The quickest way to more power with one of these is fit an M112 instead of the M90 - or better ditch the supercharger and use a turbocharger to recover the power lost to drive the blower. Estimates a few years ago from one of the team that created the XJR was that a turbo would put it over 400bhp.
The only thing against that is the whine from up front is so much fun..
Agree to that. But can’t keep away from a interresting topic/discussion like this so I add some thoughts.
Has to say, in defence of the trusty old M90, that even if not giving the very top hp numbers it certainly give a very pleasant driving experience, instant throttle respons and very wide power curve. Huge fun difference to the n/a AJ6.
And there is, as always, modifications I think is worth to try. Overdrive pulleys gives a noticable improvement. Porting the sc and smothing or removing as much as possible of every restriction in the inlet ducts will help decrease temperature and keep power up.
About the importance of keeping heat away I’ve seen some ”rule of thumb” figures, saying that
every 0.1 bar increase in boost will make the temperature rise 10 deg (C), every 30 deg temp increase is 10% less power. Consequently it’s quite possible that increased boost not always nessecarely give more power, especially if it’s merely caused of the air expanded by heat, the number of molecules are still the same.
A too high IAT will probably also have the ECU to protect the engine by retarding the timing and/or add fuel with even more power loss.
Can’t say for sure that the statements are entirely true, not very familiar to the physics involved. Someone with more knowledge of the laws of Boyle, Charles, Ideal gas or whatever is most welcome to correct or explain the mysteries.
If ditching the M90 I agree the M112 seems to be a ok next step, budget considered. At the same speed as the M90 there should be 25% more air flow. Suppose the disadvantages are similar to the M90, still the Roots parasitic losses and heating issues. If shopping for a M112 I belive, not very far fetched, that the newer genV is as efficient as it gets. Came, for Jaguar, with the 4.2 V8.
What I can see it’s not exactly a direct swap, will take some efforts to adapt the longer house and snout to the AJ16sc, tight around the intake/intercooler.
If to continue the speculations on possible budget options would a different way to go, if starting from scratch, be to use the n/a AJ6 or AJ16 engine. Bolt a M112 to it with air to air intercooling, high flow injectors and change the camshaft timing, the AJ6 dizzy will work fine. Basic stand alone ECU. The high compression is a concern, could perhaps be overcome if using E85. Have no idea how realistic that is but, on the other hand, if blowing a piston, n/a engines are common, no big expense.
For the turbo option I suppose it’s the impressive hp dyno record setting alternative but don’t know much about this. When I had the n/a AJ6 I bought two old T04 SAAB turbos for it but that project never really got going, had the AJ16 sc instead, belive that was the better decision.
Still, the idea of a turbo blowing into the M90, mentioned earlier in the thread, is a very tempting one. Multiplied boost and different approach.
If money no object I would put it, would need loads of it, on the newer Eaton TVS or the twin screw type.
There is a pdf file for download at the US JaguarForums, worth reading: ”JAGUAR XJR-6 Jag mag article.pdf”. AJ16sc engine w. Eaton TVS R1900.
For the current status of my XJ6 I’m afraid there is not very much to report, the off-season to-do-list has been sadly ignored and revised. The remaining prioritys right now is to widen the rear wheels a bit and to make some changes to the supercharger and the inlet air ducts.
I have been driving the car sporadically in some of the real cold winter days lately without any starting or idling problems so I have skipped the idea to make the idle stepper motor functional. Won’t bother to have the full sequential injection or COP either, it’s postponed for time being.
Had a set of old wheels lying, the idea was to try to sort of combine two rims into one wider.
The width has been increased from 6” to 7”, most of it on the inner side, the centerline offset is almost the same as before. Will do some minor out of round adjustments and have it pass a dynamic balance test before I decide if to use it and make another one the same way.
Next after the wheels will be to have this 80 mm throttle body to replace the original 72 mm. Make a new sc adapter and do some rearrangments to the air ducts.
Will post when things have progressed a bit more.
/Cheers
