XJS exhaust system - it's 2019... any new sources?

I will attest to the quality of the Simply performance exhaust components. I bought cat less down pipes from them and welded in bungs for the O2 sensors. I initially installed the mid-box delete pipes but found the sound a little too loud for the convertible and the wife’s ears so I went back to the mid-box mufflers. I still have a nice sound without being overbearing.

Kirbert… I’ll buy your book! What’s the title, link etc.? My first Jag, as in one I personally owned vs. the one dad bought (1961 Mk II 3.8) new, was a 1966 Mk II 3.8 which I rebuilt the engine, repainted etc., only to, after having it all fixed up… being stolen! 2 brothers have since owned a range of jags but this is my first personal foray (my return!) and I bought it November of 2017 w/ 28,500 miles on it… indeed, I’ve hardly had time to drive it anywhere! Your book will be a welcome addition to the collection… bring it on! :slight_smile:

gcoder… wow, that looks great, thanks for sharing! With my model the cat’s posed a problem as they apparently didn’t have them in England. This meant they could not supply the forward sections as theirs would not work w/ my cats. They offered the entire system (like yours) but this early on, I figured I better not get too carried away as this entire project only got legs because the mid sections needed replacing.

http://www.jag-lovers.org/xj-s/book/Jaguar.html

Thanks! It is downloaded and now I’m really going to be in trouble :slight_smile: Say, tomorrow I’ll find out how much I like the new sound… or not. Will advise. Thanks again! ps. have you written anything about Alfa’s? :slight_smile:

Somebody would have to buy me an Alfa.

Hahaha… well, I bought a new one for my wife back in 1987 and years on it still rock n rolls w/ about 150k on the odo! Great fun and always easy on the eyes… and would you believe reliable? Never left us stranded albeit time to freshen up some suspension bits, hence the ask. Sign up for Bring a Trailer aka BaT and enjoy their daily listings, never mind the comments… they shake down every posting fairly thoroughly. Oh, and back to Jags, love the new sound! And so does the wife so we’re all good! Have a great weekend…

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I did that. The change in tone and loudness was rather subtle…and probably just right for most.

I wanted a bit more so I changed the rear mufflers as well.

Here’s the rub:

If you do much to increase the sound you end up with that rather peculiar Jag V12 tone. It’s an odd sound, really. You have, in a sense, two straight-six engines running simultaneously.

On my present V12 I have four straight-thru mufflers and, this time, on advice of others, included an “X-pipe”. Surprisingly pleasant sound, no drones, and closer to the “V12” sound that most people are expecting

Cheers
DD

Doug, that sounds like a great idea (the x pipe). I’ll have to check out my brothers because he’s done something to his system and, I think you’ve nailed it, sounds peculiar… as you say two sixes running in tandem. At this point I’ve simply eliminated the rear mufflers and I do like the sound.

If the two exhaust tracts remain separate, that’s actually what it is. Side dual exhausts would really accentuate the effect, as the sound on either side of the car would be that of a 6-cyl.

There’s been much debate on the issue of whether or not a crossover or an X-pipe does anything for performance on a V12, but I suspect most would find that it helps the sound.

It’s available here on this forum. I’ve found it invaluable. and I owe many many thanks to Kirbert.
It’s called Kirby Palms XJ-S As a matter of fact, I incorporated one of the IRS mods on my Jag Mods channel. The one thing I noticed is there isn’t across over pip to help scavenge exhaust pulses. The cross over will help quiet things down just a bit at an idle.

Looks nice! I’ve heard an uncorked V12 and I’m with Kirby; it’s not really a nice sound; unfortunately not like a Ferrari. but there’s a team of boffins that tune the exhaust to sound so magnificent.

Nicely done!

Hey, if you have a Digital P car, unscrew the oxygen sensors and fire 'er up!

If you ever have the exhaust system out for any reason, don’t miss the opportunity to start it up with only the downpipes in place and take it for a drive! Early Sunday morning probably wouldn’t win you any friends in the neighborhood, but it’ll be a memorable experience.

Kirbert, while I’ve got your attention but shifting away from exhaust (hope this doesn’t require a new thread), any thoughts on what’s contributing to poor fuel mileage? Again, mine’s a 1992 XJS V12 w/ 30k on it, 1,500 of which I’ve managed to add since I bought it 18 months ago so there’s still the learning curve but, 8 miles per gallon? Why, when we head off for Montreal late next week I’ll need a fuel truck following me. Wife won’t mind the mileage because for once she won’t have to beg me to pull over for a break :slight_smile: I skimmed the fuel section of your excellent book but may have missed it. Sounds good, pulls well but mileage stinks which, while I wasn’t expecting a free ride in a V12, just want to be sure there isn’t a problem my mechanics missing. Thanks!

If I were to do my exhaust over again i would consider using the chambered pipe’s as used on the 65 to 67 Corvette side pipes & HP Cameos. I think they would fit nicely with a little welding. They probably are very pricey but cheap compared to some of the systems out there,

Yeah, 8 MPG ain’t right, there’s something wrong with the car. Offhand, I’m wondering if the cold start circuit is remaining active when it’s supposed to cycle off. I’m not even too sure what all the cold start system includes on a '92, but presumably it keeps the vacuum advance locked out to fire up the cats. That’ll kill your mileage big time, although I dunno if it’d get you to 8 MPG.

Another possibility is that the infamous jumper has been pulled. The Marelli ignition system has a jumper located somewhere near the brake master cylinder. It’s supposed to be in place, only pulled in the event of getting a tank of bad gas. Without the jumper the car performs poorly and gets lousy MPG but it doesn’t knock.

Any possibility that a brake is dragging? Or your handbrake doesn’t fully release?

Thanks so much for the ideas/suggestions! I’ll run these by my jag mech (Jim) tomorrow when I drop it off. I’ve mentioned this to him once before, he said he made some adjustments but whatever those were, didn’t solve the problem. It’s not the brakes, had those done… no brake odors. Jim did say no one drives 12 cylinders and whines about the mileage… and I won’t as long as this is normal, normal I thought being more around 12 - 16 city/hwy. Don’t want to be spooked out of taking this rascal to Montreal but the Mercedes (CL 550) does have a nice ride!

Do you make a lot of short hops with the car?

I drove without the jumper quite a bit when I first got my car (89 Marelli). Premium was crazy expensive for my budget at the time and I was a little concerned that it would knock even with Premium. The butt-meter says there was perhaps a 10% decrease in “pep.” Nothing catastrophic. MPG dropped from 12-13 to 11-12. Certainly not to 8.

I am not so sure there IS a cold start circuit on a Marelli car. There is no vacuum advance to lock out.

I don’t have the details from the Book memorized, but could the car be in open loop with perhaps a buggy TPS…? The injectors think it is operating at higher RPM than it really is?

Peter, have you actually checked the mileage, old-school? Don’t believe whatever the trip computer is telling you unless you have verified the old-fashioned way.

Regards-
Bob

There’s no physical vacuum advance, but the Marelli 'puter simulates the same effect – and I’ll bet it simulates the cold start, too. So, how’s this for a theory? Perhaps the Marelli coolant temp sensor is bad and convincing the engine is cold all the time.

Back in the day I had a 79 Chevy Monza in which I installed a 350 small block. I had a GM HEI distributor, and not knowing better, I left the vacuum advance unhooked. Once I got educated, I hooked it up and highway mileage went from about 12mpg to 17mpg. Advance not coming in will definitely kill mileage.