HELP- Confused about diff ratios
Discussion
I'm looking to replace the DIFF in my 280i wedge.
I think it SHOULD have a 3.07:1 in it....
I believe that the Jaguars (that TVR borrowed the diff from) have 3.07 and 3.54 ratios.
It would appear the diff fitted to my wedge is a 3.31? The speedo is "slightly" out (on the good side i.e. if i'm on the limit with the speedo its under the limit in reality).
Anyone albe to shed any more light? Maybe know where I can get a diff at reasonable money?
Thanks in advance
Norman
I think it SHOULD have a 3.07:1 in it....
I believe that the Jaguars (that TVR borrowed the diff from) have 3.07 and 3.54 ratios.
It would appear the diff fitted to my wedge is a 3.31? The speedo is "slightly" out (on the good side i.e. if i'm on the limit with the speedo its under the limit in reality).
Anyone albe to shed any more light? Maybe know where I can get a diff at reasonable money?
Thanks in advance
Norman
Edited by wedgeinald on Thursday 11th September 14:57
The reason I ask is because a 5 speed box has 5th as an overdrive gear ..
4th is usually 1:00 and 5th around 0.75 to 1.
Now with the diff ratio - 3.54 would give a very low top speed in 4th, 3.07 ration would give a high top speed but would severly blunt acceleration in the 4 gears.. so the 3.31 ration probably gives you the best compramise.
Hope that helps.
4th is usually 1:00 and 5th around 0.75 to 1.
Now with the diff ratio - 3.54 would give a very low top speed in 4th, 3.07 ration would give a high top speed but would severly blunt acceleration in the 4 gears.. so the 3.31 ration probably gives you the best compramise.
Hope that helps.
Edited by rev-erend on Thursday 11th September 16:46
Thanks Rev I think the speedo was setup (roughly?) for a 3.07.
With its current diff the speedo over reads by quite a bit (and I assume with a 3.54 it would be worse?)
I have two options
1) try and get a correct diff (with the decrease in acceleration - will I REALLY notice?) and have a more accurate speedo and better top end (like i need that??).
2) Fit what I can find as long as it fits/works and either get the speedo re-calibrated or allow for the over-read (don't want to be on a motorway doing under 60 just because my speedo says i'm doing 70??) I have a satnav so can get a gauge of how far out the speedo is from that.
I have PM'd about the diff as well....
Norman
With its current diff the speedo over reads by quite a bit (and I assume with a 3.54 it would be worse?)
I have two options
1) try and get a correct diff (with the decrease in acceleration - will I REALLY notice?) and have a more accurate speedo and better top end (like i need that??).
2) Fit what I can find as long as it fits/works and either get the speedo re-calibrated or allow for the over-read (don't want to be on a motorway doing under 60 just because my speedo says i'm doing 70??) I have a satnav so can get a gauge of how far out the speedo is from that.
I have PM'd about the diff as well....
Norman
2.88 - Some V12s ...rare.
3.07 - 4.2 litre XJ6 auto's
3.31 - also 4.2 litre XJ6 autos
3.54 - all 3.4 litre cars and 4.2 litre manuals.
I'm sure that my first XJ6, a Series one 2.8 Auto came with a LOWER diff...say 3.9:1
They must be pretty thin on the ground though.
You can also raise or lower the final drive ratio by fitting larger or smaller diameter wheel/tyre combo on the back.
Your diff should (in theory) have a metal tag on it, giving the ratio.
3.07 - 4.2 litre XJ6 auto's
3.31 - also 4.2 litre XJ6 autos
3.54 - all 3.4 litre cars and 4.2 litre manuals.
I'm sure that my first XJ6, a Series one 2.8 Auto came with a LOWER diff...say 3.9:1
They must be pretty thin on the ground though.
You can also raise or lower the final drive ratio by fitting larger or smaller diameter wheel/tyre combo on the back.
Your diff should (in theory) have a metal tag on it, giving the ratio.
...could on my 280.My V12 Jag used to do 90+ in second....found that out on the track at Brands Hatch.
XJ12C ~90mph (held down in) 2nd gear ~5000rpm coming off the last corner accelerating onto the main straight....great fun...still have the video somewhere.
Not pushed the TVR that hard yet...but it certainly goes well. I'm very happy with the Wedge.
XJ12C ~90mph (held down in) 2nd gear ~5000rpm coming off the last corner accelerating onto the main straight....great fun...still have the video somewhere.
Not pushed the TVR that hard yet...but it certainly goes well. I'm very happy with the Wedge.
I think 3.31 is the best ratio for your car / engine and gearbox.
a 3.07 will dull acceleration to give you a theoretically higher top end. does your car have enough power to attain max revs with a taller ratio though?
3.31 is a very popular diff ratio.
Going up an inch in tyres will give you a more relaxed top end. switching to a 5sp overdrive will lower your revs slightly
depends what you want though. I would only go to a 3.07 if you were commuting on the motorway to work everyday over long distances.
N.
a 3.07 will dull acceleration to give you a theoretically higher top end. does your car have enough power to attain max revs with a taller ratio though?
3.31 is a very popular diff ratio.
Going up an inch in tyres will give you a more relaxed top end. switching to a 5sp overdrive will lower your revs slightly
depends what you want though. I would only go to a 3.07 if you were commuting on the motorway to work everyday over long distances.
N.
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