TWR XJS engine and gearbox from 84 to 88?

[alastaircm]

As per the title, I'm looking to make contact with anyone who has experience/knowledge of the engine modifications and/or gearbox fitted by TWR Jaguarsport to their XJS offering between 1984 and mid 1988 (the conversion TWR offered before they launched the XJR-S as part of the Jaguar Sport joint venture).

I'm looking at the prospect of restoring a car that was converted in mid 87 and fitted with the ZF manual gearbox and 6.1L V12 engine conversion with all of the other TWR options. I already have another TWR XJS that has all the TWR options except the engine and gearbox, so am fairly good on all the other special bits.

I'm looking for any additional info I can get about what I'm likely to come across before I start taking anything apart or making any decisions. I already have all the background info available from magazine articles, brochures and press releases etc. Would also love to make contact with anyone who may have been involved with the conversion at TWR and I can provide further details directly about the car, ownership and registration.

[v8250]

Why not put a call out into Jaguar circles / Jaguar Heritage / XJS Club? There are a good number of knowledgeable folk out there who used to work at TWR and the Jaguar/TWR joint venture. A quick google search can bring up a host of names and contacts.

...and this sounds rather good...https://www.youtube.com/watch?v=UhXLysNl-wE#t=64

Edited by v8250 on Thursday 13th November 16:04

[XJ Flyer]

I think there is a difference between the engine upgrade that produced the capacity increase in that version as opposed to the later 6.0 L XJRS.The former was based on a bigger diameter liner/bore/piston kit whereas the latter was based on a longer throw crank/stroke.I'm also guessing it would be based on the earlier rear main rope type seal as opposed to the later type.If it needs an engine rebuild it would probably be better to obtain a later type 6.0 litre of either Jaguar or TWR type and then put the bigger liner kit in that which is available from Rob Beere.

It would then be the best of both worlds in the form of a big bore longer stroke 6.8 L as opposed to just a large bore 6.1 or long stroke 6.0 litre.Which is what I was planning to do with my 6.0 long stroke TWR engine if only my budget had allowed it.

[Finlandese]

Are you sure it has a ZF-transmission? I was under the impression that the TWR´s had Getrag transmissions.

[alastaircm]

Thanks for the responses so far.

The Group A racers used a getrag box. The manual road cars used a custom built ZF box bult in very small numbers that was I believe also only used in small numbers in the Alpina B7S. I've read it was originally designed for an abandoned BMW V12 project. I'm told the manual option was not very popular any very few of the manual cars are said to exist.

The earlier TWR engine is different from the one used in the XJR-S, it is said to be a lot more powerful for a start if you believe the quoted figures. Brochures describe it as being stroked with a longer throw rather than a larger bore, but also with modified pistons (I've been told from Cosworth with left and right handed pistons) and also reprofiled/modified valves. That's about all I know. Hopefully it won't need a rebuild but if it does it would be to original specification to preserve the car's originality.

Yes I am trying other avenues including the XJS Club but thought this forum would also be a good place to look given the range of membership and assembled wisdom!

[XJ Flyer]

alastaircm said:

Thanks for the responses so far.

The Group A racers used a getrag box. The manual road cars used a custom built ZF box bult in very small numbers that was I believe also only used in small numbers in the Alpina B7S. I've read it was originally designed for an abandoned BMW V12 project. I'm told the manual option was not very popular any very few of the manual cars are said to exist.

The earlier TWR engine is different from the one used in the XJR-S, it is said to be a lot more powerful for a start if you believe the quoted figures. Brochures describe it as being stroked with a longer throw rather than a larger bore, but also with modified pistons (I've been told from Cosworth with left and right handed pistons) and also reprofiled/modified valves. That's about all I know. Hopefully it won't need a rebuild but if it does it would be to original specification to preserve the car's originality.

Yes I am trying other avenues including the XJS Club but thought this forum would also be a good place to look given the range of membership and assembled wisdom!

I'm not sure which way round you've described the big bore v long stroke TWR engines there.But as I said the XJRS engine is certainly just a long stroke ( 78 mm ) conversion.Which Jaguar then carried over with its own 6.0 litre versions of the V12.As for ZF v Getrag as far as I know the ZF was certainly the box of choice in the case of TWR manual conversions both race or road spec.

The problem being that the ZF is a direct top type while the Getrag is overdrive.In which case the ZF provided no higher speed running advantages over the old Jaguar four speed it just provided an arguably pointless low first and relatively closer ratios.In the case of the Getrag it allows/needs a lower final drive ratio ( 3.07 etc ) than the 2.88 in the 80's cars while still providing a higher top gear all of which offers arguably more advantages than the ZF.Although some say the torque capacity of the Getrag is marginal in the case of the V12.The combination of that and saving the need to change the final drive might have been what TWR was basing its choice on.However there are plenty of examples both road or race which show that the Getrag is more than strong enough for the job.Realistically in the case of the XJS or series saloons it is better to trade originality for optimum performance potential by combining the best available component options within the budget which is really what TWR was doing anyway.

In which case using the big bore conversion on the long stroke engine together with the Getrag box and a 3.07 final drive is probably about as good as it gets and would be well worth trading TWR originality for.

[XJ13]

XJ Flyer said:

the Getrag box and a 3.07 final drive is probably about as good as it gets and would be well worth trading TWR originality for.

Alastair - are you sure the manual road cars used ZF - I understood that TWR originally fitted the Getrag 265 to their XJS? Could the ZF box have been added by a later owner? If this is the case, you wouldn't be "trading TWR originality" by going for Getrag?

I do look forward to reading more about your project as it develops - keep us posted!

[alastaircm]

XJ13 said:

Alastair - are you sure the manual road cars used ZF - I understood that TWR originally fitted the Getrag 265 to their XJS? Could the ZF box have been added by a later owner? If this is the case, you wouldn't be "trading TWR originality" by going for Getrag?

I do look forward to reading more about your project as it develops - keep us posted!

The original press release from the 1984 Brussels motor show specifies it as a ZF gearbox. Every specification price list between 1984 and 1988 also specifies a ZF gearbox. If a customer was willing to pay for it I'm sure they would have fitted whatever you want, but the ZF was always stated as the standard option.

I am sure there would be lots of options to improve the performance but the object of the exercise is to keep the car original. I have another TWR with a standard v12 and automatic box which would be the better choice for any bespoke engine and gearbox modifications.

Not sure about a comparison to the original 4 speed box or the getrag, as the ZF 5th gear is a 0.83 overdrive gear.

[XJ Flyer]

alastaircm said:

The original press release from the 1984 Brussels motor show specifies it as a ZF gearbox. Every specification price list between 1984 and 1988 also specifies a ZF gearbox. If a customer was willing to pay for it I'm sure they would have fitted whatever you want, but the ZF was always stated as the standard option.

Not sure about a comparison to the original 4 speed box or the getrag, as the ZF 5th gear is a 0.83 overdrive gear.

I'd agree that the ZF box is the usually accepted option chosen by TWR in the case of its manual conversions.But an overdrive ZF is a surprise.Although,at least in the case of the ZF box,that is all only based on second hand information not first hand.

IE as far as I know from second hand sources we are talking about the usual dog leg shift pattern ZF with the out left and back first position ? as opposed to the Getrag's out right and forward top position ?.

Which usually denotes/identifies a direct top ZF v overdrive Getrag.

[alastaircm]

XJ Flyer said:

I'd agree that the ZF box is the usually accepted option chosen by TWR in the case of its manual conversions.But an overdrive ZF is a surprise.Although,at least in the case of the ZF box,that is all only based on second hand information not first hand.

IE as far as I know from second hand sources we are talking about the usual dog leg shift pattern ZF with the out left and back first position ? as opposed to the Getrag's out right and forward top position ?.

Which usually denotes/identifies a direct top ZF v overdrive Getrag.

Inetersting, I've never seen anything to suggest the gearbox had other than an overdrive 5th gear. The shift pattern is not as you describe it. Out left and up is reverse, there is no out left and down. 1 to 4 is in a standard H pattern in the middle. 5th is out right and up. As below (I had to use the dots to get it to show correctly but 2 and 4 should line up with 1 and 3):

R 1 3 5
|_|_|_|
..| |
..2 4

The gear positions on the shifter in the car match exactly the ones shown in the TWR press pack from 1984. Perhaps you are thinking of a different ZF box?

Every piece of TWR documentation they released about the car, of which I have all the originals, says its a ZF box with an overdrive 5th gear and gives the gear ratios. Every contemporary magazine article reviewing the TWR car says its a ZF box and some mention the overdrive 5th gear.

Edited by alastaircm on Friday 14th November 23:18

[XJ Flyer]

alastaircm said:

XJ Flyer said:

I'd agree that the ZF box is the usually accepted option chosen by TWR in the case of its manual conversions.But an overdrive ZF is a surprise.Although,at least in the case of the ZF box,that is all only based on second hand information not first hand.

IE as far as I know from second hand sources we are talking about the usual dog leg shift pattern ZF with the out left and back first position ? as opposed to the Getrag's out right and forward top position ?.

Which usually denotes/identifies a direct top ZF v overdrive Getrag.

Inetersting, I've never seen anything to suggest the gearbox had other than an overdrive 5th gear. The shift pattern is not as you describe it. Out left and up is reverse, there is no out left and down. 1 to 4 is in a standard H pattern in the middle. 5th is out right and up. As below (I had to use the dots to get it to show correctly but 2 and 4 should line up with 1 and 3):

R 1 3 5
|_|_|_|
..| |
..2 4

The gear positions on the shifter in the car match exactly the ones shown in the TWR press pack from 1984. Perhaps you are thinking of a different ZF box?

Every piece of TWR documentation they released about the car, of which I have all the originals, says its a ZF box with an overdrive 5th gear and gives the gear ratios. Every contemporary magazine article reviewing the TWR car says its a ZF box and some mention the overdrive 5th gear.

Edited by alastaircm on Friday 14th November 23:18

Thanks for that information.It would be interesting to find out exactly which ZF box that was which they used ?.Is it shown on any id plates attached to it ?.The information which I was going by was obviously based along the lines of the S5/31 series used in BMW's for example.

Having said that the shift pattern which you've posted there is certainly the same as the Getrag overdrive box as well assuming that's a ZF.The ratios might also help to identify exactly which ZF type they used.But certainly in the day ZF were usually associated with the direct top dog leg first spec as opposed to Getrag which was usually associated with overdrive types.So it wouldn't be surprising if that has created some confusion over the years between Getrag fitted cars v ZF ones in that the shift pattern and being overdrive was the same for both in this case. As opposed to the usual dog leg first and direct top in the case of most ZF's.

Edited by XJ Flyer on Saturday 15th November 00:15

[alastaircm]

XJ Flyer said:

Thanks for that information.It would be interesting to find out exactly which ZF box that was which they used ?.Is it shown on any id plates attached to it ?.The information which I was going by was obviously based along the lines of the S5/31 series used in BMW's for example.

Edited by XJ Flyer on Saturday 15th November 00:15

The transmission case has the identifier stamped into it, S5/40.

There is no information plate, I guess since these were custom made. I've been told that the internals were assembled into the case at Kidlington by TWR before being fitted to the car rather than being supplied as a complete unit, but was hoping someone could verify.

There is a little bit of info scattered around with some pictures, mostly on BMW forums with reference to the Alpina. It makes sense since TWR were a distributor for Alpina parts in the early 80s that they knew about this box. I think the initial order from TWR was for 50 units, not sure if they ever made further orders but there is second hand information that a lot of the boxes were not fitted as it was not a popular option.

[XJ Flyer]

alastaircm said:

XJ Flyer said:

Thanks for that information.It would be interesting to find out exactly which ZF box that was which they used ?.Is it shown on any id plates attached to it ?.The information which I was going by was obviously based along the lines of the S5/31 series used in BMW's for example.

Edited by XJ Flyer on Saturday 15th November 00:15

The transmission case has the identifier stamped into it, S5/40.

There is no information plate, I guess since these were custom made. I've been told that the internals were assembled into the case at Kidlington by TWR before being fitted to the car rather than being supplied as a complete unit, but was hoping someone could verify.

There is a little bit of info scattered around with some pictures, mostly on BMW forums with reference to the Alpina. It makes sense since TWR were a distributor for Alpina parts in the early 80s that they knew about this box. I think the initial order from TWR was for 50 units, not sure if they ever made further orders but there is second hand information that a lot of the boxes were not fitted as it was not a popular option.

Thanks for clarifying that.It seems obvious where at least some of the confusion of those who've erroneously thought that TWR used Getrag boxes might have originated from.IE in most respects,like shift pattern and overdrive not direct top format,the ZF used was very similar to,if not same as,the Getrag's format.

I can remember looking into the possibility of using a ZF option when I first did did my V12 manual conversion and I think I can remember ZF offering some custom ratio availability.But the cost and,the obviously erroneous, idea that ZF was all about the direct top and too low first format was the deal breaker in my case.That was even before getting to the question of overdrive v direct top option availability which at least would have made the ZF a more attractive choice than if it had been lumbered with only the direct top only format.

While the Getrag was available in large numbers new or used at relatively much lower prices together with a large affordable supply network for the other parts required like bell housings and clutch/clutch release systems.

As for TWR's conversions they were always at the more expensive end of the manufacturer sanctioned tuning sector.Which probably explains in large part the rarity of the TWR larger capacity and manual box modified cars.Not that the demand wasn't there.

In the case of those earlier TWR conversions it seems a fair bet that it is a bigger bore conversion of the earlier type 5.3 engine together with a very rare overdrive 5 speed ZF option.

As opposed to the long stroke 6.0 litre XJRS which probably would have been even more expensive if ordered with a TWR ZF manual conversion and any of those which have been converted to manual since would probably be likely have used an aftermarket Getrag box conversion on grounds of cost.

I can only assume that TWR went to all the trouble and expense of an obviously rare and specialised ZF option because of those arguable issues of the Getrag's marginal torque input capacity when fitted to the V12.

[alastaircm]

XJ Flyer said:

In the case of those earlier TWR conversions it seems a fair bet that it is a bigger bore conversion of the earlier type 5.3 engine together with a very rare overdrive 5 speed ZF option.

As opposed to the long stroke 6.0 litre XJRS which probably would have been even more expensive if ordered with a TWR ZF manual conversion and any of those which have been converted to manual since would probably be likely have used an aftermarket Getrag box conversion on grounds of cost.

If the engine is the same as the "test" version referred to at the end of Alan Scott's book then the higher capacity is through increasing the stroke alone. He quotes an 80mm crankshaft as being used to increase capacity to 6.1L. The chart he reproduces for the variations of that test engine seem to match the quoted characteristics for the early TWR 6.0L engine (may be different to the 6.1 engine?)of 380 BHP. Although publications also talk about valve re-profiling and a change in compression ratio which Alan Scott doesn't mention in his description of the various tests.

The 6.0L XJRS was a different engine with a 78.5mm crankshaft with lower BHP and peak torque figures than the earier TWR engine. Probably in part because the TWR exhaust modifcations were not carried over to the XJR-S although the larger air intakes were. It could not be ordered with the ZF box becuase Jaguar Sport never offered the range of earlier modifications for the XJR-S that TWR offered. Unless you could have paid them to do a special as a one off?

Hence you can see that some input from someone who worked on these early cars would probably clear all of this up in a few minutes. Either that or I start stripping the engine apart just to find out what is in there

Edited by alastaircm on Wednesday 19th November 13:24

[XJ Flyer]

alastaircm said:

XJ Flyer said:

In the case of those earlier TWR conversions it seems a fair bet that it is a bigger bore conversion of the earlier type 5.3 engine together with a very rare overdrive 5 speed ZF option.

As opposed to the long stroke 6.0 litre XJRS which probably would have been even more expensive if ordered with a TWR ZF manual conversion and any of those which have been converted to manual since would probably be likely have used an aftermarket Getrag box conversion on grounds of cost.

If the engine is the same as the "test" version referred to at the end of Alan Scott's book then the higher capacity is through increasing the stroke alone. He quotes an 80mm crankshaft as being used to increase capacity to 6.1L. The chart he reproduces for the variations of that test engine seem to match the quoted characteristics for the early TWR 6.0L engine (may be different to the 6.1 engine?)of 380 BHP. Although publications also talk about valve re-profiling and a change in compression ratio which Alan Scott doesn't mention in his description of the various tests.

The 6.0L XJRS was a different engine with a 78.5mm crankshaft with lower BHP and peak torque figures than the earier TWR engine. Probably in part because the TWR exhaust modifcations were not carried over to the XJR-S although the larger air intakes were. It could not be ordered with the ZF box becuase Jaguar Sport never offered the range of earlier modifications for the XJR-S that TWR offered. Unless you could have paid them to do a special as a one off?

Hence you can see that some input from someone who worked on these early cars would probably clear all of this up in a few minutes. Either that or I start stripping the engine apart just to find out what is in there

Edited by alastaircm on Wednesday 19th November 13:24

Assuming that the TWR 6.1 litre conversion was done by increasing the stroke that would certainly be an unusual bore/stroke combination for the V12.However that capacity increase is still available from the usual tuning suppliers in the form of a 96 mm bore conversion on the 5.3 which seems a coincidence.That type of conversion would ideally also really need pre HE heads to take advantage of the increased bore size by increasing the valve area.Which would explain a lower compression ratio and different valve sizes.

It might be possible/interesting to try to get a measurement of the piston travel between top dead centre and bottom dead centre using a depth type gauge through the spark plug hole.While I think pre HE heads can be identified by spark plug type.Assuming a 70 mm piston travel then that would at least answer the question as to wether it was a big bore conversion,or a long stroke one similar to the XJRS.

As for XJRS output figures the main problem was the worst of all worlds combination of the small valve HE type heads with the low pre HE type compression ratio used.Probably because of the issues of the relatively poor octane availability in unleaded fuel in the day as cats were being introduced.IE something like the problem of US spec V12's which were always hindered by their tuning for low quality US fuel and emissions regs.IE HE heads need massive compression ratios to work properly and provide a reasonable output and therefore high octane unleaded fuel which is available now but wasn't in the day.

However assuming it was a 6.1 long stroke conversion, together with an overdrive ZF box that might possibly be a nightmare to maintain in the long term if it ever needs any major bottom end engine or transmission parts.Because of their rarity.

In terms of availability and best all round performance as I've said I wouldn't be too worried about staying with TWR originality.At least in the case of anything major like engine or gearbox letting go and needing a rebuild.

If only I had the money I'd go for the ideal of adding a 96 mm bore conversion to the XJRS ( or Jaguar ) long stroke 6.0 taking it to 6.8 either with proper HE levels of compression ratio or pre HE big valve heads.In which case that would provide power outputs well into the 400 's,probably closer to 500,let alone 380,with less worries about parts availability.

Having said that the standard relatively low compression XJRS engine makes an easy 350 hp with a multiple throttle set up and straight through exhausts so long as its a pre cat requirement car.

[urquattroGus]

Trying to decide whether an XJRS or XJR-S is worth it over me modifying a very clean 5.3HE car with TWR Bodykit, Steeringwheel etc

Of course Ideally I'd love to find a car with the 6.1 pre jaguar sport TWR engine and a manual box already fitted.... But I should be so lucky!

I have found a clean 1986 car with TWR accessories/kit from new, but no engine or gearbox mods.

I wonder if fitting a manual box, different induction and exhaust will give me a freer revving 5.3 engine than the longer stroke 6.0 from the XJRS/XJR-S???

[skwdenyer]

Intrigued by the bore/stroke discussions, I found this:

http://www.jagweb.com/aj6eng/stretching.php

A 10 litre XJ-S sounds interesting

[lukeharding]

urquattroGus said:

Trying to decide whether an XJRS or XJR-S is worth it over me modifying a very clean 5.3HE car with TWR Bodykit, Steeringwheel etc

Of course Ideally I'd love to find a car with the 6.1 pre jaguar sport TWR engine and a manual box already fitted.... But I should be so lucky!

I have found a clean 1986 car with TWR accessories/kit from new, but no engine or gearbox mods.

I wonder if fitting a manual box, different induction and exhaust will give me a freer revving 5.3 engine than the longer stroke 6.0 from the XJRS/XJR-S???

I would say it is worth driving both, an 6.0 XJR-S engine has a different character to a 5.3.