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That was a surprise to me also when I 1st got my car. After going through the OM I found how this worked ...
Yeah, same here. Before I added the XKR back box to my XK, which doesn't have the vacuum system to control the valves, I was investigating 12v stepper motors I might be able to use to control the flaps. When I discovered that they are either fully open, or fully closed (no middle ground), I put the investigation aside, and just bought a vacuum pump to control them via a 'mild2wild' setup (which I haven't installed yet). Having run for almost a year now with those flaps fully open, I can see that there are times I might like to "tame it down", but I'm not sure I want to be limited to the fully open/closed scenarios, so I may go back to checking out options to put a 'volume control' on them.
I guess what I was trying to describe is the exhaust is nice and loud on start then abruptly sounds like it was shut off, then briefly turned on very loud at full volume at higher RPMs, then again abruptly turned off when letting off the gas, the transition seems too harsh and un-natural. I understand that is what it is supposed to do but I guess I did not realize that it is effectively like going from 0 db to 100 db back to 0 db without any transition. Kind of like watching listening to music at full volume and pressing the mute button on the amplifier on and off.
Hope that makes sense.
I know what your now getting at
There is no build up to the brutality of the exhaust at high rpm it's either off or on that makes sense
On a positive note how good does the cold start up sound !!
Last edited by steve_k_xk; 09-29-2016 at 01:01 PM.
Drove around a bit today, including freeway time, with fuse 19 installed. The results are somewhat strange, acoustically. Valves are open when starting the car and then close when driving normally, then open again when driving hard past 4K RPM, then close again at cruising speed. So it sounds loud when they are open but when they close, the exhaust becomes significantly muted and muffled like a factory non-modified exhaust. Going to keep it that way for a little while, then take the fuse out again or I may make it switchable.
I quite possibly feel a bit like an idiot at the moment and I am also wondering why this has not come up on any of the other threads regarding fuse 19 nor why I did not think of this before. Correct me if I am wrong about Jaguar's engineering, but while researching the "science" behind exhaust design (I am now determined to make a full custom tuned setup) I came across the reason for valved exhaust. It has nothing to do with noise levels, it is all about maintaining power at specific RPMs via exhaust velocity.
There are 2 exhaust paths for a reason. At lower RPM there is less volume of exhaust and thus lower back pressure so exhaust velocity must be maintained by having a more restrictive path, only one path is open, the other is kept closed via the valve. At higher RPMs there is of course more exhaust and pressure so the valves open the second path to lower back pressure and maintain velocity. Theoretically with the valves open full time, full power will be achieved at higher RPMs but power would be lost at lower RPMs. I have to assume the engineers at Jaguar know what they are doing and it is probably best not to second guess them.
I quite possibly feel a bit like an idiot at the moment and I am also wondering why this has not come up on any of the other threads regarding fuse 19 nor why I did not think of this before. Correct me if I am wrong about Jaguar's engineering, but while researching the "science" behind exhaust design (I am now determined to make a full custom tuned setup) I came across the reason for valved exhaust. It has nothing to do with noise levels, it is all about maintaining power at specific RPMs via exhaust velocity.
There are 2 exhaust paths for a reason. At lower RPM there is less volume of exhaust and thus lower back pressure so exhaust velocity must be maintained by having a more restrictive path, only one path is open, the other is kept closed via the valve. At higher RPMs there is of course more exhaust and pressure so the valves open the second path to lower back pressure and maintain velocity. Theoretically with the valves open full time, full power will be achieved at higher RPMs but power would be lost at lower RPMs. I have to assume the engineers at Jaguar know what they are doing and it is probably best not to second guess them.
You are probably correct, but it sounds better all the time with them open all the time, at least I haven't tired of it yet.
Since my XK can't control the valves on the XKR exhaust I installed, they are open all the time. I had thought about using a 'mild2wild' switch to manually control them, but now I wonder if that might be a bad idea, as what will be the result of hitting WOT with the valves closed? Probably not a good thing.
I quite possibly feel a bit like an idiot at the moment and I am also wondering why this has not come up on any of the other threads regarding fuse 19 nor why I did not think of this before. Correct me if I am wrong about Jaguar's engineering, but while researching the "science" behind exhaust design (I am now determined to make a full custom tuned setup) I came across the reason for valved exhaust. It has nothing to do with noise levels, it is all about maintaining power at specific RPMs via exhaust velocity.
There are 2 exhaust paths for a reason. At lower RPM there is less volume of exhaust and thus lower back pressure so exhaust velocity must be maintained by having a more restrictive path, only one path is open, the other is kept closed via the valve. At higher RPMs there is of course more exhaust and pressure so the valves open the second path to lower back pressure and maintain velocity. Theoretically with the valves open full time, full power will be achieved at higher RPMs but power would be lost at lower RPMs. I have to assume the engineers at Jaguar know what they are doing and it is probably best not to second guess them.
Jahummer we have every right to question the engineers at Jaguar as they have the issue of trying to build an exhaust whilst keeping it within budget (so no mandrel bends) and also tolerable emissions.
With the exhaust valves open or closed on a system of that size my vehicle had no significant difference in power or torque at any rpm (measured on dyno)
Maybe if it was 3" we would have seen a different result and the valves would have come into play
The other thing we should be looking to develop is a large bore header system
If you look in the workshop manual for the 4.2L it only seems to mention noise as a reason for the valve on the XK:
"The rear muffler unit includes a Semi Active Muffler (SAM) valve. This valve is operated by the pressure in the exhaust system. At low engine speed the valve is partially closed to provide a more refined noise quality. At higher engine speed the increased pressure within the exhaust system opens the valve to provide a more sporting noise."
But on the XKR it does actually mention that it is to reduce back pressure as well:
"The rear muffler unit incorporates an active exhaust system. The active exhaust system is designed to give a more sporty sound and also reduces the back pressure in the exhaust system by opening a valve in the second exhaust outlet pipe."
If you lost power at lower revs with the valve open you wouldn't have thought that the 5.0L cars would open the valve permanently in the sportier gearbox modes.
Guys, I have the fixture ready to build the 5.0L Cats, I just simply need a factory set on hand to complete. I just have the XF-5.0 On hand to play with and the length is different from the coupes. If anyone is willing to send their factory set, I'll negotiate quite the savings for you.
Steve, don't you worry about the headers. I have a surprise for everyone's eyes before X-mas is it works out with work schedule. Yes, this means finally the set of amazing headers I've been planning.
Just a little eye candy. Just finished up the F-Type awd cars rad covers and engine kits. Ready to produce.
Hi. I am looking for downpipe catalytic 200 cell for my jaguar xkr
Originally Posted by FrickenJag
I wanted to separate some of the project topics I'm working on. This being one.
An upgraded high flow Cat design for the 06-09 Units. Wrapping up the design for the 5.0L shortly. Just need to get some stock units on hand to design from.
These will be a Tig welded 304SS 200 Cell High-flow design. EPA Compliant emission standards.
A cat delete option will be offered as well. I would recommend using a Cat simulator to prevent codes in that case.
I've been running this design in 16ga on an 08 XKR For testing. I've had one efficiency light in 6 months. This was due to not letting the car warm up prior to driving off.
For the final design I may up to 14ga wall to help contain more heat and heat the cat up faster.
More than likely the finish will be ceramic coated to aid in preventing heat transfer outside of the cat as well as a nice appearance. Ceramic chrome is what I'm leaning towards. Although I have been talking with a supplier that may be able to blend Racing green.
I'll be working on designs for the XKR and F-Types as well as mid-pipes next.
Regards,
Derek Fricke
Hi. I am looking for 200 cell downpipe catalytic for my jaguar.
Do you have a 4.2 or 5.0? post back after you install them. I am very interested to hear 200 and 300 cel cats on a XKR-S. I feel like mine is a tad quite.
Do you have a 4.2 or 5.0? post back after you install them. I am very interested to hear 200 and 300 cel cats on a XKR-S. I feel like mine is a tad quite.
Hey guys.
Pertaining to XKRS with 200 cell, I’ll toss up a sound clip and video this weekend. Sounds so nice. What I’m loving about it is no drone and just a clean powerful sound.
Pedro shoot me an email or pm.
Hey guys.
Pertaining to XKRS with 200 cell, I’ll toss up a sound clip and video this weekend. Sounds so nice. What I’m loving about it is no drone and just a clean powerful sound.
Pedro shoot me an email or pm.
Where did got it done, how much did it cost? Lima9016@gmail.com this is my email.
09-28-2016, 12:19 PM
