Advice needed on XJS 3.6 engine project - want V12 killer!!
Discussion
Hi...I am wondering if its possible to get V12 power out of a 3.6 XJS engine...for sensible money...what are the best mods?....The AJ6 Engineering site reckons their high torque manifold/big bore throttle/filter/straight through pipes will give you 45 bhp over the standard 220 bhp...for just over a grand...that sounds reasonable....but does it work?....anyone tried it?....I am thinking about a big valve conversion...I would like to keep it naturally aspirated....but rapid!...any help/ideas appreciated///
Back in the day it usually took the 4 litre version and/or turbocharging or supercharging to make the 6 cylinder AJ6 etc engines quick enough.But wether that would work out financially worth all the trouble involved in the conversion compared to a 6 litre V12 and individual throttle bodies with a manual box would be open to question.Especially if the V12 is then taken up to 6.8 litre using a big bore liner kit which is what I intended to do next if only I wasn't already spending all the budget on petrol and eaten radius arm bushes,rear hub shafts and rear wheel bearings.
Edited by XJ Flyer on Sunday 7th July 23:56
Ecurie Ecosse said:
Or fitting an XJR6 motor?
yes...that would be nice....but...probably cost a lot more than I am looking to spend...this is what I am thinking:1 swap the head for a later AJ16 4.0 head ( higher compression ratio, lighter/bigger valves )
2 swap the throttle for a 4.0 unit
3 Go with the Aj6 Engineering high torque manifold/air box/ecu
4 Go for either the AJ6 Engineering TT exhaust or some other high quality/proven unit
5 Possibly go with a performance branched exhaust manifold
I think all of that could be done within £3000...and should make for a very pokey motor...I am going to look into the various bits and bobs and get some prices...
A 4 Litre engine would probably be a better starting point and there should be a cheap plentiful supply of those around from old virtually worthless XJ40's.Then start bolting all the mods to that instead of the 3.6 with the additional cost over staying with the 3.6 probably being negligible.But a lot of people seem to make the mistake of confusing spending money on modifying the AJ6 to bring it up to standard type levels of V12 outputs and then thinking that's a V12 killer.When in fact in reality all they've done is spent more at the end of the day to get to the starting point of modifying the V12.In which case it's effectively using a modified 6 to just match the standard 5.3 Litre 12 let alone the 6 Litre 12 and let alone a modified 6 Litre 12 which is the most effective return on money spent.When it comes to getting the most output for as little outlay a possible bigger engines alaways beat smaller ones.
While remembering that any driveline advantages in the case of the 6's v the 12's are just an illusion based on the idea that anyone who's serious about making a 12 go properly will not have long ago thrown the 3,or even 4 speed,auto and 2.88 diff,if it's got one,in the skip in favour of a 5 speed manual and lower diff ratio.
While remembering that any driveline advantages in the case of the 6's v the 12's are just an illusion based on the idea that anyone who's serious about making a 12 go properly will not have long ago thrown the 3,or even 4 speed,auto and 2.88 diff,if it's got one,in the skip in favour of a 5 speed manual and lower diff ratio.
XJ Flyer said:
While remembering that any driveline advantages in the case of the 6's v the 12's are just an illusion based on the idea that anyone who's serious about making a 12 go properly will not have long ago thrown the 3,or even 4 speed,auto and 2.88 diff,if it's got one,in the skip in favour of a 5 speed manual and lower diff ratio.
OK I've got an XKR, but a manual gearbox and limited slip dif has made a different car of itXJ Flyer said:
A 4 Litre engine would probably be a better starting point and there should be a cheap plentiful supply of those around from old virtually worthless XJ40's.Then start bolting all the mods to that instead of the 3.6 with the additional cost over staying with the 3.6 probably being negligible.But a lot of people seem to make the mistake of confusing spending money on modifying the AJ6 to bring it up to standard type levels of V12 outputs and then thinking that's a V12 killer.When in fact in reality all they've done is spent more at the end of the day to get to the starting point of modifying the V12.In which case it's effectively using a modified 6 to just match the standard 5.3 Litre 12 let alone the 6 Litre 12 and let alone a modified 6 Litre 12 which is the most effective return on money spent.When it comes to getting the most output for as little outlay a possible bigger engines alaways beat smaller ones.
While remembering that any driveline advantages in the case of the 6's v the 12's are just an illusion based on the idea that anyone who's serious about making a 12 go properly will not have long ago thrown the 3,or even 4 speed,auto and 2.88 diff,if it's got one,in the skip in favour of a 5 speed manual and lower diff ratio.
you make a very good point...I guess I liked the idea that the 6 cylinder cars are lighter and nimbler...that's my main attraction...plus slightly lower maintenance costs.. While remembering that any driveline advantages in the case of the 6's v the 12's are just an illusion based on the idea that anyone who's serious about making a 12 go properly will not have long ago thrown the 3,or even 4 speed,auto and 2.88 diff,if it's got one,in the skip in favour of a 5 speed manual and lower diff ratio.
TWINTURBODAVE said:
you make a very good point...I guess I liked the idea that the 6 cylinder cars are lighter and nimbler...that's my main attraction...plus slightly lower maintenance costs..
Also, I think its not so important that I have a car that is faster than the best of the V12'S...perhaps I was a bit optimistic with my 'V12 Killer' heading! 
....I think as long as I can produce a car which is considerably faster than it is now, with excellent handling, I will be happy....its going to be a road car...I think over 300 ib/ft torque should be quite entertaining ...Ok...I have been looking into a XJR6 transplant....the actual fitting is straight forward...it's the same 6 cylinder engine and the gearbox is the same type...the problem is getting the engine to run with the ecu..it seems that the ecu is specific to the engine when leaving the factory...and that its not easy to override it to accept a different engine?.....is that correct?...I would appreciate someone in the know just telling me what the precise issue is...not the solution....just the problem..
I currently own '92 facelift XJS 4.0 Litre (5 speed) manual but have previously owned a similar vintage 6.0 litre V12 XJR-S.
My thoughts are that the XJR-S was a lovely car and the V12 is a really lovely engine, but whilst it was a great cruiser, the auto box ruined the performance and the car ultimately felt nose heavy when turning into corners. By comparison my 4.0 litre manual feels so much more lighter and nimble. Id's say a 4.0 litre manual is a faster point to point car than the XJR-S but obviously won't have the same top end speed.
Mine only has had two owners and only 46k on the clock and may be looking for a new home soon*.
Bob.
My thoughts are that the XJR-S was a lovely car and the V12 is a really lovely engine, but whilst it was a great cruiser, the auto box ruined the performance and the car ultimately felt nose heavy when turning into corners. By comparison my 4.0 litre manual feels so much more lighter and nimble. Id's say a 4.0 litre manual is a faster point to point car than the XJR-S but obviously won't have the same top end speed.
Mine only has had two owners and only 46k on the clock and may be looking for a new home soon*.
Bob.
- I also have a full factory TWR body-kit and stainless streel straight through pipes that could be fitted...
bobfrance said:
I currently own '92 facelift XJS 4.0 Litre (5 speed) manual but have previously owned a similar vintage 6.0 litre V12 XJR-S.
My thoughts are that the XJR-S was a lovely car and the V12 is a really lovely engine, but whilst it was a great cruiser, the auto box ruined the performance and the car ultimately felt nose heavy when turning into corners. By comparison my 4.0 litre manual feels so much more lighter and nimble. Id's say a 4.0 litre manual is a faster point to point car than the XJR-S but obviously won't have the same top end speed.
Mine only has had two owners and only 46k on the clock and may be looking for a new home soon*.
Bob.
Hi Bob...sounds interesting...any photos? My thoughts are that the XJR-S was a lovely car and the V12 is a really lovely engine, but whilst it was a great cruiser, the auto box ruined the performance and the car ultimately felt nose heavy when turning into corners. By comparison my 4.0 litre manual feels so much more lighter and nimble. Id's say a 4.0 litre manual is a faster point to point car than the XJR-S but obviously won't have the same top end speed.
Mine only has had two owners and only 46k on the clock and may be looking for a new home soon*.
Bob.
- I also have a full factory TWR body-kit and stainless streel straight through pipes that could be fitted...
bobfrance said:
I currently own '92 facelift XJS 4.0 Litre (5 speed) manual but have previously owned a similar vintage 6.0 litre V12 XJR-S.
My thoughts are that the XJR-S was a lovely car and the V12 is a really lovely engine, but whilst it was a great cruiser, the auto box ruined the performance
I know Chris at Winspeed has put manual boxes into V12 XJS before, so if you want the best of both worlds that's possible too.My thoughts are that the XJR-S was a lovely car and the V12 is a really lovely engine, but whilst it was a great cruiser, the auto box ruined the performance
a8hex said:
I know Chris at Winspeed has put manual boxes into V12 XJS before, so if you want the best of both worlds that's possible too.
Hmm, A manual box in a V12 would be very interesting, although you'd still have the heavier nose weight to contend with so it still wouldn't feel nimble.Probably like many XJS users what I really wanted was a supercharged straight six setup like those fitted in the DB7. I mean it is essentially a Jaguar AJ16 they used in the DB7 i6 so how hard can it be? The answer unfortunately seems to be pretty hard. Turbos are apparently simpler, but still rare and a bit costly to fit. The AJ6 engineering tweaks look good but each one delivers just a small increase. the mose economical improvement seems to be NOS, which isn't something I'd seriously consider, however I have seen it done very well in an XJS.
The other option is to try and take weight out of the car. A carbon fibre bonnet would be pretty neat...
Edited by bobfrance on Wednesday 10th July 09:29
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