Hi Everyone,

So recently I decided the best next area to pay attention to on my car would be the rear suspension/handing, specifically the stiffness on cornering. Rationally I went looking for rear sway anti-roll upgrades such as bushes and bars themselves.

Powerhouse makes great stuff and they sell a bar with a 35% increase. I was hoping I could find a little bit more aggressive bar considering that an XJ8 does not even have a rear bar and the XJR bar jumps in with a torsional stiffness of 458lbs/in according to my calculations. Call me crazy but 100-150% seemed more suited considering the regular 8s don't come equipped at all and they handle okay. That was my nutty reasoning. And I couldn't find a stiffer bar, so time for some fun.

The stock bar is 16mm solid steel, and according to my calculations with PH's 35% increase their bar being 18mm would have to be 18mm with 3.25mm walls. For me to about double the stiffness plus some there are plenty of pipe diameter/wall thickness combinations you can go with, but I decided to make a 24mm with 1.5mm walls which comes to 960lbs/in or a 21mm bar with 3mm walls @ 1006lbs/in. Remember these are my calculations, prob aren't perfect. The thin wall 24mm was weld reinforced and I had to shorten a straight and re-weld which clearly stiffened it up even more. In all honesty the 24mm 1.5mm thin wall feels stiffer than the 21mm 3mm wall which is rated stiffer. I called the 24mm the "ugly" because well.....it was.

Some of what I just said is why I have stuck with the 21mm 3mm wall 1006lbs/in bar. No harshness on bumps/potholes that is noticed compared to the stock bar, which was somewhat of a surprise to me, but then again I have never added or upgraded a rear sway on a car with such a high curb weight speaking relatively.

My wife couldn't tell the difference on a little cruise and under normal driving conditions honestly I cannot either. Now under spirited driving the rear is much more poised while cornering and it really inspires me with a bit more confidence going into a corner (I think i've been driving my MG too much).

I still have to test "coming out of a corner" and if over steer will be escalated to unsafe levels and if I will need to tone down the lb stiffness. During the first few days I have noticed you can kick out the rear a bit easier on throttle but it doesn't appear at a dangerous level. Still need more testing. I have to mention I don't know how the transfer of torque among the bar is affected with longer grade 8 bolts accompanying the 21mm bar, but it feels good so i'm sticking with it.

I am running prothane bushings with these bars along with new replacement link bushings. The oem 16mm bar bushings and links were replaced only 1 year ago.

In the pic the oem is closest, the 24mm "the ugly" is in the middle, and the 21mm 3mm wall is farthest. I will update after auto-x this weekend so I can evaluate the handling a bit better.

 

Hmm my XJ8 came with a bar from the factory!? It isn't a sport nor an XJR... Nearly a well equipped base model.

 

Sorry, XJR and XJ Sport models both came with rear sway option but not the supercharged VDP from my knowledge. No base XJ8 in the US has one from what i've seen but who knows?
http://www.jaguarclassicparts.com/uk...arged-xj-sport

UPDATE: Ordered Prothane sway link grommets to match the sway mount bushings and went ahead and ordered front Prothane sway mount bushings to match and trial, I think others may be running Prothane up front already