My car is a USA spec car with the catalytic converter. The car is considered a collector’s car and no longer needs a new license plate or emissions testing. I do not know what a real Jaguar V12 engine should sound like. I know what the car sounded like when my father purchased the car new it was very quiet. I have an awesome high performance car with the looks, handling, speed. During normal driving the car has quiet deep purring V12 engine until you start the car, down shift or step on the accelerator then it has a real deep subdued growl. It is my Aston Martin DB9. I want the Jaguar to be a Grand Touring GT car like it was but only better. I want a smooth ride, low road noise, comfortable, tight handling, quiet purring sound at idle then I want to hear what the Jaguar V12 engine really sounds like. I do not want a loud screeching rice burning car with a fake muffler sound. I want a subdued growl that gives you the nervous feeling you would have if you were in the jungle and hear a low growl and you know it is a Jaguar somewhere lurking waiting to jump out any time, but when? I am an electrician and very mechanical. I have not really worked much on cars and don’t know what changes will influence the car's performance and sound. I am thinking about installing a larger air intake, filter and throttle kit. What would the car sound like if there was no catalytic converter installed. Is it true that if the Jaguar is tuned correctly with the correct adjustments to the ECU that the C02 emissions could be as low as if the car had the catalytic converter installed? Without the catalytic converter there would be less back pressure and more HP? Would the car be too loud without the catalytic converter and only have one muffler at the back end of the car? I have heard videos with the Milltek Sport and the Quicksilver but not the Bell exhaust systems. I like the quiet idle sound and tone with the Milltek when driving at a good speed but I think it should be a little throatier. The Quicksilver sounds a lot like my Aston Martin but noisier. Any recommendations for a system with or without the catalytic converter.

 

It’s impossible to “hear” the sound you want. So what you get will be people opinions of what they think it should sound like.
First the catalytic converters don’t really hurt power very much. Nor do the add or subtract much volume.
Personally I think the mufflers overly muffle the sound. But in my humble opinion you need the rear resonators to keep the sound decent. Not annoying.
Now can those resonators be changed to improve the exhaust note? Probably. Like I said people have different ideas of what is a nice sound.
The original goal of the car was to not offend Royalty or nobility. So a great deal of effort was spent to make things quiet. To the loss of sporty character.
Because the V12 is over 5 liters, it won’t have the high pitched scream of a Ferrari 3.0 liter. ( a sound I happen to love )
The good news is “headers” do absolutely nothing as far as sound goes and actually hurt horsepower slightly. Real racing headers need 27 feet of tubing to add 4% More horsepower. ( that takes a metal artist to fit them in).
Go to Camp Chaos chronicles by Robert Knodt on U-Tube to see what’s involved.

In Summation if it were me, I’d remove the mufflers replace with straight tubing and the try various resonators to get the exact sound I wanted.
ps. There is an additional 10 hp if you remove the inlet tube on air cleaners. You might hear a little more intake sound.

 

Your information and ideas are a great help. What is the largest exhaust pipe that can be installed? I heard the largest size is 2-1/4". What are your thoughts on the cone shaped resonators? I know the sound changes a lot depending on where the resonators are placed in the system. There is not a lot of room to install a resonator, before or after the rear axle. Any thoughts?

 

Megaphones ( cone shaped exhaust tailpipes) really tend to bark. While I like the sound it’s really not in the character of the car.
I think that since the XJS. Is more sporty then the 4 door sedans. It’s proper to put out more than a muffled exhaust. ( caution, purist will object and some can be real jerks about it)
The existing resonators are after the rear acle6.
The tailpipes can go up to 2&1/2 inches but it takes a real muffler artist to fit everything in without problems.
The temptation is to dump the exhaust out the side. Don’t! All anybody ever actually hears is 6 cylinders.
You need to run the pipes all the way to the back to get a 12 cylinder sound.
Tailpipes make a big difference in the sound. If they are curved down it’s a more subtle sound. Straight tends to be a little brassy

 

The cats make a very noticeable difference in sound. I just went through this. Tried a set of euro catless downpipes, much louder.

Main issue is that catless stinks, I couldnt drive the car like that, smelled like a 2 stroke.

Mid muffler delete gives a nice tone, not loud at all(with the cats).

i pulled out the pre-cats in the downpipe and retained the main cats after the O2 sensor.

 

Factory downpipes with pre-cats removed, main cats in place. Open downpipes only.


i tried this with catless euro pipes and it was way louder.

 

Long story short you're never gonna get the Ferrari V12 howl.....if that's what you're looking for.

I've experimented with several different muffler configurations on both my V12s. The result in all cases was/is rather odd tone that, IMO, sounds Ok inside the cabin....a bit of a muted growl....but just sounds a little weird outside the car.

My best result has been 4 glasspacks with an X-pipe.




This pic obviously doesn't show the rear mounted glasspacks

Without the x-pipe you have two separate 6-cylinder exhausts which produce a sort of "blatt" tone.

Whatever you decide on I would recommend the X-pipe for sure. It gives the exhaust a more V12-ish tone....but still a bit odd, mind you!

Cheers
DD

 

Doug,
I really like the look of your exhaust system and I bet it will sound great. I am talking with a company from England called Simply Performance and they have suggested going with a stainless steel exhaust like the original Bell system removing bothe Cat systems, keep the co2 heat sensor, remove the center box go with a straight pipe over the axle add a sound resonating box and same style tail pipe as the original only 1/2" larger. The original system is all bolted together rather than welded. Are there any issues the the bolted connections and leaking of co2 into the car?

I am also looking at a set of larger throttle bodies from the original 63 mm to 72mm with a larger filter cover, filter and air intake cone. What do you guys think?

What are peoples thoughts with removing the air pump and tubing system?

 

Your car revs pretty fast. Makes me wonder what Im missing.

 

aluminum flywheel.

 

My 76 XJ5.3C, has 2 1/2" system but still has centre mufflers and rear resonators. Engine has cold air intakes and after market sport air cleaners. From the drivers seat, the car sounds great but is a pleasant sound of induction. The exhaust is very quiet - at least at lower revs.

I have a spare V12 Coupe engine so thinking about exchanging the standard throttle bodies from it for larger and putting them on my engine. Also thinking of taking out the centre mufflers and replacing with a X pipe. Also looking at getting larger diameter exhaust pipe tips made to match the size of the exhaust.

I am interested how the mods suggested in earlier posts have worked out.

Garry

 

What luck! My flywheel is cracked and about to fly apart just like my idler arm did. I talked to a guy in England does racing spec ultra lite flywheels. Id very much appreciate your input as its simply a matter of time before she falls apart at...130kph.

 

mine is made by Holley, sourced via Drivenman. Fidanza makes a good one too.

 

larger exhaust pipes provide a slightly lower tone, ( think Tuba instead of trombone)
Dual intakes is not really going to gain you anything ( except complexity ). The stock throttle body provides all the air that the stock intake manifold and ports can handle. Porting both can gain you more airflow which if you add more fuel will give you more power. However the real limit is the stock camshaft. That was designed for maximum torque from Idle to about 3500 rpm. ( where most cars are driven).
Racing camshafts. Trade bottom end torque for higher power at higher RPM.
If you want power at normal RPM there is no replacement for displacement. Your 6.0 liter adds about 50 horsepower for 700 more CC’s
The engine will easily go out more at relatively low cost.
There is one other way to gain serious power without much complexity.
Turbo’s. No, properly set up they don’t blow up your engine. In fact all the million mile+ semi trucks use turbo’s.
Here are some basic facts of turbo’s.
Small turbo’s (T 2 size ) spool up fast and quickly provide boost at the sort of rpm normally used. About 25-30% more power than stock. If driven normally ( not in boost mode ) they don’t cost you any more fuel. But once the boost gauge goes positive you’re using more fuel.
If you have a stone stock engine with about 20,000 miles or more on it and limit your boost to about 6psi, you don’t need to do anything to it except adjust for proper fuel /air ratio. ( aftermarket ECU ). Stone stock with 50,000+ miles on it you can safely use 12 psi. That gets you in the 35-40% more power range.
Above that you are taking a slight chance. I have seen 30 psi on stone stock engines that are used in drag racing last for a very long time if when street driven they limit the boost to the 12psi area.
You do not need high dollar turbo’s. EBay or AMAZON turbo’s in the $130 ea range are lasting a surprisingly long time. You will also need a boost control the mechanical ones ($30-40 each )are fine, just double check that all the set screws are tight. the Higher dollar electronic ones should be checked as well but those you can simply dial in the boost.
6psi you can live with premium gas with E10 or E15.
12psi.? With a intercooler, Yes that too will work with the above gas. Or you can start using E85
And won’t need that intercooler.
There is a cheap fuel line sensor that will automatically adjust the tune for whatever fuel you’ve mixed together. So if you use premium instead of E85. You don’t make as much power. But the engine won’t be damaged.
Finally the turbo’s fit nicely under the front fenders behind and above the front wheels.
My race car is set up for T3/4’s and they are virtually invisable T2’s are even easier to fit.
One last comment, if you use turbo’s you don’t typically need mufflers the turbo quiets the exhaust.