1) Free flow intake air box (BMC and K&N make good ones),
2) larger diameter exhaust pipes from the CAT (catalytic converter) back (there are many good ones Autotech, Leistritz, Remus, Sebring, ANSA are but a few… key thing is that they are TuV approved), (Be aware the CARB Rules apply in California regarding such modifications)
3.) Schrick makes a 268 degree inlet cam shaft that is easy to replace on the 4 cylinders DOHC engines that will instantly make a huge difference in performance… get a good torque wrench and new valve cover gasket and your good to go.
4.) Most gasoline powered VW power plants use an ECU that has two curves on it… one is for regular gasoline and the other for premium or High Test… switching out your ECU chip with a performance one will give you more juice at a low cost, but will require you burn only premium fuel, there are several good ones out there with Superchips from the UK as good as any,
5.) A quaife differential is an expensive enhancement that should be considered carefully… it is noticeable when accelerating from zero as compared to a stock car, but really has a high price tag for just a few tenths off the 1/4 mile times.
6). suspension upgrades are a good place to improve drivability; larger front and rear sway bars and uprated structs and shocks are always good… be careful about lowering Springs with it best to buy systems of Springs and struts/shocks that are designed to complement one another in purpose designed kits Such as Koni/Eibach or Bilstein/HR. If you like a very stiff drive quality for extra stiffness consider a front strut tie-bar that connects between strut towers under the hood; otherwise, it may be too stiff to your liking.
7.) Tires and brakes are about equally important to stop with assurance. An expensive brake upgrade while putting less than performance rubber down is a waste of your money. (Galfer makes a great Big Brake upgrade kit for VWs; as good as Brembo but 1/3 the price, but is generally unavailable in the USA, so you’ll need to find a suppler in the UK to ship it to you. A call to Autotech or Europarts might get you there faster.) Use upgraded pads or you may burn through them faster than you are accustomed.
8. Short shift kits take getting used to… if you are very good at operating a M/T then consider a short shift kit; otherwise, you will burn through your clutch much faster getting used to one… Sachs makes good clutch kits for VWs; Luk is a bit better! Short-shift kits are easy to install and good ones are sold by reputable suppliers.
Please remember to always buckle up for safety and this includes times when your on a race course and properly qualified, obey all traffic rules and track rules too! Drinking and driving never mix and driving a modified car which can accelerate much quicker makes it potentially more dangerous!