[E-Type] V12 Auto and 2.88 Diff


(Angus Moss) #1

Has anyone got views on fitting a 2.88 diff to an auto V12?
Will it have any negative effect on performance?

Car is currently running with a 3.30.–
65 OTS 1E11497 www.mossjaguar.com
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(Norman LUTZ) #2

In reply to a message from Angus Moss sent Wed 19 Mar 2014:

Yes it will reduce performance fractionally but it makes it
the same as an XJS HE–
The original message included these comments:

Will it have any negative effect on performance?


850225/679,1E21003,2W2001BW,JNAEY3AC100218,SAJNV4841KC156072
ROSANNA, Australia
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(Angus Moss) #3

In reply to a message from Norman LUTZ sent Wed 19 Mar 2014:

Thanks Norman. He’s looking for a long distance cruiser so
the 2.88 seemed like a good option.–
65 OTS 1E11497 www.mossjaguar.com
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(david collins) #4

In reply to a message from Angus Moss sent Wed 19 Mar 2014:

don’t forget you have to change the speedometer if you
change the rear differential ratio. 2.88 diff gets you off
the line slower but cuts revs at high speed.

dave collins.–
david collins
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(MarekH) #5

In reply to a message from david collins sent Wed 19 Mar 2014:

Dear Angus,

My car was running a 2.88 differential for a long time before I put
a manual gearbox in. Aside from running lower rpm at cruising
speeds, it appeared to make no material difference to the car.

kind regards
Marek–
v12 E-type running MS3/3X sequential lpg and petrol
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(Philip Lochner) #6

I have now fitted a 2.88 to my S3 (auto)

Its important to understand that my car was fitted with a 3.31 by some PO. If my car had the original 3.07, I would not have bothered. But running 3300rpm @ 120km/h (our speed limit) seemed so wasteful.

I removed the IRS (alone) in two hours - having done this before. Building the 2.88 into the IRS and installing the IRS back into the car took the rest of the day. Had to connect/bleed brakes (incl handbrake), connect propshaft, and install exhaust the following day.

There were no “showstoppers”. Calipers and discs went straight on, propshaft mounted fine.

Now she does 2850rpm (indicated tacho) at GPS 120km/h (115km/h on speedo). My car is fitted with 215/70/15 tyres. According to Ashcroft she should be doing 2686rpm at GPS 120km/h. Perhaps the tacho is not 100% accurate.

Very pleased with the end result. Standing start only slightly blunted but now she will do 100km/h in 1st. I will compare odo readings against GPS odo to be able to calculate exact fuel consumption.


(PeterCrespin) #7

Since the V12 has a red line 1000 rpm higher than the 4.2, and is sweeter than the old long-stroke six at high rpm, I never think of low gearing as being a problem for a V12. 3300 is just getting ready to rock and roll, with instant hard acceleration that you don’t normally get from a 5.3 until it has some revs. As for the effect on fuel consumption, who really notices the difference between 12 mpg and 14 mpg?


(Philip Lochner) #8

I do.

This car mostly does open road with 99.99% steady cruising and 0.01% overtaking (which is mostly done in top gear anyway). It gives me huge pleasure to get the best fuel consumption possible out of this 46 year old car (that still runs with the youngsters) and if those figures compete with modern cars of similar engine size - all the better.

My Jensen Interceptor with a high compression 7.2L EFI’ed engine with a GM 4L60e gearbox (which offers a 0.7 4th) has shown me the value of using torque rather than HP. The Jag V12 is also a potent torque generator (it just does not sound like its producing all this torque between idle and 2000rpm) and I would much rather use the torque it offers between idle and 2000rpm than whatever HP it offers above 3000rpm.

Wish the E also had the 4L60e… Imagine cruising at 120km/h in the E doing just under 2000rpm. Bliss.