Project XFR: Cat Breath (Exhaust & Filter)

Sorry Roadies… we know it’s been a while since the last update of Project XFR – but, fear not, things are moving along quite nicely now, writes Andy Robinson.

After many miles of enjoyable “Jaaaaaaag” wafting and supercharged blasting – along with some rather fancy data logging – we have highlighted some areas of hidden potential and hatched a plan of action. And now, the first stage of modifications have been fitted and tested with some rather nice results.

Our first mission was to address the Jag’s breathing – done with the very simple step of ditching the standard, restrictive paper air filters with some free-flowing, cotton gauze K&N panel filters. Five minutes to fit and a 1,000,000 mile guarantee, for good solid gains = no brainer. I’ve lost count of the number of road cars I’ve fitted K&N panel filters to – always reliable! (Me too, Ed).

Having addressed the air coming in, it would have been rude not to address the gases going out – with an exhaust upgrade at the same time, right?

After some (very) careful thought, Andy Clark (our tuning genius) of AC Speedtech set about dissecting the standard exhaust – to see where it was most restrictive. Then he designed a bespoke system to suit the car, as well as future-proof it for further mods (& MOTs) down the line.

The final result was to remove the secondary cats (which were contained in the same housing as the primary) and replace the pipes from the cats all the way to the standard rear silencers with 2.5” stainless steel pipework. The standard centre silencer (with Jaguar’s version of an X-Pipe) was removed and in its place a proper ‘from scratch’ built X-Pipe put in the correct place to aid scavenging and even the pulses out in the system. This all radically improves gas flow and reduces back pressure = more power and torque, and a far, far better V8 soundtrack. Clever stuff.  The rear silencers weren’t left alone either: The passive valves were found to have quite a strong spring in them as standard and until they were fully opened the exhaust gasses were left to make a further trip round an extra pipe with in the rear silencers = wasted energy. The answer? Simply remove them and plate up the hole left by the now removed valves. Simples!

After a few miles were put on the car to let the Jag’s ECU adjust to the changes in gas flow, I’ve noticed Project XFR has become more responsive and the keen revvy nature of the Jag’s V8 has become even more apparent. It’s also taken out some of the hesitancy from standard, not to mention added a much better, more sporty tone. It now sounds like all XFR’s should from the factory – they are far too quiet as standard!

What did all this mean in terms of power I hear you ask?

Well, Jaguar claim stock figures of 503bhp and 461lb-ft. But we feel they might have been a touch conservative, because Project XFR is now running at a very healthy 552bhp and a peak torque value of 530lb-ft (but this quickly gets reined in by the electronic torque limiter to 480lb-ft, more than likely to save the gearbox from too much applied torque). I’ve been swapping exhaust systems all my life and that’s gains of about 50bhp and 70lbft, which is massive. I’m very happy.

Now, with the winter months upon us, mods and mileage in the Jag will take a bit of a back seat. But plans are afoot for some rather interesting mods come the nicer weather and when I can actually get more/any traction! 😉

Still, when I do go out, I’m enjoying the new V8 soundtrack, extra grunt and plenty of tail-happy action on these soaked British roads. 😉


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