What other model differentials will fit the xk8.
 

Curious about doing a differential swap to a more favorable gear in the differential.
I've heard the 3.54 from the XJs might have similar internals, but does anyone know of another option??

XK8RACER???

Not similar at all I am afraid, but you can fit a XJ LSD (Powerlok)
You can swap the whole diff, it will bolt in the difference is the XJ diff is offset by about an 1", so you will need to change the front plate of the rear subframe.
Because the diff is offset you will also need to fit an XKR prop, this is a 2 piece item which will allow for the slight angle.
Antoher problem is if you change the ratio too much you will need to get the TCM reprogrammed, that is not cheap.

Thanks so much for the help.
I found a reference that the internals are Dana 44?
If that's true, what's to stop you from using a Jeep ring and pinion?
What year XJ will bolt in? What gear ratios are standard?

I want to get to a 4.11+ gear to balance the tall 6th in the T56.

The TCM shouldn't be a problem because the engine is LS1.

Sounds like you want a gear swap and not a new diff, correct?

Check the usual gear vendors, richmonds, etc.. for gears.

What I want is a final drive ratio change. Either a gear swap or replaced diff can achieve this, but 1 may be less expensive than the other. What I'm hoping to understand, is what might be available for replacement with other vehicles, or validation that a gear swap is the only real solution. I was also hoping for some confirmation of the Dana 44 heresay and maybe some experiences from someone who might have tried it...

Your final drive is the gear in the tranny. You want to change from your 3:08 gear to something higher and you need to contact a gear vendor and find out what is out there and what the cost is and trust me, you do NOT want 4.11 gears in a auto, not unless you plan on racing the car, because they will make city driving a pain. Gears and shims should run in the $300 - 500 range and installation is going to run $200- 1200.

If you go the gears route, make sure you get a shop that know what they are doing, otherwise you will wind up with scrap metal for a rearend. Do NOT do this yourself, unless you have done this and have all the dials and calipers, it is an easy job that you can screw up in a hurry with one wrong measurement.

The final drive ratio is a combination of final drive gear in the tranny [which is a manual in this case] the size of your tires, AND the differential gear which is 3.08 in this case. I totally agree with you too, I don't plan on tackling an install. But I would like to speak credibly about it.

Final drive meaning varies, depending on who you talk too, but I would ask this before you start changing anything.

1) what do you want out of the car, driver, race car , redlight warrior or a mix?

2) Is the tranny a manual or auto, need to consider TC for autos.

3) where does the engine live, meaning is it designed to run lowend, mid range or top end RPM range, this will effect the gears you put in the car.

4) what size tires are you going to run, this also effects the final drive as you put it.

Do not just throw gears on the car, you could windup making the car slower with the wrong setup. Trust me, I raced for years and I beat more people w/500+ hp and 4.11 gears, with my 375hp and 3.55's and all because they built a low or mid range engine and a rearend designed for a high revving engine.

Good q's and I appreciate your desire to help.
1) redlight warrior 2) manual t56 6spd 0.5 6th gear. 3) ls1 with hi rev cam 54-424-11 4)26.7" Thanks.

I have a T56 on my XK8 with a .62 final drive, I will be fitting a Quaife LSD with a custom made crown wheel and pinion giving me a 4.09 ratio

I haven't had the crown wheel made yet and would also be interested if a Dana 44 would fit, will save me a fair few $$

For a manual and 4.11's, all I can say is, I hope you like to shift.

Sounds like you would be better off with 3.74 to 3.89, you would be much happier, if you can find that kind of gearing anymore.

What year LS1?
Do you have the early 97-99 or the later, the 00 and up have higher redlines and are pretty much bullit proof.

That said, I will tell you that for a redlight warrior, traction is key and get heavy duty ujoints and enjoy your ride.

Also, look around the internet, there are a few good sights that have gear calculators and get on ls1.com or lt1ls1.com, they will probably be able to help you somemore.

Of course i like to shift.. that's why I put in a manual.
I had already done the calcs..that's why I wound up with a 4.11.
The Calc says current 6th gear is at 60mph at 1157 rpm.
With a 4.11 it'd be at 1552. Not as significant as I expected.... but mostly because the special 6th gear.

It's a 2002 Ls1.

Do you have the measurements for the wheel diameter and such? I bet we can compare to Dana parts to verify the assumption.

I did have a XK diff in bits some where, I will try and dig it out and have a measure, what I can tell you (if I remember correctly) the XK wheel was some what larger than the XJ, as the casings were a similar size I thought I might be lucky and so will be the pinion...... alas not

Andrezbin, do you have pics of your swap anywhere?

By the way, as a previous owner of a 98 SS with a T56 I would agree that a 4.10 might be a bit too much.

If I remember correctly auto ls1's had 3.08's from factory. My 6 speed had 3.42's which were great for the street/highway. I drove a 3.73 which was in my opinion the best all around combo - great improvement, I like shifting and it was more "lively" in that aspect, and it was still manageable around town and performed well on the highway. I also drove a friend's z28 with 4.10's (or 4.11 was it?) to the dragstrip once, and it was much too short in my opinion, and the car felt like it suffered on the highway.

If it was an all out track car aimed at tight slow/medium speed tracks then 4.10's could work really well, and be a nice aggressive choice. For anything that includes street or highway I would go 3.73.

But in the end, do whatever you want to ;)

If you have an XK8 with a 4.0ltr engine you can purchase a diff assembly that is for the Mexican market, 3.27 ratio. The TCM is the same som it is a straight bolt in. This will be non pozi. You can also bolt in a 3.58 or 3.77 pozi diff as well, they will require a new front mounting plate. I can attest to this as I fitted all 3 at diffferent times to my car. If you are interested I can give the source for this. The earlier Dana diff internals will not fit inside the later case as that was what originally wanted to do. I have to say it is quite an increase in acceleration with the 3.77 fitted.

Ok .. how much is "too much"?

Does the 3.58 require a reprogram?

The only person that I know who can reprogram the TCM on an XKR-XJR is Eurotek Desugns. The price is app $2000.00. If you are going to change the diff go with the 3.77. I have had both & highly recomend the 3.77. The other upgrade is the Blue Top solenoids.

So what vehicles have the 3.77?

The 3.77 LSD was fitted to the 6 cyl XJR in some markets. If you contact Coventry West they will sell you a rebuilt diff.