SPACK 68 Posted May 2, 2020 I have been driving my XF EFI without a CAT for about 20-22 years, 2 1/2 INCH STAINLESS STEEL, GENIE EXTRACTORS, AND a rear muffler., GREAT sound, how ever i have always found that if I accelerate through the gears, every time i change a gear, the car feels like it is being held back, it does not want to keep going, I have decided this week, WEDNESDAY, to put a HI-FLOW 100 CELL CAT ON. CHALK and CHEESE, The car wants to go, it feels like there is another 5-10 kws OF power there...any one know why this would be.I thought the straight through pipe would be better with no restrictions.. Share this post Link to post Share on other sites
deankxf 20,287 Posted May 2, 2020 2 hours ago, SPACK said: I have been driving my XF EFI without a CAT for about 20-22 years, 2 1/2 INCH STAINLESS STEEL, GENIE EXTRACTORS, AND a rear muffler., GREAT sound, how ever i have always found that if I accelerate through the gears, every time i change a gear, the car feels like it is being held back, it does not want to keep going, I have decided this week, WEDNESDAY, to put a HI-FLOW 100 CELL CAT ON. CHALK and CHEESE, The car wants to go, it feels like there is another 5-10 kws OF power there...any one know why this would be.I thought the straight through pipe would be better with no restrictions.. was there a hollowed out cat there or a straight pipe? i was told My the exhaust joint a hollowed out cat would not perform as well as a functioning cat... when i fitted a 2.5" exhaust on My XF over the 2.25" exhaust it was gutless, this was later TUNED back and for better top end power also(who knows if it would have made any difference if tuned properly with the 2.25" exhaust anyway) someone like @ando76 would be able to explain i would think, (and a modified, straight pipe through the cat = $10,000 EPA fine for the owner and the business who did it) 1 SPACK reacted to this Share this post Link to post Share on other sites
SPACK 68 Posted May 2, 2020 I heard such good things about these CATS, i decided it was time to put one on and obviously, it should have one on, mine was a straight through pipe from the extractors to the muffler at the rear.....I WENT OUT side and measured the diameter and it is 2 1/4 inch...any way the car works a lot better now.... Share this post Link to post Share on other sites
deankxf 20,287 Posted May 3, 2020 4 hours ago, SPACK said: ..I WENT OUT side and measured the diameter and it is 2 1/4 inch...any way the car works a lot better now this was My experience also, the bigger exhaust dropped power until it was tuned for it. .(mine was not EFI) i doubt it's got much or anything to do with the cat being in there there's been some great vidoes explaining exhaust sizing on engine masters etc. but most dynos don't begin measuring power till 3000rpm odd, where standard ish old crossflows really notice any power picked up or lost at 1500 odd. Share this post Link to post Share on other sites
ando76 4,354 Posted May 3, 2020 It’s probably more of a case that the cat brought the horrendous efi set up back closer to original parameters and hit an air fuel ratio that the engine liked. 2 SPACK and deankxf reacted to this Share this post Link to post Share on other sites
gerg 10,871 Posted May 3, 2020 My old man's pre-cat XF EFI took extractors and 2.5" system without issue. I don't think he even bothered tuning it. You could drastically alter the mixture with the bypass screw in the vane meter. Maybe yours was already running close to lean and got pushed too lean without that subtle back pressure that the cat gives. It really isn't that much in reality, it might be worth 5 HP in extreme cases. Sent from my CPH1903 using Tapatalk 1 SPACK reacted to this Share this post Link to post Share on other sites
SPACK 68 Posted May 3, 2020 Thanks guys, just wondered, it just FEELS and drives better.. Share this post Link to post Share on other sites
ando76 4,354 Posted May 3, 2020 3 hours ago, gerg said: My old man's pre-cat XF EFI took extractors and 2.5" system without issue. I don't think he even bothered tuning it. You could drastically alter the mixture with the bypass screw in the vane meter. Maybe yours was already running close to lean and got pushed too lean without that subtle back pressure that the cat gives. It really isn't that much in reality, it might be worth 5 HP in extreme cases. Sent from my CPH1903 using Tapatalk Yep, when they were new. Now I doubt any of those old systems would be close to being able to deal with anything. The pure wear and tear on the vane and all the other systems would just push them to next to useless. Hell if you even let the rocker cover seal and dipstick seal go they go into spaz mode. 3 gerg, dex and deankxf reacted to this Share this post Link to post Share on other sites
Mr Polson 10,214 Posted May 3, 2020 When I first registered my wagon it had the stock manifold and engine pipe/cat, with only one muffler.Soon gave it a set of headers afterwards, and then a few years later had to put a new cat in to have it re-registered, also put in a full OE wagon exhaust - 3 mufflers, can't say any of it seemed to make any difference to performance 3 deankxf, SPACK and ando76 reacted to this Share this post Link to post Share on other sites
SPACK 68 Posted May 3, 2020 I am not sure what has happened, it was just the changing through the gears, the car felt like it was being held back, but now that LAG has disappeared..the car seems freer, the lag, being held back, has gone.. Share this post Link to post Share on other sites