question for modifiers

[golf3 20lt 8v]

got a 8valver been serviced by vag every 10,000 runs like new really pleased with it so much so havent been interested in modding.  however the more i read the more it seems that its pretty much standard to upgade air filters and exhaust.  but ive also read that to get the most out of your mods you need a remap otherwise the old ecu doesnt recognise any changes made to the car.  for instance heard that if you take the cat off without remap ecu thinks its still there ending up with no gains.
 
what im asking is if you fit a new filter that lets in more air will the ecu :

(1) adjust to increased airflow
(2) not recognise any change to engine but run ok
(3) worst case senario,  not recognise increased air take causing the engine to run slightly off sync.  probably running slightly worse than before.

number 3, if the case, would probably account for lots of stories ive heard about air filters and induction kits loosing bhp rather than gaining (no remap done) what do you think?

[Cupra Turbo]

Well I have a K&N and a Magnex exhaust (with CAT) and I notice a performance gain ... esp at higher speeds.

[golfvr6]

The ecu will adjust the fuelling to suit the airflow, unless you dramatically increase the airflow ie. turbo, you won't actually need a chip.
Re-mapping is still a good idea as it will make the engine run at its best for performance. BUT it is not essential.

[Cupra Turbo]

does it matter if u run with a MAS or without a MAS?

[golfvr6]

All fuel injection engines will have some form on airflow sensor.

[Cupra Turbo]

does it make any difference to performance etc if its a

Airflow meter or mass air sensor?

[golfvr6]

No not really

[Cupra Turbo]

Well that cleared that up then...

For the record I have a Hitachi MAS!

[AZZY]

i want to get a K&N induction kit for my 8v gti, theres 2 types 1 with hitachi MAS 1 without, i havnt got a clue which is right for my car.

can you please help me out?

[LostBok]

Decent filters will increase throttle responsiveness and give you a few bhp... exhaust will help it out as much again (more air in, means more air will need to go out!)... apparently around 5bhp on each.

My Milltek Jet, PiperX induction and ECU remap managed an extra 27bhp and made it VERY responsive. You can get a Milltek upgrade that uses the round / "stealth" exhaust pipe, that will look very subtle and almost stock, but give you the same performance increase.

But that's around ?500 that you WON'T get back on resale! ?700+ if you get it ALL done professionally, ?300-400 if you try doing it all yourself and just pay for the parts.