The first thing you should do when modifying your engine is to make the airflow less restrictive, you can do this two ways. The first method is to buy an induction kit, doesn’t matter what make, they all do the same but they are roughly about £50+ for a decent one. Make sure it gets plenty of cold (dense) air by using a cold air feed.
The second method is to modify the standard air box. You can do this by drilling holes in the side above the actual filter and drilling holes out to a larger diameter, you could also add aluminium piping to replace the standard hose and routing it to behind the grill to get cool air.

The next step is usually the exhaust, the gain the full benefit on an induction kit, it is wise to get a performance or custom exhaust with a decat pipe (removes the restrictive catalytic converter) After all, what goes in must come out... Expect to pay around £250 for a full system
Induction kit with a performance exhaust should give you 5-15 extra BHP depending on your engine; it will also make your sound a lot meaner…


A note from Matey-Matey about the G40 engine:
To improve airflow on a G40 the single modification is to remove the restrictor flange within the lid of the standard air box. This flange was (allegedly) placed there by VW during development to starve airflow in the final part of the rev-range so the car hit the limiter less!! - as we all know this is the place where the G40 is at its neck-wrenching best, so get out your file / Stanley knife and trim away the flange from the shoulder-spur at the top of the air box until the whole pipe is the same diameter throughout.
Whilst you have the air box open, pull out the silencer trumpet that connects the air box to the fairing around the headlight for a more convincing roar, discard all of the fairing gubbins to ensure more air flows from around the headlight, and finally garnish with a good quality aftermarket panel filter (if you are prepared to slightly shorten the life of your re-built supercharger!).

cheers for that.

anyone got any pics of a modified ait intake system on a 6n 16 valve engine? would like to see exactly how this is done..

Just thought I'd belatedly throw my 2p in here.

Induction kit - don't expect much (if any) power gain. Never noticed any difference with mine, bar the extra noise. Individual choice and all that, but I wouldn't bother. Panel filter cheaper and does just as much good (ie, not much)

Exhaust - cat will make the difference - but remember you can only remove it and still pass the MOT if you're running a pre Sep 92 car (OK - that's from memory, someone might correct me on the exact cut off date)

Also remember - bigger the bore, slower the flow. A 3 inch system might flow more gases, but the rate will be slower and you might end up with a back pressure problem. You'll also lose bottom end torque at the expense of higher revs (not much use if you're running a limiter). NOTE - stainless stell is thinner than mild steel - the resulting noise isn't to everyone's taste.........

Inlet/exhaust manifold - get them flowed (esp the exhaust manifold) and you'll see more of a difference than a replacement system (as they're more restrictive in the first place) - but the loss of torque is even more evident, so unless you've got plenty spare, be careful.

Anyway - just some pointers.............

Stainless steel is as thick as you want it to be. Material choice doesnt decide thickness.

Thanks for the helpful info