I have just finished the diff change from a 3.08 to a 2.28 from a turbo R,it was a little harder than I expected as I had to get the shaft cut & joined.
The car in far better,@ 12 mph on the speedo it is doing 16 as it changes into second,at 20/22 in second it is doing 30 as it changes gear into 3rd.On the motorway @ 45 on the speedo it is doing 60 mph.
The car is quietly,less revs,less wear,less oil,less fuel ( it should be 25 to 30% better on fuel costs) I use LPG @ 3.18 € a gallon @ 11.5/11.8 mpg,I expect 15/17 on lpg with this diff which should be equal to 30 mpg € for € on petrol.
I will post it as it happens.
I expect to get my money back in fuel saving in 4/6 months as I drive it 300/400 hundred miles a week
Kevin Deasy
Sorry I never answered your question (24/3/16)
The car went much better,as I drove it on motorways
@ 100/130 KLMS on a daily basis it was running @3000/3500 rpm
After the diff change it was @ 2200/3000 rpm.A quieter car,no vibrating,you could only hear
The wind at 130.it went like a rocket.
And doing 11.5 to 13 mpg on LPG (23 to 26) I have changed the car for a Spirit
Also on LPG.I won't change the diff as I only do 100/150 miles a week now
I live in Wicklow town & don't travel to Dublin every day as I retired in June.
Kevin
i have a V12 5.3 it had a 2.88 Diff that when Starting from a stand still it drank fuel faster than me and a pint so i put a 3.54 in which was fantastic but no top end so i then drooped a 4 speed in and know i have the best of both worlds
Depending on its age yours will be a 2.28 or a 2.69.
If it is a 2.28 & you want more acceleration the 2.69 should be a direct replacement ( I think) and be easy to do.
If it is the 3 speed box you could consider a 4 speed.
I intend to look at doing this to the next mark 2 Spirit or getting an o/d box built.
Hi Kevin, I'm averaging 15-16 mpg on premium gas now. Was only getting 12-13 when I first got her, but several bottles of fuel injection cleaner have helped. As well as an ignition tune up.
Mark
BTW, I have a heavy foot
it was doing 14/16 it is know doing 22/24 with a hard foot
yes it runs very well the gearbox is a GM4l80E it is run on a Optishift ECU http://www.usshift.com/newname.shtml the same gearbox as the late RR&B's
as it needs to control the box and is fully programmable so can be fast road or cruising
I'm guessing that with the renaming to US Shift that what used to be the OptiShift has now become the Quick 4 with the expansion of their line. [Unless it was the Quick 1, which is no longer made].
what i did was get rid of Lucas ignition as i love the car and i have owned it from 1990 i wanted to make it more user friendly
so out with the 5.3 3 speed in went 6.L 4 speed out went all the electrics and a stand alone Emerald stand alone ecu and the Q.4 out went the inboard rear brakes and in went the later outboard also all suspension is fully adjustable
also all sensors are Bosch so can be replaced any where in the world
so she is a happy Jag and both ECU's are programmable
Bentleyman22, there is a guy in Texas that sells an adapter to install a GM 700R4 to the Jag V12 block. Very little electronics to deal with. I had an XJS and enjoyed it, but I would have LOVED the 6.0!
Yes i could have done that as there is a Jag man in the uk that has the plate but as i had the complete front end out for stove enamelling it was silly not to drop the 6 in but as i have the E box in the Bentley and love it i went this way
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