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.

[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!

[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.

[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

[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.

[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