XJ-S 12 Jag owner wants to upgrade

(XMarine) #1

I have a 1987 XJ-s 12 orginal that I am looking to upgrade the performance. I found a old website that had a few good ideas but when I look up the companies it list they are all gone or no longer selling the parts for my car. I know I can increase the tired size to 18x8 but the wheel company doesnt sell tires in the US and it doesnt tell me what tires must go on it to fit my car. Last thing I want to do is get the tires and wheels only to find it hitting the wheel well. Also I know I have to redo the exhaust that is easy but all the engine modifications seem to be outdated. I am on a limit budget and this is and was my dream car. I know it can be a fast sports car and still keep the style and class it was designed with. I dont want a loud rock hard machine but I dont want a granny car either. I am near phoenix and I can not find any muscle car shops around. I can not even find cool led lights to fit the headlights. Am I doomed with a car I can not improve or is there a secret to upgrading this classy car to be a real performer? It only has 40k miles so I really dont want to tear about the engine but I want options so when the tranny goes or the breaks need replaced I can upgrade as I go. I already need tires so am thinking of tires and wheel combo.

(Doug Dwyer) #2

AJ6 Engineering has some good upgrades.

The tall 2.88 final drive ratio blunts performance…further handicapped by the lazily-calibrated TH400 transmission. Many have gone to shorter gears (I went to 3.31) together with a 4-speed automatic (usually a TH700) with good results. Others have gone to a 5-speed manual. However, if money is tight, the old TH400 can be tweaked to be more responsive.

Lower restriction air intake and exhaust give mild improvements. Somewhere on these pages there’s an old archive showing various DIY air intake mods. I’ll try to find it.

Before doing anything, though, make sure the engine is running properly and delivering full power, as-is. Many don’t…often due to (for example) inoperative vacuum and centrifugal advance mechanisms and general lack of care.


(Bernard Embden) #3

I covered rim and tire upgrade on my website years ago. Info should still be applicable.


(Greg) #4

It’s many years down the road for me once I just restore my 88 XJS, but I agree, I’d like to convert this luxury cruiser into something a bit more racy.

I’ve been reading LOTS of people’s responses. The cheap simple stuff is convert to cold air intake. It will help a tiny bit at full throttle, but for me it will be mainly a nice sound thing. Another cheap fix is having a muffler shop remove the front mufflers, and just keep the rear ones. Again, a bit more performance, but mainly a sound thing. One day, I’d rather pony up the money and buy a full stainless steel system. Oh, and remove air pump and A/C, it’s a tiny bit less for the engine to run (plus makes working on engine so much easier)

Suspension-wise, I will probably upgrade to Koni shocks. I have found on my other cars they give very good performance without being too harsh, like Bilsteins. The stock Sage (is that right?) are just too soft. I haven’t looked into sway bars or suspension bushings yet, but I’m sure there will be choices.

Unless you want to rebuild the engine, I get the feeling the engine as-is is pretty performance worthy. The final thing to unleash this beast, IMO, would be to ditch any AT and put in a manual transmission. And like others have said, change the rear differential gearing. Those two changes are expensive, but it would definitely change this car dramatically.

I like what I see with this company regarding Manual swap and Exhaust system. www.simplyperformance.com I may give them a call once I’m ready, better start saving my pennies.

One last thing, I will not be doing ANY performance mods until I make sure the cooling system is 100% perfect. I may even replace the radiator just because. Running this car hard will tax the cooling system.

(Doug Dwyer) #5

Air intakes