Jaguar Egypt V12 diff & transmission advice
Discussion
Hi,
Looking for some advice re: diff ratio on my Etype V12 roadster manual. It has a 3.31 ratio which l find gives too high revs at speeds above 55 mph. Ideally I need to fit a 5 speed gearbox however l'm not yet ready (mentally as well as financially) for an engine out scenario. What are thoughts from those who have the same model and gone thru the same decision process think about my idea of swapping out the 3.31 diff for a 3.07 diff or even for a 2.88 diff ratio ? I would keep the original diff. Key question is which diff ratio would fit best with a 5 speed gearbox that l'll probably fit later in the future? ( I realize a lot depends on which type of 5 speed gearbox but l'm looking for general advice. Any new gearbox l fit would only be one that fits without cutting or welding - l prefer to keep things simple and to the original design as far as possible.)
Hope some experts or folks in the know can advise, thanks.
Meonstoke
Looking for some advice re: diff ratio on my Etype V12 roadster manual. It has a 3.31 ratio which l find gives too high revs at speeds above 55 mph. Ideally I need to fit a 5 speed gearbox however l'm not yet ready (mentally as well as financially) for an engine out scenario. What are thoughts from those who have the same model and gone thru the same decision process think about my idea of swapping out the 3.31 diff for a 3.07 diff or even for a 2.88 diff ratio ? I would keep the original diff. Key question is which diff ratio would fit best with a 5 speed gearbox that l'll probably fit later in the future? ( I realize a lot depends on which type of 5 speed gearbox but l'm looking for general advice. Any new gearbox l fit would only be one that fits without cutting or welding - l prefer to keep things simple and to the original design as far as possible.)
Hope some experts or folks in the know can advise, thanks.
Meonstoke
Edited by Meonstoke on Saturday 31st October 20:14
Assuming your wheel/tyres are somewhere near original size you'll get the following results.
3.31 diff 3000revs/min 72mph
3.07 diff 3000revs/min 77mph
2.88 diff 3000revs/min 83mph
A 3.31 diff with 5 speed and fifth gear ratio of 0.8 will give you 90 mph at 3000 revs/min.
Personally I wouldn't waste money on a diff change I'd save up and fit a five speed box. Even with a conservative top gear ratio of 0.8:1 you can see from the above you're getting a better result.
3.31 diff 3000revs/min 72mph
3.07 diff 3000revs/min 77mph
2.88 diff 3000revs/min 83mph
A 3.31 diff with 5 speed and fifth gear ratio of 0.8 will give you 90 mph at 3000 revs/min.
Personally I wouldn't waste money on a diff change I'd save up and fit a five speed box. Even with a conservative top gear ratio of 0.8:1 you can see from the above you're getting a better result.
I don't think you'd want to put the over drive box on the back of a V12 I think the torque would eat it.
I had one fitted into my XK150 when I had 4.2 engine installed. It didn't last long and the people I spoke to about replacing it sort of sucked through their teeth and said, well it could well just eat the next one too. My overdrive box was serviced and "uprated" before it was installed. I can't remember the name of the company but I'd read a few article in the usual rags and the club mags that had mentioned them as being the best place for sort an OD box. The same basic unit was used on a very wide range of cars and the XK engines were the largest to try using it.
I ended up going for a 5 speed box, but it someways I think I'd have prefered to have tried swapping the diff instead. But that is because I miss the Moss box which to me is part of the charm of driving a 50s sports car. The 5speed box is just too easy to use.
I had one fitted into my XK150 when I had 4.2 engine installed. It didn't last long and the people I spoke to about replacing it sort of sucked through their teeth and said, well it could well just eat the next one too. My overdrive box was serviced and "uprated" before it was installed. I can't remember the name of the company but I'd read a few article in the usual rags and the club mags that had mentioned them as being the best place for sort an OD box. The same basic unit was used on a very wide range of cars and the XK engines were the largest to try using it.
I ended up going for a 5 speed box, but it someways I think I'd have prefered to have tried swapping the diff instead. But that is because I miss the Moss box which to me is part of the charm of driving a 50s sports car. The 5speed box is just too easy to use.
a8hex said:
I don't think you'd want to put the over drive box on the back of a V12 I think the torque would eat it.
I had one fitted into my XK150 when I had 4.2 engine installed. It didn't last long and the people I spoke to about replacing it sort of sucked through their teeth and said, well it could well just eat the next one too. My overdrive box was serviced and "uprated" before it was installed. I can't remember the name of the company but I'd read a few article in the usual rags and the club mags that had mentioned them as being the best place for sort an OD box. The same basic unit was used on a very wide range of cars and the XK engines were the largest to try using it.
I ended up going for a 5 speed box, but it someways I think I'd have prefered to have tried swapping the diff instead. But that is because I miss the Moss box which to me is part of the charm of driving a 50s sports car. The 5speed box is just too easy to use.
I've kept the Moss box with overdrive on my XK140 Special. The engine produces 250 hp and I've never had a problem with the overdrive in 10k miles. It was built by the late ex works Jaguar gearbox guru Alan George to competition spec (whatever that is)I had one fitted into my XK150 when I had 4.2 engine installed. It didn't last long and the people I spoke to about replacing it sort of sucked through their teeth and said, well it could well just eat the next one too. My overdrive box was serviced and "uprated" before it was installed. I can't remember the name of the company but I'd read a few article in the usual rags and the club mags that had mentioned them as being the best place for sort an OD box. The same basic unit was used on a very wide range of cars and the XK engines were the largest to try using it.
I ended up going for a 5 speed box, but it someways I think I'd have prefered to have tried swapping the diff instead. But that is because I miss the Moss box which to me is part of the charm of driving a 50s sports car. The 5speed box is just too easy to use.
I agree, fitting an overdrive to a V12 is a non starter, but the V12 never had a Moss box and a five speed doesn't alter the character in the same way it would in an XK.
mph said:
a8hex said:
I don't think you'd want to put the over drive box on the back of a V12 I think the torque would eat it.
I had one fitted into my XK150 when I had 4.2 engine installed. It didn't last long and the people I spoke to about replacing it sort of sucked through their teeth and said, well it could well just eat the next one too. My overdrive box was serviced and "uprated" before it was installed. I can't remember the name of the company but I'd read a few article in the usual rags and the club mags that had mentioned them as being the best place for sort an OD box. The same basic unit was used on a very wide range of cars and the XK engines were the largest to try using it.
I ended up going for a 5 speed box, but it someways I think I'd have prefered to have tried swapping the diff instead. But that is because I miss the Moss box which to me is part of the charm of driving a 50s sports car. The 5speed box is just too easy to use.
I've kept the Moss box with overdrive on my XK140 Special. The engine produces 250 hp and I've never had a problem with the overdrive in 10k miles. It was built by the late ex works Jaguar gearbox guru Alan George to competition spec (whatever that is)I had one fitted into my XK150 when I had 4.2 engine installed. It didn't last long and the people I spoke to about replacing it sort of sucked through their teeth and said, well it could well just eat the next one too. My overdrive box was serviced and "uprated" before it was installed. I can't remember the name of the company but I'd read a few article in the usual rags and the club mags that had mentioned them as being the best place for sort an OD box. The same basic unit was used on a very wide range of cars and the XK engines were the largest to try using it.
I ended up going for a 5 speed box, but it someways I think I'd have prefered to have tried swapping the diff instead. But that is because I miss the Moss box which to me is part of the charm of driving a 50s sports car. The 5speed box is just too easy to use.
I agree, fitting an overdrive to a V12 is a non starter, but the V12 never had a Moss box and a five speed doesn't alter the character in the same way it would in an XK.
I have a customer with a V12 roadster fitted with a Borg Warner 5 speed. It's beyond doubt the nicest I've driven; compact, very quiet and perfect shift quality. Definitely the one to go for.
J
Shame you don't have the physical room to fit one as they really are having your cake and eating it. I can't comment on your previous suppliers of overdrives being fragile. However, Gearvendors are rated to 2000bhp and 25000lb gvw. I'm putting one behind an 8 litre V8 and don't expect that little motor to cause it any issues.
normalbloke said:
Shame you don't have the physical room to fit one as they really are having your cake and eating it. I can't comment on your previous suppliers of overdrives being fragile. However, Gearvendors are rated to 2000bhp and 25000lb gvw. I'm putting one behind an 8 litre V8 and don't expect that little motor to cause it any issues.
Jaguar used the Laycock de Normanville overdrive, Wiki says that Gearvendors bought out the rights to the Laycock overdrives, but this one you mention seems a very different beasty. The Laycock de Normanville box was used in most British sports (& sporting) cars of the era from little MGs upto the Jaguar Mk10. On some of the Triumphs overdrive was available on 2nd, 3rd & 4th. On the Jaguars it was only available in 4th, so they must have known they were on the edge torque wise. It wasn't available on the E-Type, but was on the 4.2 MkX and the 420. So it did see service with the 4.2 engine.jith said:
Morning chaps. You can't fit an overdrive 'box to an E type because there is no room. The tunnel is too small. The other problem is that it won't last long in a V12 because of the torque.
I have a customer with a V12 roadster fitted with a Borg Warner 5 speed. It's beyond doubt the nicest I've driven; compact, very quiet and perfect shift quality. Definitely the one to go for.
J
Thanks JITH, MPH for your advice.I have a customer with a V12 roadster fitted with a Borg Warner 5 speed. It's beyond doubt the nicest I've driven; compact, very quiet and perfect shift quality. Definitely the one to go for.
J
With the getrag 5 speed mentioned is that also using a 3.31 diff? Or would a 3.07 or 2.88 ratio give a better / worse set of ratios to the character of the car which is effectively a boulevard cruiser? My excuses for being a dummy on this topic.
Using the numbers MPH gave above options with the 5speed box would be
axle ratio 3.31 3000RPM gives 90MPH
axle ratio 3.07 3000RPM gives 97MPH
axle ratio 2.88 3000RPM gives 103.5MPH
Aiming for 55MPH
axle ratio 3.31 1833RPM gives 55MPH
axle ratio 3.07 1700RPM gives 55MPH
axle ratio 2.88 1600RPM gives 55MPH
I'm not sure what you think of as being better, that is really rather subjective.
axle ratio 3.31 3000RPM gives 90MPH
axle ratio 3.07 3000RPM gives 97MPH
axle ratio 2.88 3000RPM gives 103.5MPH
Aiming for 55MPH
axle ratio 3.31 1833RPM gives 55MPH
axle ratio 3.07 1700RPM gives 55MPH
axle ratio 2.88 1600RPM gives 55MPH
I'm not sure what you think of as being better, that is really rather subjective.
a8hex said:
Using the numbers MPH gave above options with the 5speed box would be
axle ratio 3.31 3000RPM gives 90MPH
axle ratio 3.07 3000RPM gives 97MPH
axle ratio 2.88 3000RPM gives 103.5MPH
Aiming for 55MPH
axle ratio 3.31 1833RPM gives 55MPH
axle ratio 3.07 1700RPM gives 55MPH
axle ratio 2.88 1600RPM gives 55MPH
I'm not sure what you think of as being better, that is really rather subjective.
Thanks for the figures. I would think that a 2.88 diff with a 5 speed will give the most relaxed cruising speed on the motorway and should be still pleasant enough on winding B roads for the lower 4 gears. Hence, my original thought of changing from the current 3.31 diff to a 2.88 ratio; and enjoy that initially. And if its still not sufficient, then I still have the option of swapping out the 4 speed to a 5 speed manual getrag. (I guess a compromise could be to select a 3.07 diff to keep to the more sporting nature of an etype - and this diff ratio would still go well with a 5 speed. ) Hence, I see no obvious reason to want to marry a 3.31 diff with a 5 speed manual gearbox - or am I missing something in my way of thinking / approach?axle ratio 3.31 3000RPM gives 90MPH
axle ratio 3.07 3000RPM gives 97MPH
axle ratio 2.88 3000RPM gives 103.5MPH
Aiming for 55MPH
axle ratio 3.31 1833RPM gives 55MPH
axle ratio 3.07 1700RPM gives 55MPH
axle ratio 2.88 1600RPM gives 55MPH
I'm not sure what you think of as being better, that is really rather subjective.
As per my previous post I would keep the 3.31 diff and fit a five speed. Whatever top gear ratio the gearbox has, your cruising revs will be lower than a 2.88 diff with a four speed box.
In my opinion a 2.88 diff and five speed will be a step too far, whereas a 2.88 diff and four speed is a compromise. You won't get the ultimate relaxed cruising and you'll also lose some of the acceleration.
If anyone is interested I made up a calculator which allows for the input of wheel/tyre size, gearbox and diff ratios so that various options can be compared and the speed at any revs is shown.
PM with your email for a copy.
In my opinion a 2.88 diff and five speed will be a step too far, whereas a 2.88 diff and four speed is a compromise. You won't get the ultimate relaxed cruising and you'll also lose some of the acceleration.
If anyone is interested I made up a calculator which allows for the input of wheel/tyre size, gearbox and diff ratios so that various options can be compared and the speed at any revs is shown.
PM with your email for a copy.
I think that the OP needs to get himself on to the E Type club forum. Plenty of info on diff ratios and 5 speed or overdrive boxes.
The v12 e type uses the long wheelbase platform so the O/D box can be fitted without structural alterations.
The overdrive box has been fitted to the V12 by others successfully.
A search on the forum will reveal much factual information on this by those who have done it.
The v12 e type uses the long wheelbase platform so the O/D box can be fitted without structural alterations.
The overdrive box has been fitted to the V12 by others successfully.
A search on the forum will reveal much factual information on this by those who have done it.
tiggerjaguar said:
I think that the OP needs to get himself on to the E Type club forum. Plenty of info on diff ratios and 5 speed or overdrive boxes.
The v12 e type uses the long wheelbase platform so the O/D box can be fitted without structural alterations.
The overdrive box has been fitted to the V12 by others successfully.
A search on the forum will reveal much factual information on this by those who have done it.
I suppose it depends on how you term structural alterations. I have tried it and it won't go in without altering the tunnel. What is beyond argument is that the Laycock overdrive was absolutely not designed to take the torque of the V12. In fact it only just handled the late 4.2 engines. When I did the police cars we actually disconnected the overdrive to stop it being used as they failed regularly when being driven hard.The v12 e type uses the long wheelbase platform so the O/D box can be fitted without structural alterations.
The overdrive box has been fitted to the V12 by others successfully.
A search on the forum will reveal much factual information on this by those who have done it.
If you fit one in a V12 that has an enthusiastic driver it will almost certainly fail.
The other thing about this is, why would you bother when you can fit the BW 5 speed and make the car so driveable and considerably lighter?
J
jith said:
I suppose it depends on how you term structural alterations. I have tried it and it won't go in without altering the tunnel. What is beyond argument is that the Laycock overdrive was absolutely not designed to take the torque of the V12. In fact it only just handled the late 4.2 engines. When I did the police cars we actually disconnected the overdrive to stop it being used as they failed regularly when being driven hard.
If you fit one in a V12 that has an enthusiastic driver it will almost certainly fail.
The other thing about this is, why would you bother when you can fit the BW 5 speed and make the car so driveable and considerably lighter?
J
Hi JITH,If you fit one in a V12 that has an enthusiastic driver it will almost certainly fail.
The other thing about this is, why would you bother when you can fit the BW 5 speed and make the car so driveable and considerably lighter?
J
Interestingly the garage mentioned in the Etype UK forum mentioned by MPH in this thread also recommend the BW/Tremec T5 gear inc bell housing (over the long Getrag which are recon units). M&C Wilkinson advise a 2.88 diff ratio would fit best overall with the T5 gearbox; being able to make use of a top gear ratio of 0.8. Using a 3.31 diff ratio would also work but can then can only make use of a top ratio of 0.63). This was their advice, go for the 2.88 diff if possible - which sounds sensible, and fits with my original thinking. (They also advised against the overdrive option - over time, probably not consistently reliable enough.)
Anyone out there making use of BW/ T5 gearbox on a V12 roadster? Be good to get some feedback on their experience and on which diff ratio used.
Meonstoke said:
M&C Wilkinson advise a 2.88 diff ratio would fit best overall with the T5 gearbox; being able to make use of a top gear ratio of 0.8. Using a 3.31 diff ratio would also work but can then can only make use of a top ratio of 0.63). This was their advice, go for the 2.88 diff if possible - which sounds sensible, and fits with my original thinking. (They also advised against the overdrive option - over time, probably not consistently reliable enough.)
I really can't see where they're coming from. A 2.88 diff and a 0.8 top gear will give you a theoretical 190mph at 5500 revs ! Far too high geared in my opinion.A 0.8 top gear and a 3.31 diff is fine. I had similar ratios on my own V12 E Type. Theoretical 165 mph at 5500 revs. More than high geared enough I would think.
It's you car and your decision but I feel you'll be wasting money with a diff and gearbox change.
The 0.63 top gear ratio does give rather a large gap between fourth and fifth gears. I had a 4.2 with that gearbox and really didn't like it.
Jaguar specialists other than MCW are also available
Gassing Station | Jaguar | Top of Page | What's New | My Stuff