1. Jack the car up and support it on the jacking points under each sill. Remove the engine undertray by removing the 16 8mm bolts. On the 135, one of the bolts is at the inside rear edge of the wheel arch on each side. The others are quite obvious.
2. Undo the screws securing the strip of plastic under the front edge of the bumper (10 in total) , and remove it from the car.
3. You will now have exposed the underside of the stock intercooler. Using your needle nosed pliers, or a flat bladed screwdriver, lever the c-clip out that holds the intercooler hose into each side of the intercooler. The c-clip will click when it’s in the undone position, then pull the intercooler hoses out of the intercooler.
4. Rotate the two clips on the underside of the intercooler to the ‘unlocked’ position, and remove the plastic piece under the intercooler that they were securing.
5. Using a T25 screwdriver, undo the screw on each side of the intercooler. Be sure to support the intercooler as you remove the screws as these are all that’s holding it in place.
6. Remove the intercooler from the car with care. On the 335 it’s necessary to bend back the lower edge of the bumper to facilitate removal. Take care that the clips on the back of the intercooler release from the fan shroud.
7. Both standard intercooler pipes need to be removed from the car. BMW use a ‘use once’ clip with a locking joint that needs to be prised apart with a screwdriver, or cut off with a dremel or similar.
8. With the hoses removed, mount the Forge intercooler reusing the screws removed in step 5. The Forge intercooler is heavier than the stock core, so you may need the help of an assistant to hold the core in place. Again, this is harder on the 335 as the lower edge of the bumper will have to be held out of the way to facilitate fitting.