I have a Hi-Flo Cat and exhaust system and have noticed big gains from it. People have always doubted the figures but I know it has knocked a couple of seconds off the 0-60. Now uses very low revs to get moving and sounds amazing. The only thing I can't get is a downpipe but I think Jetex do one. Although getting a bigger bore on the downpipe may affect the lambda on the 2.0 as it already has 2 pipes coming down, so has reasonable flow already.Yes, I got them.
Very nice piece of kit and a huge weight saving over the standard items. I don't think they give you any more flywheel power but they reduce the transmission loss so you end up with more at the wheels. I haven't had any problems with them and the ancillary belt hasn't noticably deteriorated (which some pros have claimed).
The only dificult one to fit is the alternator pulley. It's a lot easier to remove the alternator and swap it, than to try and move the ancillaries out of the way.
The engine revs and picks up a lot quicker since fitting them and there is a noticable step up in power at 4500rpm but this maybe a MAF or oxygen sensor problem with my particular car.
In all honesty, for the 2.0 8v, they are a bit of a bling item, although I think you can swap them over to a 1.8T should you change motors so don't bin your old pulleys. With the pound so strong at the moment I am tempted with the Neuspeed cam and lightened adjustable vernier pulley. Neuspeed claim a 10% increase in power but ?350 odd plus fitting kit and fitting it make quite a high ? per bhp figure. Although, at least with a remap and a RR session the timing can then be optimissed to run on the super unleaded's. If She passes the MOT without needing any work I may just treat her to one - or a 25bhp NOS kit.
The main problem with the engine is it's age. It was old before it went into the mk3 but at least in that it still had some reasonable poke. But to pass the Euro 2 emissions VAG had to really strangle the power that, coupled with the added weight of the mkiv, means it struggles - in comparrison with the Turbos.
Incidentally, there don't appear to be any off the shelf high flow Cats for the 2.0. Milltek e-mailed me recently to say they have no intention of producing one.
If you are prepared to break the law you could get a Cat from a breakers yard, smash out the Cat internals, weld in a piece of straight pipe inside the Cat housing and you'll have a de-cat pipe that looks like a standard pipe. It will mean changing it each time for the MOT, unless you can find a 'friendly' garage. I think this would make a huge difference to the engine - but there is that risk of breaking the law. Although, as it would look like a VAG item from the outside you could say the Cat must have broken - Yes I'll get a new one Officer and a test cert to show compliance.
Welding the OEM downpipe to the stainless steel one isn't a good idea. Blueflame used a flange on mine - Airtight but means when the original part rusts, I can replace it with a salvage part quite easily without cutting into the exhaust again. Plus you may experience leaks as the old part rusts against the stainless steel. The stainless exhaust expands at a different rate too when heating up so likely to break apart after a few months.Pulleys sure sound the way to go!!! If anyone knows a way to get them at US prices shipped to UK - that would be great! We can't be expecting the guys at Awesome, very good & helpful chaps that they are, to adjust their prices relating to $ to ? variations.
My car's just come back from my mechanic and the cat's definately had it. The nasty rattle, that I thought might be an exhaust hanger or something, turns out to the the core of the cat!  However, they did swap out a faulty coolant temp sensor and a leaky brake servo vacuum hose.
Probably why I have the same 4.5k big step up in power (like mk1fan) and the car runs rough and gassy smelling! Also, I have two different o2 sensor check codes - 1 lean (how??) and 1 intermittent no signal. Surprised the o2's aren't saying rich, rich, rich with effectively no cat.
The silver lining is this - I get to justify a new high-flow cat!  Should go a treat with my 3" piped Scorpion cat-back. Noisy though, but what a sweet noise!
I've been speaking to TSR and they will weld a high flow cat into an OEM downpipe for me, which should be just the job. However, the have confirmed that the Supersprint high-flow manifold/downpipe is a LHD part. D*mn LHD parts! TSR get my recommendation as v helpful chaps!!!
Thanks for the input all u guys!
Off topic - I have just had OMP brake hoses and DOT 4.1 fluid fitted... what can I saw but WOW!!! Best brakes on any car i've ever driven, I though my companies Caddy mk5 vans were good (and they have like 330mm discs all round)!
Hi,I poped up to AMD in oxford last week to enquire about getting mine remaped. They said with a ram air, a miltek cat back system, and a remap they can guarentee between 148-155 bhp. Thats quite a steady increase if you ask me. Well worth the money!