After reading the stainless headers discussion, I am considereing a question that was asked there (in some for or fashion). What are the best perfomance upgrades for the XJS? Selfishly, I am asking about the 4.0L slant 6 in my 1994.

What are the highest perfomance gains without regard to money?
What are the best bang for the buck upgrades?
What are the easiest upgrades?

Personally, I'm not racing but a little extra umph here and there would be appreaciated out of the old AJ6. Also a little curious about what the top end could be; just how much perfomance/HP can you get out of the AJ6?

 

I have absolutely no idea what's available from the aftermarket, but assuming I had reasonably deep pockets, I'd do this:

Visit a reputable tuner, and tell them I'd like the following:

- upgraded intake
- upgraded exhaust
- supercharger
- ECU tune
- suspension firmed up a touch
- brake upgrades if necessary

I don't know what the compression ratio is like for the 6 cylinder engine, but if it needs modified pistons, etc. to drop it before the supercharger application then I'd have that done, as well.

Still wouldn't expect to get too much out of it, but it would have to be a serious improvement over stock - which is what - 240HP?

 

This might be of interest.
Jaguar XJS Enthusiasts' Club (XEC)
trouble is - would you really want to tell your insurance company that you 'modified' your XJS ?

 

Cadfael, I totally understand why you ask. Simply put, 7.8 sec 0 to 60 is nothing to smile about, especially when compared to today's Jags, even the non-supercharged ones, right?
Well, I happen to own the same car as yours, but mine does 0 to 60 in 5.2 seconds. If that puts a smile on your face, you're reading the right post because I have some good answers for you. I could write a couple of pages here, but you'd be much better informed about this if you just visit my XJS presentation here:
http://www.cardomain.com/ride/210516...guar-xj-series
It's not brief, but it does explain clearly and in detail where the power comes from.
I have a lot of real nice mods and goodies on my XJS, but none of them has made me happier than achieving power that rivals that of my XJR; none.

 

Forcedair1, that looks like a labor of love! Gonna sit down at lunch and read your page thoroughly.

Also, I forgot to mention in my first post... upgrade the transmission (at least on the 12 cylinder models).

 

Thanks, Flint
It's #4 of all Jags at Cardomain. Have no idea why the crowd has voted my XJR as #1 instead, and over the XJS. The XJS merits far surpass my XJR effort and, yet, people have not seen it the way I see it. Jeez, I've done all the work, I should know...

 

I had a 1993 XJS convt with a factory 5 speed. The upgrades I did at the time made it a great highway cruiser but not the off the line acceleration. The parts I used came from Roger Bywater @ THE JAGUAR AJ6 ENGINE - 3.2, 3.6, AND 4.0 LITRE / AJ6 Engineering

The intake manifold they have gives a noticable increase, along with the adjustable air meter & the elimanition of the catalysts that go under the rear seat. These mods made the car a lot of fun to drive. We also turned the cams 2 teeth as well for more high end. You car looks fantastic. I wish you the best of luck with it.

 

I have discussed power issues and the AJ6 Eng'g mods with Roger several times in the past and I was very close to get the "High capacity airflow meter", the "Plus flow" and the "Plus torque" conversions and the "silencer substitute pipes" conversion, but not the "XJS TT extractor system" because it eliminates the front cats with downpipes and that's a no-no for the "visual" smog test here in California. Unfortunately, soon after that the Dollar took the steep dive and everything went double the price in no time, reaching way over 1,000.00 pounds, so I had to postpone the project.


All of Roger's mods improve mid-to-high rpm's performance, so, yes, they're great for highway enjoyment.

 

I meant that the over 1,000 pounds became, like, US$2,000.00 The nearly doubling of the price is hard to swallow when you could've....

 

I have a 1990 xj6 with the aj6 inline 6 4.0 and was curious about performance options the car came (from factory) with about 220 horses and around 378 lbs of torque. I want around 300-400 hp and about 500-700 lbs of torque without swapping to a chevy motor. options? feel free to add me as cody phelts on facebook if i forget to recheck here.

 

Cody,
I just noticed that your post is actually near two years after the last post on this thread, and 1 1/2 months old already. Have read this entire thread yet?

First, let me clariffy something...
You say that your XJ6 came from the factory with 220 HP and what you want is 300 to 400 HP, right? This means that we're looking at an increase of 80 HP (36%) to 180 HP (82%) and I'd tell you right now that you won't reach an 80 HP increase with just "soft" mods, such as air intake, exhaust, head porting/polishing, re-programmed chip, although all these together may add to some 55 - 65 HP increase along with a real good tuning, but know that all above mods are "rpm-dependand-mods", meaning that you need about 3,000 to 4,000 rpm's to feel the difference.

For anything that you'd feel the very moment that you hit the gas pedal you need to push EXTRA air in there and that's not necessarily rpm-dependand, i.e. a supercharger (S/C) or nitrous injection (N2O), with a turbo as a distant third, because of turbo lag. But a S/C for a 23 years old Jaguar will put you down at least some $20K to $25K (unless you do a good part of it yourself) because it'd be a totally one-of-a-kind-project on a very, very limited market car, let alone the nearly non-existing Jaguar owners who would want this. It most likely would have to be an Aussy, Brit, or even NZ enthusiast place because here in the US there's no enthusiasm for these things, unless you're a BMW, or Mustang, etc. owner. Lots of S/C alternatives if you own a Challenger, a Chevy, a Mustang and several others because of the tremendous popularity of these cars (i.e. ownership volumes) plus the ever enthusiasm of their owners.

This is why I opted for N20, which gives you at least the initial kick of S/C, if not more, really (I have both) and the cost is a fraction of a decent S/C installed, in the vicinity of $3K to $4K, that is for the UK system that I have and the support/protection goods that I have added. A US system may be substantially less, but I wouldn't know for sure. Did I mention to you that with 350 HP at max injection, my XJS has done 0 to 60 in 5.2 seconds? But I'm almost sure that, should I 0-to-60 race it against my XJR it would be ahead until like 50 mph with a very close finish.

Nitrous is not a "mystery", it's simply added oxygen so you can add more fuel along with it, nothing else! It comes in a bottle in the form of N2O (mixed with nitrogen) at 1000psi so it stays liquid until injection time. Very easy to install, absolutely.

There you have it.

Cheers

 

A chevy conversion....LS engines are easy to get to 400+HP Small block LT1's start out at 300HP and modest upgrades can get you to 375hp. Custom build LSX, 383 or an older 406 can net you 450HP for under 6000.00 with a transmission. If you Super charged or nos'd that AJ6 you'd see just 350HP.

If your AJ6 powered Jag is nice sell it to someone who appreciated it for what it is. If you've got the bug for a refined sleeper performance car the Jag platform is ideal and look for one with a blown motor and save it from the crusher. The strong rear suspension and large engine bay work out well for high powered chevys. The isolated front and rear subframes are pure genius and keep the refinement. Power is addictive...I know I have a 400HP Jagrolet that is currently under the knife. The chevy engine is out for higher compression pistons, bigger cam and many other supporting minor upgrades that should net 475HP and still idle smoothly.

 

The Chevy conversion is awesome. I can attest to that myself, as I used to have an older series II XJ sedan with a Chevy and a 700R4. The same combo with one of the newer and far more powerful engines would be a phenomenal car, but if I had to change the engine now I would rather stay 100% Jag, which still allows me to go for a supercharged Jag engine, the newest engine that was possible.

The low N/A power on the AJ6 engine (219 HP), makes it hard to reach the power figures that you can get with the 5.7 L V8's. Heck, even when I'm increasing power by 59% it can still reach only 350 HP, like you stated.

And this brings the S/C power increase issue. The S/C in my XJR adds 80 HP to the 290 HP of the N/A engine. This means that the S/C gain is a conservative 27.6% power increase. That is not very efficient and I'd assume that this is the kind of power that Cody would get from a supercharger, if that route was possible. The power increase with my nitrous system is 130 HP, or 59%, meaning over double the equivalent S/C gain in my XJR, yet, the 12psi boost is not necessarily conservative.

If I was to go with an American V8, it would have to be a S/C 6.1 L Hemi on the latest Challenger; best looking car other than my XJS/XJR....