OK, best advice before anything is fitted, is check the car for the common faults;
- Coil Pack recall: Phone or pop into your local VW dealer and ask them to check the database to see if your car is due any recall work. There was one issued for coil packs, but not all cars were affected (mine wasn't).
- PCV: The Pressure Control Valve is a known weak spot and the part has been revised by VW. Simple enough test, with the engine warm and at idle, remove the oil filler cap FOR A SPLIT SECOND ONLY. If the engine tries to stall, it's all good. If it carries on idling with the cap off, you'll need to replace this part (simple enough job). Link to part -
http://www.awesomegti.com/car/vw/golfmk5/ecs-oem-breather-update-kit-mk5-gti-pas-b6-jetta-2-0t- High Pressure Fuel Pump Cam Follower: Awesome GTI now offer the full replacement kit and is one of the most essential things to replace before anything else, even without a remap on the table. Link -
http://www.awesomegti.com/car/vw/golfmk5/2-0tfsi-cam-follower-replacement-kitOnce all the above is sorted out, you'll be at a good level to start tuning. Remember, any faults now will become exaggerated once you apply tuning, but most garages that do remaps will health check your car anyway.
So as for parts to apply, if you want to see the other side of 250 BHP and 280 Ft / Lb Torque, then consider the following;
- Panel filter in the air box
- Go Faster Bits DV+ valve upgrade
- Miltek cat-back stainless steel exhaust system
- Stage one remap
As options for each part go;
Air filter: There's 2 main types, oiled and dry. K&N are an example of oiled filter, and these offer superior filtering but run the risk of the oil on the filter coating the Mass Air Flow sensor (MAF) and causing issues (I run one of these filter, so far 've been fine). The other option is a dry filter, like Pipercross. These are a more fit and forget modification, just occasionally wash it out every 10K miles.
Diverter Valve: For the sake of fit-and-forget style, the GFB DV+ is the best option, as it utilises the OEM solenoid and works a chart (again, I run one myself). Forge do a valve too, but it's a bit more involved than the DV+ option.
Exhaust: Miltek is a tried and tested brand, but others will be able to help you with choices here.
Remap: R-Tech are the number one really, but I had mine remapped by AMD in Essex. Some people have had issues with the AMD mapping but I've not had any problems at all.
If you need any more advice or thoughts, first check out my project thread in the Mk5 section or send me a message and I'll see what I can do. I'm only going off of my own experience here so I'm sure others will guide you too.
