I just found a web site for Paramount Performance and see that they offer an aftermarket LSD. Does anyone here have any experience/knowledge regarding this LSD?

Mark

 

The LSD is made by Quaife in the UK. They had an exclusive on the unit for a period of time, it was tied into a commitment to purchase so many a year. Here is a link in the US.

Applications Page

 

Thanks for the link, I was able to find a place in the US that sells them for about $800 less than the place in the UK wanted.

Has anyone hear ever used one of the LSDs? How good are they? Reliable?

Mark

 

Quaife are probably the best diffs money can buy.

 

Have used the Quaife for some time, and althoug I was happy with it and are probably the easiets to drive with, I preffer clutch type ones, is a bit more involving ;-)

 

Thanks, but I have a question. What exactly do you mean by "easiest to drive with" and "involving"?

Mark

 

The Quaife allows the rear wheels to have different speeds, which makes it easy to corner. The clutch types will lock the wheels pending of the amount of power you apply (and also of course pending the lsd settings like ramp angle and clutch types). I like the latter as not only can you slide when you like, you need play with your throttle more to balance it out, which makes it more involving (=more fun for me).

 

Thanks avos, I believe that I will get this LSD. I appriciate your insight.

Mark

 

+1 for what avos said

 

I have decided to do this mod within the next few weeks. Unfortunately, it appears that I cannot change the axial ratio at the same time as this would require the ECM to be reprogrammed. Back, during my misspent youth, I had a Mazda RX7 that I heavily modified (Duel Progressive Weber Carbs, performance exhaust, and new axial ratio). While loosing some top end speed, going from a stock 3.93 to a 4.09 made a big difference in the car's quickness. As the XKR has it's top end artificially limited, this same mod could increase the XKRs quickness without reducing it's achievable top end.

Mark

 

I like that idea simply because I will probably never again come near the 155 mph top speed. I hit 146 once, and that was scary as hell in a convertible with the top down. I can see myself popping it up to 100 every once in a while, but I don't need to have extra RPMs at the top.

Why would a shorter axle ratio require the ECM to be reflashed? It seems like that would be no different than installing smaller or larger wheels and tires.

 

I think what he meant that something needs to be done in order to keep the speedometer accurate. Back when I had my Corvette, for a few hundred bucks you could get a handheld programmer that among other things, remapped fuel curve, turned radiator fans on sooner, changed shift points, and also adjusted the speedometer to accommodate changes in gear ratio when changing from stock. Similarly going to oversize tires will result in the speedometer reading a lower speed than you are actually going. In the "old" days you would adjust for gear ratio changes/tire sizes was done by changing a small gear in the cable that went from the speedometer to the transmission. These days it is accomplished by programming the ECU.

Which for the umpteenth time makes me ponder and lament why simple hand-held or laptop driven programmers are available for so many other cars but not for us.

Doug

 

You are correct that changing the axial ratio will affect the speedometer but that is not what I meant. From reading other posts in this forum, it is my understanding that if you install a different axial ratio and then do not reprogram the ECM, the car will go into limp home mode. I did not fully understand the explanation for this behaviour but you can read it for yourself in the following thread:

https://www.jaguarforums.com/forum/j...d-31450/page2/

posts 35, 36, and 38 talk about the problem. It is also discussed in a number of other threads. If a solution could be figured out, this would be a great mod.

Mark

 

It’s the TCM that has to be re-programmed, as that one uses the wheel speed compared to input shaft speed to check if the gearbox is in the right gear/not slipping. By altering the rear ratio it will go into limp mode. As the wheel diameter is not changing the tacho doesn’t have to change.

Personally I have mixed feelings about going for a higher gear ratios, you will get more torque to the wheels, but higher gear ratios will reduce hp a little (due to more friction), possibly add another shift (pending on the range you use it), and also affect fuel consumption (I drive just too much, so fuel consumption counts for me).

You would need to make a custom set of gears to use with the original diff & quaife, and I aven't found anyone yet that can make these at reasonable prices. All you can do now is use the lsd units (clutch type) from older jags, Jaxkr has gone this way.

 

I will have a quaife in my track car and I will be changing the ratios to a 4.09 maybe even a 4.25, quaife will make a new crownwheel and pinion for you, not cheap about the same price as the carrier $1200 a piece, but I have no TCM, that went in the bin

There is another way, by fitting an XJ LSD, these swap quite easy, you will also need to change a section of the subframe as the nose of the diff is offset, you will also have to machine a different flange to meet up with the prop. I know quite a few that have done it, I beleive jaxkr has.
The TCM needs reprogramming for all the reasons Avos has said

 

It is true the TCM needs to be reprogrammed. I have gone thru the full range of diff changes, first by fitting a 3.27 ratio which is factory fitted to a Mexican market XK8. This will bolt inno mods. I have a TCM programmed for this ratio & a used diff all you need is to install the Quaofe. The next was to install a 3.58 LSD as fitted to a 6 cyl XJR this involves a new mounting plate for the front of the diff as well as modifing the center mount of the prop shaft. This I have recently sold. The current setup in the car is a 3.73 LSD also from a 6 cyl XJR. This diff had to have the pinion modified to fit. I would recomend at the same time you install the blue top solenoids in your transmission. This is a great improovement in shift quality. The higher the ratio you go the shorter the shift is from 1-2 I have found in traffic it is best not to use sport mode.

 

How did you reprogram the TCM? How much of a difference did the 3.27 ratio make? Do I understand correctly that you still have this setup? If so, are you willing to sell it? How much do you want for it?

Mark

 

The TCM had to be sent to Germany to be reprogrammed. I paid $2000. each time I had one reprogrammed. I do have the 3.27 ratio setup for sale. Please post contact info.

 

How much of a difference did the 3.27 ratio make?

 

In principle it adds about 8% more torque to the wheels (minus a slight loss for more friction), so probably noticeable, but have never driven with a different ratio so I can't comment on that.