing stickin down is trany cooler.


and when you finally got everything done on body and suspension, PIX, you can do the engine,, P/S pump is from a Dodge Viper, only 3.5lbs.

and if you guys get really lucky, you may find some VERY rare raised port cylinder heads ,you can tell because they around 3/4" higher or thicker, big improvment in exhaust port flow lines.

 

almost forgot ,actual weight on a digital &calibrated scale 3360lbs, so now you can get busy!
lighter weight increases handling process, like stiffer springs and shocks!

amazing tho, how nice the car rides,,smooooth!

and it could be a little lower, but bump stops are gettin close.

 

Ronbros, Interesting that you say a rear bar puts the rear end out too easily. Remind me—do you have wider tires at the rear as compared to the front?

If you're running equal widths front/back, and a rear bar causes excessive oversteer, it would probably cause just the right amount of oversteer on a car with staggered widths as mine will soon have since the wider rear tires will prevent some of the oversteer...

 

Understeer and oversteer is a product of front and rear roll resistance. Increasing the resistance to roll will reduce the tyres ability to grip. Increasing the front roll resistance ie thicker swaybar or stiffer springs will cause understeer, same in the rear stiffing will cause oversteer, the front and rear need to balanced.

As Ron has cut the springs this has stiffened them thereby the rear probably has enough roll resistance without the swaybar. Also with the cutting has the relationship between front and rear spring rates been retained?

 

Oricalc Crisis Division - Magnum PI Ferrari 308 GTS - YouTube Found a clip of them pushing the Ferrari a little harder. Ok, noticeably flatter now. Watch specifically from 2:00 on.

 

All sizes | Jaguar XJS V12 Vs Porsche 928 S4 1988 (8) | Flickr - Photo Sharing!
CAR magazine from 1988. The Porsche 928 handles a little better, and accelerates faster, but they like the Jaguar better.

EDIT:
OH! Motor trend did one in '83 or '84 with the corvette, porsche 928S, Ferrari 308GTSi, and Jaguar XJ-S. That would be a great read! Anybody have one?

 

I think we're getting into apples and oranges just a bit here.

I've not driven a 308 but have sent some wheel time in a 512BBI....somewhat similar car. If the 308 is anything like the 512, it's a brute compare to the XJS. Much harder suspension, much heavier steering, heavy brakes, heavy clutch, heavy shift....it's a bit like work to drive one until you've reached 40 mph or so. Much more "sports car" than the XJS was ever intended to be.

I suspect the 308 is more refined than the 512, but still.....

Cheers
DD

 

Yes, using it as a reference point. The other end of the scale would be any American full size car from the same time. They pretty much move like a bobble head doll in comparison. Just proving richkaz's point to myself. And trying not to be convinced that stiffer springs may be in order!

 

what may have contributed to rear sliding out, was a custom HI-bias LSD, it would lock to easy, i took the Jag powerlok apart , and it looked a lot like a 50s Corvette positrac LSD,

so just happen to have an old vette unit under the bench(helps to have junk around)

but the vette had one more clutch plate than jag(thinner but more) so i used them,

so without the rear bar(and more miles) it now is fine, will still lock but more controllable.

 

I'm doing my due diligence and going through the forum from front to back, and back to front. In so doing I read this ancient thread with great interest. I recently acquired a 90 V-12 Convertible with 70K miles on the clock (the car is in really nice condition; new Hood and leather seat covers). The ride and steering is no where near as responsive or sharp as my 2000 XKR coupe. I attributed it to the 450 pounds the convert has on the coupe. But you are all saying how "Sublime" the XJ-s rides and how flat it corners. My suspension bushes all look in good condition, the front shocks are Monroe (so replaced at some point) no leaks on the front or rear shocks/dampers. The steering rack bushes "look" like poly replacements but I'm not sure on that. The front sub-frame bushes also "look" okay, and the rears where replaced. I'm sure the springs are original. So what do I do to make it feel more like my XKR? The rack leaks a bit so in the future I'm thinking of replacing it with the ZF aluminum one used on the 93 and up facelift cars (Is that a good idea?) From what you all say; I'll stick with stock rubber control arm suspension bushes. If I can find an OEM rear sway bar, is it worth the expense? (requires new trailing arms with the mount tabs...but it will have new bushes so that's good $100 ea from SNG). SO will Koni, Bilstein, KYB or Boge dampers make a difference? Chime in on which brand is recommended. Do you think after 70K miles the front springs are weak? My Pirelli 600s are 13 years old and show mild cracking in the treads (not the sidewalls though)...to bad because there is lots of tread left. I have a chance to buy 17" Revolvers at a fair price. I know 17's with a 45 sidewall will make it handle better, but will it "spoil" the ride? Even though they are old school 15 inchers, the Lattice wheels are starting to appeal more to me. Please chime in with suggestions....especially Warrjon and ronbros

 

The XJS is quite zippy, bodyroll helps with steering as the rear cage can flex abit, very sharp and grounded through corners, it is absolutely thrilling at any speed

 

You do not really say what you are trying to achieve, so I'll just dive in and let you know what I have done.

The steering on my car is very direct, NO sneeze factor, turn the wheel and the car moves.

I have poly rack and front swaybar bushes these I would recommend. I also have poly upper wishbone bushes these I would not recommend, they make the front end very harsh and un-Jaguar like. I have poly front eye subframe mounts and stock rubber V mounts in the rear of the front subframe.

I have Bilstein all round TWR valving NOT Jaguar, but there are also a lot of other good dampers that are probably cheaper. Stock front springs and heavy duty rear springs 1" front sway bar and no rear bar yet. My car also sits on 16x8 BBS rims with 245/50-16 all around.

Before you commence decide how you want your car to ride and handle, remember without active suspension one is a trade off for the other.

 

I guess I'd like the XJ-S handling to be closer to the XKR. I suppose I didn't realize how good the CATS active dampers really are; which the XJ-S can't duplicate.
More direct steering is what I want, so the poly rack bushes and a ZF rack will be a future upgrade. Perhaps along with a 1" Anti-roll bar.
I also guess, 17" rims with 45 or 50 series tires will make the real difference/improvement in cornering. This is all in the future, after I finish the basics; i.e. new upper and lower bushes and trailing arm bushes. Plus I haven't changed out those cracked rear hubs yet. (Got them off the parts car, but haven't been able to press the hubs out of the carriers yet. New bearings are on the bench. P.S. I found my ABS problem; not the manifold block or dirty solenoids; but the harness itself at the front right has a short...stripped out the harness on the parts car, but yet to go through the pain of routing it in the convertible. My excuse: remodeling the kitchen and built a swim platform for the SeaRay.

 

I have a low mileage (44k) all original car and it handles surprising well - especially at speed. It seems to have exaggerated body roll at lower speeds but if you throw it into a corner on the twisties at moderate to higher speeds it flattens right out and has that Jaguar characteristic of seeming to hunker down and increase traction if that makes any sense (my F type is the same way... just have be going faster to get the effect). An American car of the same size and vintage as the XJS would under steer right off the road off the road in similar circumstance. If I had to choose between the XJS and the F Type I'd take the XJS as its ride is incredibly smooth and stable... much more civilized.

"My Pirelli 600s are 13 years old and show mild cracking in the treads (not the sidewalls though)...to bad because there is lots of tread left."

Ditch those immediately regardless of tread. Tires are meant to last 6-7 years at most without significant decomposition... especially in the sidewalls.

 

In my experience adding a rear bar and upgrading the front bar is worth the effort and expense....and quite possibly will give all the improvement you are looking for. Don't go crazy with the rear bar size. Something along the lines of 13-15 mm will do the trick

Personally, for driving on real world roads, I like stock/soft-ish springs with the anti-roll bar upgrades and high quality shocks and tires. That always does the trick for me.

Lower profile tires generally make the steering crisper....which is fine. But there can be negative trade-offs when you get down to 40-45 series tires....and not just ride quality.

Poly rack bushings are a must.

Always remember that there's more to 'good handling' than just eliminating body roll. Flat, flatter, flattest cornering attitude, if done purely by stiffening the suspension, can eventually swing things to the negative side of compromise...and there's always a compromise.

I have a little 'private test track' that includes turns, bumps, swales...just like the rear world. I can negotiate the course with more confidence in my old Jag than I can in many other more performance-oriented cars. The others may have virtually zero body roll razor-sharp steering but are often a bit twitchy and don't like bumps in the middle of a turn. The Jag is totally undisturbed by such things so I can go faster and faster, more comfortably....even if there's still some body roll.

It all depends what you're looking for. The old Jag suspension responds well to some mild firming-up but be careful what you wish for ! As designed, the suspension and behavior are free of unpleasant vices....something Jaguar managed to pull off more effectively than many others. Even if it seems a bit soft the car probably corners better than you think it does....if all aspects of good cornering/handling are taken into consideration

Cheers
DD

 

Thanks Doug and El Gato, very good synopsis. I haven't cornered it yet at speed. I suppose I have to get rid of those old Pirellis...dang it. P.S. They aren't available anymore in the US. Since I need tires, I have to decide whether to keep her stock with BFG's or Michelins, OR buy the 17" Revolvers (or aftermarket Lattice style) and put 45 to 50 series tires on her... I agree 35-40's are way to low a profile. Mostly I'm looking for "Confidence" at higher speed turns. I guess I'm just not used to the way it handles VS the XKR.

 

Hi,

I have a 92 XJS 4.0 Coupe in Perth, Australia. My Jag's rear seems to be sagging and i plan to change the springs. Mine is the sportspack, but the coils (CBC2793) for this are very expensive (if available) compared to the non sports pack coils (C39692). I was wondering if you had any thoughts/experience on how the ride height and handling might be affected if i fitted the non sports pack coils.

Cheers

Raymond.

 

You will not notice the difference. If you want a firmness-adjustable ride, fit a set of Gaz or AVO adjustable shocks to the new springs.