hi,

the xk and xkr rear exhaust are very similar except of the bypass. Is the interior the same ? I assume they are identical, because of the cost savings during production and even the connection of the bypass is there. When I weld new pipes to the main exhaust body, I actually would get a xkr exhaust with a better sound for my XK, am I´m right ?! What you guys think ?

Cheers
Frank

 

As many XKR owners know, if they remove fuse 19 the active valves remain open. Why weld anything, just fit the XKR back box and you will achieve the same thing.

 

Thanks for the update, it´s an XK car so there is no fuse and there is no XKR back box. In this case I have to buy a XKR back box or I´m going to modify the mounted XK on.

 

The XKR Exhaust bypass will remain open if no vacuum... no need to do anything else if you want an "always open" XKR muffler.

The XK muffler has a passive system that opens up the bypass as pressure increases.

Has anyone done this to an XK that can comment on if it is worth putting an XKR muffler on and XK with no other mods?

 

Oh yeah! Not only gives the cat a nice pur under normal driving, you get a real braaap when you punch it, and the quad tips just look so much better than the dual tips (in my opinion).

And if you use the 'sport mode', those throttle blips on the downshift are much more pronounced.

 

Ive also done it .

The xk has one mid pipe resonator and dual exhaust .

The xkr has two mid pipe resonator and quad exhaust .

My suggestions would be to keep the xk set up and replace the mid pipe resonator with a crossover x-pipe (2.25") this will not only balance out the exhaust pulses, improve tq/hq and in your case increase the sound.

Now if you still not satisfied with the improved tone go ahead and purchase the xkr quad back box and bolt that up.

As there won't be any vacuum attached to the exhaust diaphragm(valve) on the xkr back box all 4 tail pipes will be set permanently in the open position

 

Having just upgraded from my previous X100 & loving the roar of the new car's exhaust, the X100 was way too quiet, could someone please give me an update on the principle of operation of the X150's active exhaust?

Thanks

 

It's computer controlled, using a combination of the engine RPM and throttle position, to either open or close the valve flaps by applying or removing power to a vacuum pump. The vacuum pump is a separate item in the rear of the car, present in the XKR, not the XK, so the XK doesn't have the ability to control the flaps if you replace the XK's passive back box with an active back box from an XKR. Fortunately the normal state of the active back box is to have those valves 'open' for a louder sound. It takes a vacuum source to close them.
There is a chart that shows the state of the valves in the XKR, based on RPM and throttle position, don't recall if it's the owner's or service manual.

 

Steve - I've also swapped the stock XK box for the XKR box, and much prefer the beefier sound that comes with it. I noticed in your signature that you've opted for the 100 high flow cats. What is your setup and is it now (gasp) "too loud"?

 

If You take a look at my photo you will notice that the outer tailpipes are virtually clean and the inner tailpipes are dirty

The reasons for this is the fact the outer pipes are the unmuffled tailpipes that are controlled by the diaphragm which I have permanently shut closed now (so not active) and all the gasses go through the muffled tail pipe section, this is done for the sole purpose of trying to quiet this car down.

Mind you my current set up is 100cel cats + x-pipe mid pipe (no resonator) + xkr rear box (only 2 exhaust pipes open)

 

I'll bet that was loud! Almost like running straight pipes from the exhaust headers to the exhaust tips, yeeouch, the neighbors would be coming with clubs and pitchforks.

 

Yes your right it pretty much is a straight through exhaust system!

I remember driving home thinking oh my God i have completely ruined the sound of my car thankfully the xkr rear valves could manually be closed phew !!

 

Has anyone ever tried modifying the XK back box by drilling out the
flap springs, or rigging them open?

 

Interesting and I'd like to hear it. I can't imagine it's louder then my XKR with the PAE system and stock cats. Can't see the 100 cel causing excessive noise. Even if I run in dynamic mode with the pipes open the noise isn't that big a deal unless you're in a tunnel with the go peddle down.

 

There is a huge difference in noise from the 100cell cats vs stock cats

The stock cats are extremely restrictive as they house a 400cell and 600cell

A good balance would be a set of 400s

 

I would second that. When my cats were removed after one failed on my '07 XKR the car was undriveable so I had to get a custom resonator made.

The petrol smell from the exhaust got too much eventually so I fitted some Magnaflow 59975 high flow cats (200 cell?) and went back to stock for everything else. It became too loud again to run with fuse 19 out so I put it back in.

In comparison my '10 XKR is extremely quiet even with fuse 19 out. I am planning to put a PAE on it for performance reasons but I had read that it doesn't actually increase the exhaust volume, just changes the note.

 

How did you find the sound of the 200cells

 

Pull Fuse 19 behind the rear seats. That accomplished exactly what you ask.... IF you have Active Exhaust.

 

I wouldn't use them without fuse 19 in and I also had the benefit of a custom tune from Cambo so the exhaust valves closed at around 1000rpm then stayed shut.

The valves also opened on the overrun so I got quite adept at backing off the throttle then pressing it again to maximise the sound if I wanted to be a hooligan around town.

I did post it on another thread but this is what is sounded like with fuse 19 out:


I only had the car for a couple of weeks in this configuration before I sold it but once the adaptations had adjusted it seemed to pull particularly well so I think it appreciated the extra back pressure.

 

Seems the 400cells with fuse 19 in is the go

The 100s and 200s are loud