Perking up XJS performance

Perking up XJS performance

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Discussion

sheepy

Original Poster:

3,164 posts

219 months

Tuesday 14th October 2003
quotequote all
OK, no-one's posted on here for a while, so lets see if I can trigger something.

I've currently got a 3.6l XJS (straight-six engine). She's pretty swift once you get the revs up over 3k, but a bit stodgy below that. So, what can I do to improve her? I'm not looking to replace her, so suggestions like "buy an XK8" etc aren't helpful . Rather I'm looking for suggestions for what I can do in terms of tuning or minor mods just to perk her up a bit.

Sheepy

V12Bob

646 posts

218 months

Tuesday 14th October 2003
quotequote all
Try speaking to AJ6 engineering,they may be able to suggest some mods, or you could fit a V12

If you look at Jaglovers, the yanks seem to fit chevy v8's, so how about trying a Tiv motor.

OR
You could look at my V12 in PH classifieds

>> Edited by V12Bob on Tuesday 14th October 12:10

bobfrance

1,323 posts

237 months

Tuesday 14th October 2003
quotequote all
Well I suppose the air filter is always a good place to start.
Going a little bit dearer; would it be possible to get the ECU tweaked? I know it can be done for my 12.

I think the early x300 series XJRs had the straight 6 with a supercharger on it. Could you possibly get one off a scrapper and fit it to yours? Or failing that, the whole engine.
I can ask my "expert" it that can be done.

Alternatively you could try removing weight from it (always fancied a carbon fibre bonnet).

Or tweaking the handling to make it faster around the corners. Low profile wheel/tyres, roll bars, springs/dampers. Perhaps even nicking those bits from a scrapped sports model?

Hope that's given you food for thought.

sheepy

Original Poster:

3,164 posts

219 months

Thursday 16th October 2003
quotequote all
Thanks for the replies.

Hmm, pinch the engine out of an XJR, that sounds like a good idea. I'll do a swap with FWD's during the next LB Meet n Beer, he'll never notice the difference

Seriously though, a supercharger was inline with what I was thinking. I never realised that the early XJR had the "same" straight-six, might be worth an investigation.

I'm working on the handling at the moment. Nothing drastic, just replacing things like springs and shocks. I've no idea of the age of bits on her, so replacing them seems like the best policy.

AJ6 have quite a few "nice" ideas. I think I'll exhaust the "routine" things first.

As to "upgrading" to the V12. No thanks, why would I want to cart all that extra weight around? I deliberately chose the 3.6 because the front end is lighter, the performance isn't too much lower, and I could still have a manual.

BTW, anyone changed the front springs on an XJS?

Sheepy

bobfrance

1,323 posts

237 months

Friday 17th October 2003
quotequote all
sheepy said:
Seriously though, a supercharger was inline with what I was thinking. I never realised that the early XJR had the "same" straight-six, might be worth an investigation.

I think it's the case. I can check with my expert for you though.
Alternatively one of the later AJ16 straight 6's will be more peppy anyway.

Bigger wheels with lower profile tyres may help the handling/feel but of course they won't do anything for the ride comfort.

You could speak to the guy on here who is fitting a TVR Speed 6 engine into a TR6. He sems to have plenty of Ideas.

Just think a SP6 engine in an XJS! At least you'd be more likely to come out of it alive than in a Triumph.

sheepy

Original Poster:

3,164 posts

219 months

Friday 17th October 2003
quotequote all
Hi Bob,

I'd appreciate feedback from your expert. These are really long term ideas that I'm mulling over. The simplest idea may well be to buy a tatty early XJR and simply swap the engines (along with any other bits needed). The XJR could then be sold on as simply a non-supercharged car, and the XJS would benefit from the improved engine.


Anyway, any feedback welcome,

Sheepy

FourWheelDrift

82,961 posts

254 months

Friday 17th October 2003
quotequote all
sheepy said:

Hmm, pinch the engine out of an XJR, that sounds like a good idea. I'll do a swap with FWD's during the next LB Meet n Beer, he'll never notice the difference



Mine's a Supercharged V8 anyway, so PAWS OFF!

PS. I bet I could improve it's 0-60 time, do you know this place called Beachy Head?

>> Edited by FourWheelDrift on Friday 17th October 16:49

sheepy

Original Poster:

3,164 posts

219 months

Wednesday 22nd October 2003
quotequote all
Changed the front springs last night. What a bloody awful job!

I used threaded rod on the wishbones to lower the spring-pan slowly (can't use a normal compressor). This sort of worked ok, would hate to try and get alignment any other way!

The job went thus:

Half an hour to get started, put the car on a lift etc

An hour to remove the first spring. Well, was expecting that, the first stage of any job always takes longest.

Twenty minutes to install the new spring (now that a technique using two people on the rods had been sussed)

Fifteen minutes to remove the other spring. Unfortunately the two bolts which go through the spring-pan and upto the shock-mount both snapped.

Fifteen minutes to drive the snapped bolts out and find replacements.

An hour and a half to install the new spring. Of that we spent a hour getting one sodding bolt in Turns out that the spring-pan on the off-side is deformed slightly. It's fine once in and bolted up, but it's a right fking ct to get the last bolt in. Took several of us using various bars and clamps to pull the pan into alignment and get the sodding bolt in! That was easily far worse than pulling the engine and gearbox out of the MGB!

Four hours! To think I believed my tutor who said it would take less than an hour a side! We were quite lucky that the college security didn't get too huffy and chuck us out (We're meant to be out by 9.30pm with the college all locked up and secure by 10pm. I left at about 10:30pm!)

Anyway, first impressions: The front of the car is much higher now. The first few seconds of accelerating or braking aren't spent rocking the car, so she's a bit more nippy. The headlights may need adjusting, but I'll give it a few days to let the new springs settle.

I'm going to fit new front shocks on Friday (I've got the day off), and so by Sunday's LBMnBIII I should have a pretty decent front-end!

Sheepy

Edited to change my awful spelling

>> Edited by sheepy on Wednesday 22 October 11:29

V12Bob

646 posts

218 months

Wednesday 22nd October 2003
quotequote all
IIRC JEC have specialy made spring compressers for the XJ-S. The advise not to try replacing suspension components without them.

Pleased to hear that you are happy with the front end, are you thinking of having a go at the rear as well?

Will you be using gas shocks, or the standard variety?

sheepy

Original Poster:

3,164 posts

219 months

Wednesday 22nd October 2003
quotequote all
I did the rear springs in the summer. Surprisingly enough, all four shocks at the rear were tested by one of my college tutors and found to be pretty much as new.

The rear ride-height was too low on one side, and replacing the springs sorted it out.

As for the "special" compressor, Jaguar supposedly sells the correct tool, but I was advised by a guy in the States to use lenghts of threaded rod. Basically, the wishbone has four captive nuts. Remove one bolt, replace it by a length of threaded rod with a nut. Repeat for two other bolts, and then remove the remaining three bolts. Now you can slowly wind down the three nuts on threaded rods. No problem!

The idea worked like a charm once we got a rythm going, the nearside spring took twenty minutes to install and the offside sping fifteen minutes to remove. It was only the awkwardness of installing one bolt that meant we took so long to finish. If we'd not snapped two nuts and had such a trouble reinstalling one bolt, then we'd have been finished by about 9.15pm!

Ah well, I'll hopfully never have to do that again!!

Sheepy