Damn Jag... You are the Man!!!

I'm going to leave things as is,,, based on what you said... Thank you, Much! Except on occasion, I am more the Sunday driver. I assumed (and you know what they say about that) that increasing the ratio (and again I assumed) between drive shaft rotations and diff rotations - if that's even the relationship - that most of what you said would be the opposite... That the engine would work less, that the revs would be lower, and such - but it would cruise smooooother and rev slower on say,,, the highway I have a lot to learn,,, starting basically from the beginning...

Thank you. You prevented me (for now) from getting onto a road I thought I knew,,, but DID not... It's all good. Still all eyes and ears. Peace

 

What the ratio refers to is the number of turns the driveshaft ( and thus engine) do compared to the number of revolutions the tire does. Thus for a 2.88 ratio, the engine ( when in top gear on the transmission) will do 2.88 turns for every turn of the tire. Changing to a numerically higher number, like 3.54 increases the engine revs compared to the tire revs.

In terms of the engine "working" that will play into where the torque peak is on the engine. Ideally, the torque peak is where the cruising speed revs coincide, it makes the car feel more responsive. Although people often talk of horsepower, torque is more important to how "powerful" a car feels. Working within their constraints, the Jaguar engineers were an incredibly talented group and knew what they were doing.

 

i use a 3.73 rear gear, with a 700R4 overdrive ,, final ratio comes out to 2.60, plenty of accel. and great highway cruise, best of both worlds!!
ron

 

Just swapped my 2.88 out last week to the 3.54 LSD from a 3.6L XJS.

Very noticeable difference in acceleration. I am very happy with the result.

Took 20 hours of mechanic labour and it cost me around NZD$1600.00 which included new discs and ceramic brake pads. (price does not include the new differential)

Was well worth the effort albeit a little more hungry on fuel, but who cares when you have a V12!

Craig

 

JJJ, there are 700R4 swaps that are very effective.

I have a 4L60e with a 3.58 diff and out of the blocks is a vast improvement and hwy RPM is even less than 2.88 with TH400 my car is about 2000rpm at 100km/h

In the USA there are kits to do this swap and it is very worthwhile..

There are at least 2 Targa XJS race cars around Oz running low diffs (4.09) with the 2.88 centre and a machined spacer, it works if done correctly.

 

Are there any links to these swap kits?