I'm crap at explaining things but I'll have a go. An internal wastegate is built into the turbo, whereas an external wastegate is seperate. Here you can see an exhaust manifold designed for an internally gated turbo: http://www.ukstarletclub.com/forums/upload...-1238818504.jpg now compare it to the externally gated version which has an extra pipe, this is where the external wastegate goes: http://www.ukstarletclub.com/forums/upload...-1238819263.jpg The gases are then either plumbed back into the exhaust system or just vented straight out to the atmosphere, hence "screamer pipe". For an internal wastegate you'd use a "seperated" decat which has two pipes, one for the exhaust gases from the turbine (which goes through the exhaust system) and one for the exhaust gas from the wastegate, which goes straight out rather than through the exhaust system. Alternatively (and much more common) you'd just use a normal decat where both the gases from the wastegate and turbine go into the same pipe. An internal wastegate is quite simple, it is operated by an actuator, when it reaches a set pressure the wastegate opens. External wastegates are generally regarded as being "better" although internal ones are quite capable of doing the job, however there can be problems such as boost creep. You're better off googling these things or having a search on the forum though as I said I'm not too good at explaining things.